Japanese Earthquake and Tsunami: Implementing the Lessons for the UK Nuclear Industry

Transcription

1 Title of document Japanese Earthquake and Tsunami: Implementing the Lessons for the UK Nuclear Industry Summary of the Magnox Ltd. Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami Project Assessment Report ONR-DFW-PAR Revision 0 August 2014 Template Ref: ONR-DOC-TEMP-005 Revision 8 Page 1 of 53

2 Office for Nuclear Regulation, 2014 If you wish to reuse this information visit for details. Published 08/14 For published documents, the electronic copy on the ONR website remains the most current publicly available version and copying or printing renders this document uncontrolled. Office for Nuclear Regulation Page 2 of 53

3 EXECUTIVE SUMMARY Summary of the Magnox Ltd. Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami On 11 March 2011, Japan suffered its worst recorded earthquake. The epicentre was 110 miles east north east of the Fukushima Dai_ichi (Fukushima_1) site. There were six Boiling Water Reactors (BWR) on this site. Reactor Units 1, 2 and 3 were operating at power before the event and on detection of the earthquake, shut down safely. Reactor Units 4, 5 and 6 were shut down for maintenance, furthermore, Reactor Unit 4 was defueled, but with short cooled fuel in the reactor building spent fuel pool. Off-site power was lost and, initially, emergency diesel generator (EDG) power was used to provide essential post-trip cooling. Less than an hour after shutdown a massive tsunami from the earthquake inundated the site and destroyed the capability for on-site generation of alternating current (AC) electrical power with the exception of one emergency diesel generator serving Reactor 6. Significant amounts of electrical switchgear were lost, as well as loss of control and instrumentation equipment. Subsequently, alternative back-up cooling was lost and, with the loss of cooling systems, Reactor Units 1 to 3 overheated and the temperature of the spent fuel pools increased. The overheated zirconium cladding in the reactors underwent chemical reaction with water and steam, generating hydrogen, which resulted in several explosions causing damage to building structures. Major releases of radioactivity occurred, initially to the atmosphere but later by leakage to sea. The operator struggled to restore full control. The sequence of events that unfolded was in line with current severe accident understanding for prolonged loss of cooling at Light Water Reactors (LWR). The events at Fukushima were rated at 7 on the International Nuclear and Radiological Event Scale (INES); a major accident. In response to this major nuclear incident both ONR and Magnox Ltd. recognised the need to learn lessons from the events at Fukushima. Magnox Ltd. produced a summary report (Ref. 1) that described the work that had been undertaken to address the Chief Nuclear Inspector s Recommendations and Stress Test Findings (Refs. 2, 3 and 4). The Recommendations and Stress Test Findings captured the initial learning from the events at Fukushima. Magnox Ltd. also produced a series of their own considerations that are also addressed as part of their summary report. This report presents the findings of the ONR review of the summary report. Magnox Ltd. operates ten licensed nuclear sites in the UK (Figure 15), only one of these sites, at Wylfa in Anglesey, is an operating nuclear power plant (NPP). The other sites are in various stages of decommissioning. Oldbury in South Gloucestershire shutdown in early 2012 and is defuelling prior to decommissioning. Sizewell A has recently completed defuelling. The remaining sites have been shut down for at least five years. The defuelled sites are: Chapelcross in Dumfries and Galloway; Dungeness A in Kent; Berkeley in Gloucestershire; Bradwell in Essex; Hinkley Point A in Somerset; Hunterston A in North Ayrshire; and Trawsfynydd in Gwnyedd. The initial response taken by Magnox Ltd. following the events at Fukushima was to initiate a series of plant walk-downs and a review of safety critical systems, processes and procedures at each of their sites. The aim of these was to confirm that systems essential to fuel cooling and reactor integrity in an emergency situation, including seismic and flooding scenarios, continue to meet their design requirements and that those design requirements remain valid. Additionally an assessment was made to establish that a degree of resilience was in place to withstand an event beyond the design basis. These reviews were undertaken by suitably qualified and experienced personnel with appropriate central specialist support. Following these initial reviews, Magnox Ltd. provided a response to the Chief Nuclear Inspector s Interim Recommendations in July 2011 (Ref. 5). ONR then produced the Final Chief Inspector s report (Ref. 2) and a further Implementation Report in October 2012 (Ref. 6). The implementation report gave an update on the progress of work and set timescales for Office for Nuclear Regulation Page 3 of 53

4 closing the Chief Nuclear Inspector s Recommendations and Stress Test Findings. ONR concluded that Magnox Ltd. s response provided an appropriate commitment to fully address the scope of the Recommendations on a reasonable timescale. Magnox Ltd. also participated in the European Stress Tests (Ref. 7) developed by the European Nuclear Safety Regulators Group (ENSREG) and submitted a report detailing the analysis work performed at each of its sites. This work was reviewed by ONR (Refs. 3 & 4) and a number of Stress Test Findings (STF) were raised to further confirm the resilience and safety of Magnox Ltd. s sites against severe events. In responding to the stress tests Magnox Ltd. identified a number of Considerations to be taken forward that could make reasonably practical enhancements to safety. Magnox Ltd. has now formally responded to the ONR STFs and its own Considerations. To support the assessment of the licensee s responses in the three years since the events at Fukushima, ONR inspectors have routinely engaged with the licensee to understand Magnox Ltd. s approach to implementing the learning from the Fukushima accident. These engagements have taken a number of forms, including: site inspections, technical meetings and workshops, and inspection of plant walk downs. Magnox Ltd. has acknowledged that all of the Chief Nuclear Inspector s Recommendations are relevant but notes that not all are applicable to all of their sites because of different circumstances (e.g. having been defuelled or being no longer dependent on active fuel cooling). Magnox Ltd. accepts that all of the STFs focused on nuclear power generating facilities, apart from a finding specific to Sizewell B, apply to them. ONR encouraged Magnox Ltd. to implement reasonably practicable safety improvements to support the remaining life of the stations, with a focus on the higher hazard sites. In order to ensure that prudent measures were implemented at Magnox Ltd. s sites, workshops were held where less focus was placed on long term study work, which would not have been completed or implemented within the remaining operational life. Consequently a number of prudent improvements were implemented at a relatively early stage at Magnox Ltd. s sites; these tended to be straightforward measures which provided genuine safety benefit. Examples of early safety improvements implemented included: Increased CO 2 and diesel fuel stocks on-sites, well above those required by operating rules existing at the time; A new diverse pond water emergency filling line at Oldbury and Sizewell A (see Figure 1 & 2); Provision of backup feedwater/fire pumps on-sites to provide further defence in-depth (see Figures 3 & 4); Development and implementation of improved training in respect of the Symptom Based Emergency Response Guidelines (SBERGs) and Severe Accident Management Guidelines (SAGs); Additional stocks of essential equipment (e.g. basic tools, flash lights etc.) on-sites stored in diverse locations (see Figures 5-8); and The purchase of a water tanker for transport of water from a nearby fresh water source to site (Wylfa) (see Figure 9). Magnox Ltd. furnished site work lists to ONR, which provided an overview of planned or implemented work being undertaken at Magnox Ltd. s sites. The work programmes provided by Magnox Ltd. in the progress reports were at a strategic level; however they did provide an overview of the key milestones for implementation of safety improvements. In general the intent was to complete most of the work within 2013, although some work continued into The key milestones have been met and Magnox Ltd. submitted Ref. 1 in December 2013 with a small number of residual activities carried over into The work carried over will be Office for Nuclear Regulation Page 4 of 53

5 complete by the middle of 2014 at which point Magnox Ltd. will issue a revision to Ref. 1 to close out any stated commitments. ONR s review of Magnox Ltd. s submissions has been commensurate with the importance of remote large scale severe events, as highlighted during the events at Fukushima, and the degree of vulnerability which might exist particularly beyond the design basis. However, it is recognised that a proportionate interpretation of work scope and duration is needed in relation to the Magnox Ltd. fleet, due to the limited operational life and subsequent defueling activities planned for the Magnox Ltd. sites. These aspects have been considered throughout ONR s review of Magnox Ltd. s submissions. In addition to the early safety improvements various work streams resulted in further key improvements to implement the learning from the Fukushima events and address ONR s Recommendations and Findings. Magnox Ltd. improved the extent of resilience enhancements to Control & Instrumentation (C&I) systems and equipment associated with plant condition monitoring, and secondary control capabilities in emergency facilities. It was apparent from the information supplied by Magnox Ltd. that the modification to the C&I systems formed the basis of a proportionate way forward for work that satisfied ONR s expectations and this was followed by satisfactory implementation. Magnox Ltd. considers the Recommendations and Findings associated with external hazards are now closed on the basis that site enhancements and plant modifications against seismic, flood and fire hazards have been completed. ONR agrees with this position. For the longer term review items, cross-industry groups have been established and Magnox Ltd. has played an active role in these groups. The cross industry groups will report back in due course. Magnox Ltd. undertook immediate improvements to increase the resilience of their fuel storage ponds to extreme events. This included additional lines for pond refilling (Figures 1 and 2) following a severe event. Magnox Ltd. has also confirmed that they already have suitable equipment for leak repair and associated processes in place, therefore ONR judges the licensee s work on fuel storage pond resilience to be reasonable and in accord with its expectations. Magnox Ltd. recognised that the ability of staff to respond to a major incident in a calm and measured way was integral to the successful implementation of an emergency response. Human factors and emergency planning staff, within Magnox Ltd., reviewed guidance in beyond design basis accident management procedures as well as the adequacy of training and exercise arrangements and implemented improvements to enhance human performance during extreme conditions. Magnox Ltd. procured a range of containerised back-up equipment to support sites in the management of a beyond design basis accident, or an event (Figures 5, 7 and 8). The containerised back-up equipment includes mobile diesel generators (Figure 10) and isolation transformers that can be used to supply existing systems and equipment at sites. The ability of a site to communicate with emergency responders, technical experts, local authorities etc. is vital to the successful response to a severe event. Magnox Ltd. s response, in the context of communications, is considered to broadly satisfy ONR s expectations as it has correctly focussed on those issues that should offset the vulnerability of existing conventional telecommunications systems against disruption to their infrastructure by plans for the introduction of mobile satellite telephones (Figure 11) and wireless communications (Figure 12) at sites, which will provide diversity in this area. Magnox Ltd. reviewed the transient accident analysis that supports the severe accident management advice. A key element of one of ONR s findings was that the review of the Symptom Based Emergency Response Guidelines (SBERGs) and Severe Accident Guidelines (SAGs) should take into account improvements to the understanding of severe accident progression and phenomena. ONR considers that this is recognised by Magnox Office for Nuclear Regulation Page 5 of 53

6 Ltd. s response in reviewing and revising the SBERGs/SAGs, part of which incorporated findings from a limited scope Level 2 Probabilistic Safety Analysis (L2 PSA) study for Wylfa. The L2 PSA provides an input for severe accident management measures and associated operator actions. This enables analysts to understand the risk profiles of different plant and identify any vulnerability that might be reduced by implementing improvements. Apart from Wylfa the remaining sites are permanently shutdown and are undergoing either decommissioning or defuelling. Magnox Ltd. did not consider ONR s Recommendation (FR4) to be relevant to these sites and ONR agrees that the development of L2 PSA for these sites would provide little or no safety benefit. ONR considers that Magnox Ltd. has made reasonably practicable safety improvements in response to the Recommendations, Findings and Considerations identified from the lessons of the Fukushima accident. ONR supports Magnox Ltd s position in closing the Recommendations and Findings. However, some Recommendations and Findings relate to longer term activities and where appropriate ONR will continue to monitor these via normal regulatory business. ONR s Recommendations and Stress Test Findings are complemented by Magnox Ltd s own Considerations. The Considerations support and inform the scope of the Stress Test Findings and Magnox Ltd has carried out work to close the Considerations on the same timescales as ONR s Recommendations and Stress Test Findings. ONR also supports their closure. Office for Nuclear Regulation Page 6 of 53

7 LIST OF ABBREVIATIONS ALARP BDBE BSL BSO CESC CNS Corium Design Basis DBE DNO DEPZ EC EDF NGL ENSREG EOP FRAMG HIRE HOW2 HSE IAEA INES NDA NGET ONR PCER PCSR PSA PSR REIC RGP Safety Margins As low as reasonably practicable Beyond Design Basis Equipment Basic Safety level (in SAPs) Basic Safety Objective (in SAPs) Central Emergency Control Centre Civil Nuclear Security (ONR) The high-temperature mixture of fission products and liquefied components, once they have melted due to the decay heat and a loss of cooling; from a nuclear reactor core, the mixture contains oxides, notably UO 2, fuel structure metallic parts and diverse dissolved materials. It exhibits similar behaviour to lava. The range of conditions and events that should be explicitly taken into account in the design of the facility, according to established criteria, such that the facility can withstand them without exceeding authorised limits by the planned operation of safety system. Design Basis Earthquake Distribution Network Operator Detailed Emergency Planning Zone European Commission Electricite De France Nuclear Generation Limited European Nuclear Safety REgulators Group Emergency Operating Procedure Fuel Route Accident Management Guidlines Hazard Identification Risk Evaluation (Office for Nuclear Regulation) Business Management System The Health and Safety Executive The International Atomic Energy Agency The International Nuclear and Radiological Event Scale Nuclear Decommissioning Authority National Grid Electrical Transmission Office for Nuclear Regulation (an agency of HSE) Pre-construction Environment Report Pre-construction Safety Report Probabilistic Safety Assessment Preliminary Safety Report Remote Emergency Indication Centre Relevant Good Practice Safety margins identify the gap between a considered situation and the threshold situation beyond which the probability of accident is not Office for Nuclear Regulation Page 7 of 53

8 SAG SAP SBERG Severe Accident SFAIRP tolerable. Severe Accident Guidelines Safety Assessment Principle(s) (HSE) Symptom Based Emergency Response Guidelines A fault sequence which leads either to consequences exceeding highest radiological doses given in the basic safety level on-site: 500mSv, off-site: 100mSv for initiating fault frequencies less than 10-4 per annum or to a substantial unintended relocation of radioactive material within the facility which places a demand on the integrity of the remaining physical barriers. So far as is reasonably practicable Single Failure Criterion This criterion sets that, during any normally permissible state of plant availability, no single random failure, assumed to occur anywhere within the systems provided to secure a safety function, should prevent the performance of that safety function. SHWP SQEP SSC SSHAC TAG Walk down Seismic Hazard Working Party Suitably Qualified Experienced Personnel System, Structure and Component Senior Seismic Hazard Analysis Committee (ONR) Technical Assessment Guide An on-site systematic review of a structure, system or components (SSC) by a small team of suitable, qualified and experienced persons to review the SSC capability to withstand defined hazards. Office for Nuclear Regulation Page 8 of 53

9 TABLE OF CONTENTS 1 INTRODUCTION PURPOSE OF REPORT assessment and inspection work carried out by ONR Matters arising from ONR s work Background Chief Inspector s Recommendations Recommendation IR CONCLUSIONS Recommendations REFERENCES Tables Table 1: Report Recommendations Figures Figure 1: Emergency Pond Water Filling Line at Oldbury Figure 2: Emergency Spent Fuel Pond Filling Line at Sizewell A Figure 3: Diesel Driven Fire Pumps at Wylfa Figure 4: Diverse Flood Resilient Boiler Feed Pump at Oldbury Figure 5: Beyond Design Basis Emergency Equipment Containers at Oldbury Figure 6: Enhanced Stocks of Staff Welfare Supplies at Oldbury Figure 7: Beyond Design Basis Emergency Equipment Containers at Sizewell A Figure 8: Beyond Design Basis Emergency Equipment Containers Supplied to All Sites Figure 9: Road Tanker for Emergency Water Transportation at Wylfa Figure 10: Emergency Diesel Generators at Wylfa Figure 11: Satellite Telephones Supplied to All Sites Figure 12: Alternative Emergency Reactor Monitoring System at Wylfa Figure 13: Beyond Design Basis Emergency Equipment Compound at Wylfa Figure 14: Submersible Pumps at Wylfa Figure 15: Locations of Magnox Limited Sites Office for Nuclear Regulation Page 9 of 53

10 1 INTRODUCTION PURPOSE OF REPORT 1 On 11 March 2011, Japan suffered its worst recorded earthquake, known as the Tohuku event. The epicentre was 110 miles east north east of the Fukushima Dai_ichi (Fukushima 1) site. There were six Boiling Water Reactors (BWR) on this site. Reactor Units 1, 2 and 3 were operating at power before the event and on detection of the earthquake, shut down safely. Reactor Units 4, 5 and 6 were shut down for maintenance, and further, Reactor Unit 4 was defuelled but with short cooled fuel in the reactor building spent fuel pool. Off-site power was lost and, initially, emergency diesel generator (EDG) power was used to provide essential post-trip cooling. Less than an hour after shutdown a massive tsunami from the earthquake inundated the site and destroyed the capability for on-site generation of alternating current (AC) electrical power with the exception of one emergency diesel generator serving Reactor 6. Significant amounts of electrical switchgear were lost, as well as loss of control and instrumentation equipment. Subsequently, alternative back-up cooling was lost and, with the loss of cooling systems, Reactor Units 1 to 3 overheated and the temperature of the spent fuel pools increased. The overheated zirconium cladding in the reactors underwent chemical reaction with water and steam, generating hydrogen, which resulted in several explosions causing damage to building structures. Major releases of radioactivity occurred, initially to the atmosphere but later by leakage to sea. The operator struggled to restore full control. The sequence of events that unfolded was in line with current severe accident understanding for prolonged loss of cooling at Light Water Reactors (LWR). The events at Fukushima were rated at 7 on INES; a major accident. 2 In response to this major nuclear incident both ONR and Magnox Ltd. recognised the need to learn lessons from the events at Fukushima. Magnox Ltd. produced a summary report (Ref. 1) that described the work that had been undertaken to address the Chief Nuclear Inspector s Recommendations and Stress Test Findings (Refs. 2, 3 and 4). The Recommendations and Stress Test Findings captured the initial learning from the events at Fukushima. Magnox Ltd. also produced a series of their own considerations that are also addressed as part of their summary report. 3 This report presents the Office for Nuclear Regulation s (ONR) judgements on the progress made by Magnox Ltd. in response to the Recommendations in the Chief Inspector s report on the implications of the Fukushima accident for the UK nuclear Industry (Ref. 2), the relevant Stress Test Findings (STF) and licensee s Considerations (Ref. 3 and 4). The Considerations support and informed the scope of the Stress Test Findings and Magnox Ltd has carried out work to close the Considerations on the same timescales as ONR s Recommendations and Stress Test Findings. 4 This report considers the Recommendations and Stress Test Findings that are directed at the nuclear industry and those specifically targeted at Magnox Ltd., namely IR-8 to IR-25, FR-1 to FR-4, FR-11, STF-2 to STF-17, STF-47 and STF Magnox Ltd. operates and is the license holder for ten nuclear power plants (NPP) in the UK. Only one reactor at one site is currently in an operational state, this is at Wylfa in Anglesey, all other sites are at various stages of decommissioning. Oldbury in South Gloucestershire has only recently shutdown in early 2012 whereas all other sites have been shut down for at least five years and are currently either defueling or defueled. The defueling sites operated by Magnox Ltd. are at Chapelcross in Dumfries and Galloway, and Sizewell A in Suffolk. The defuelled sites are Dungeness A in Kent, Berkeley in Gloucestershire, Bradwell in Essex, Hinkley Point A in Somerset, Hunterston A in North Ayrshire and Trawsfynydd in Gwnyedd. 6 In its role as nuclear site licence holder, Magnox Ltd. has responded to the Recommendations of the Chief Inspector s report on the implications of the Office for Nuclear Regulation Page 10 of 53

11 Fukushima accident for the UK nuclear Industry (Ref. 2), and the relevant STF and licensee s Considerations (Ref. 2 and 3). The assessment of Magnox Ltd. s Summary Report (Ref. 1) has been undertaken by ONR assessors and reported in a number of reports based on the technical area of the submission (Refs. 8 to 15). This Project Assessment Report (PAR) summarises the assessments made within each of the technical areas in order to consider Magnox Ltd. s submission and approach to addressing the lessons learnt from the Fukushima accident on a holistic basis. 7 The reviews undertaken in support of this PAR (Ref. 8 to 15) are not standard permissioning assessments. Instead their purpose is to make judgements on Magnox Ltd s response to the Chief Inspector s Recommendations and Stress Test Findings and in turn a judgement on the resilience in place to deal with beyond design basis events. 2 ASSESSMENT AND INSPECTION WORK CARRIED OUT BY ONR 8 ONR has carried out a systematic review of the licensee s summary report (Ref. 1) and appropriate supporting reference documents to this report. Structured assessment guidance was used for the general expectations and specific technical guidance provided for each of the Chief Inspector s Recommendations (Ref. 2) that were targeted at the UK nuclear industry. ONR s reviews have been performed across the range of technical disciplines reflected in the Recommendations and Findings and are reported in Assessment Reports (AR) (Ref. 8 to 15). 9 Further to the assessment of the licensee s responses, ONR inspectors have also had a number of engagements with the licensee since March 2011 to understand Magnox Ltd. s approach to address the learning from the Fukushima accident. These engagements have taken a number of forms, including: site inspections, technical meetings and workshops, and inspecting licensee plant walk downs. In addition to these engagements ONR inspectors have also held regular telephone conferences with Magnox Ltd. These lines of communication have enabled ONR inspectors to stay informed on the licensee s progress in addressing the ONR Recommendations and Stress Test Findings and to influence where appropriate. 10 The assessment of Magnox Ltd. s responses has been undertaken by a technical team within the ONR consisting of a number of specialist inspectors. The summary Recommendations from each assessment report have been combined and are presented in Table 1 of this report. The same team has also assessed the submissions against the ONR Recommendations and Findings provided by EDF Energy Nuclear Generation Ltd. (EDF NGL). This was done to ensure that a consistent and proportionate approach has been employed across the nuclear power generation industry. 3 MATTERS ARISING FROM ONR S WORK 3.1 BAC KGROUND. 11 Magnox Ltd. operates ten licensed nuclear sites in the UK (Figure 15), only one of these sites, at Wylfa in Anglesey, is an operating nuclear power plant (NPP). The other sites are in various stages of decommissioning. Oldbury in South Gloucestershire shutdown in early 2012 is defuelling prior to decommissioning. Sizewell A has recently completed defuelling. The remaining sites have been shut down for at least five years. The defuelled sites are: Chapelcross in Dumfries and Office for Nuclear Regulation Page 11 of 53

12 Galloway; Dungeness A in Kent; Berkeley in Gloucestershire; Bradwell in Essex; Hinkley Point A in Somerset; Hunterston A in North Ayrshire; and Trawsfynydd in Gwnyedd At the time of the assessments described here Sizewell A was still defuelling, this has recently been completed. 12 Following these initial reviews, Magnox Ltd. provided, as requested by ONR, an initial response to each of the Interim Report Recommendations in July 2011 (Ref. 5). A review of the response was carried out by ONR inspectors to identify whether the response was adequate in terms of its scope and that appropriate timescales had been identified for progressing the Recommendations. ONR s views on the progress made by Magnox Ltd. at that time were provided in the Chief Inspector s Final Report (Ref. 2) which concluded that Magnox Ltd. s response to the Interim Report Recommendations provided an appropriate commitment to fully address the scope of the Recommendations on a reasonable timescale. ONR produced a further Implementation Report in October 2012 (Ref. 6) to update the progress made against the Chief Inspector s Recommendations. 13 Further to their initial response, Magnox Ltd. also participated in the European Commission s (EC) targeted reassessment of safety margins known as Stress Tests (Ref. 7) developed by the European Nuclear Safety Regulators Group (ENSREG). Magnox Ltd. submitted a report detailing the analysis work performed at each of its sites. This work was reviewed by ONR (Refs. 3 and 4) and a number of Stress Test Findings were raised to further confirm the resilience and safety of Magnox Ltd. s sites against severe external events. Progress on Magnox Ltd s addressing of the STFs is also reported in the Implementation Report (Ref. 6). During the targeted reanalysis work performed by Magnox Ltd. a number of Considerations were raised by the Licensee where they had identified that reasonably practical enhancements could be made. Magnox Ltd. has now formally responded to the ONR Recommendations, STFs and its own Considerations. ONR has reviewed these submissions within this report to confirm that Magnox Ltd. has responded appropriately. 3.2 CHIEF INSPECTOR S RECOMMENDATIONS 14 Magnox Ltd. has supplied submissions against each of the Chief Inspector s Recommendations in Ref. 1, these submissions have been supported by various interactions with Magnox Ltd. throughout the period post the events at Fukushima. Each Recommendation has been considered within ONR s Assessment Reports (Ref. 8 to 15), these assessments have been summarised below. ONR s assessment has concentrated on Magnox Ltd s submissions against the Recommendations that are directly applicable to the nuclear industry, these are: IR-8 to IR-25, FR-1 to FR-4 and FR-11. A summary of Magnox Ltd s response to each recommendation and ONR s assessment of that submission is provided below Recommendation IR-8 15 This recommendation states: The UK nuclear industry should review the dep endency of nuclear safety on off-site infrastructure in extreme conditions, and consider whether enhance ments are necessary to sites self sufficiency given the reliability of the grid under such extreme circumstances. 16 Magnox Ltd. accepted this Recommendation and acknowledged that it was relevant to them. The purpose of this recommendation is to ensure that sites will be self sufficient in the equipment and consumables necessary to maintain an adequate emergency response capability. Office for Nuclear Regulation Page 12 of 53

13 17 Wylfa has established a new beyond design basis emergency equipment compound at a location close to the site which permits easy access (Figure 13). This compound contains the necessary general equipment, tools, pumps and generators to be able to implement an emergency response plan to restore critical safety functions to the reactor. There are sufficient emergency welfare packs to provide food, water and first aid to staff remaining of site for a period of 72 hours (Figure 6). Radiological protection and other health physics equipment and consumables have also been provided to support response actions and the compound itself has command and control facilities and communications equipment (Figure 11) to enable overall management of the response activities. 18 Resilience of the compound has been considered and adequate flood protection is provided. The main storage facility is of steel framed construction with a rubber lined cover (RUBB ). This has the advantage of providing protection but also being lightweight so that that any collapse would be unlikely to extensively damage the equipment inside. The auxiliary stores within the compound comprise of ISO containers (Figure 5). 19 Wylfa also has taken action to confirm that there is a diverse range of seismically qualified tanks containing diesel fuel and water for reactor cooling. Some gas turbine fuel oil tanks have also been re-commissioned to increase resilience and a road tanker (Figure 9) has been procured to enable the tertiary feed tanks, which supply reactor cooling water, to be topped up. These are reasonably practicable enhancements and increase the potential that sufficient quantities of consumables would survive a beyond design basis event to provide adequate fuel and cooling for 72 hours. 20 Other sites have taken a proportionate approach to equipment procurement to enhance self sufficiency. This ranges from increased stock holdings, health physics monitoring and pumps for defueling sites to beyond design basis emergency equipment containers (ISO containers) for decommissioning sites (Figures 7 and 8). These containers provide equipment specifically to facilitate recovery from an extreme event where circumstances might involve isolation of the site from external supplies for a limited period. 21 Magnox Ltd s response to IR-8 is adequate and its closure is accepted by ONR Recommendation IR-9 22 This recommendation states: Once further relevant information becomes a vailable, the nuclear in dustry shou ld review what lessons can be learnt fro m the com parison of the events at th e Fukushima-1 (Fukushima Dai-ichi) and Fukushima-2 (Fukushima Dai-ni) sites. 23 Magnox Ltd. accepted this Recommendation and acknowledged that it was relevant to them. Magnox Ltd. forms part of a group of technical specialists in collaboration with other licensees to discuss this topic, and evidence is provided within the response that the differences between Fukushima-Dai-ichi and Fukushima-Dai-ni have been considered as well as relevant reports such as the IAEA mission report (Ref. 17). Learning from Ref. 17 has provided input to various Recommendations and Findings. Work has been undertaken with respect to electrical supplies resilience and this is discussed further Recommendations IR-17, IR-18 and Stress Test Finding STF It is considered that Magnox Ltd. s approach is broadly in accord with ONR s expectations; however the progression of this activity is largely dependent on the rate of information emerging from other international organisations. Given that such information will continue to emerge over the coming years any learning points for Magnox Ltd. will be taken forward as part of their normal business activities. Office for Nuclear Regulation Page 13 of 53

14 Magnox Ltd. therefore considers that this item is closed. ONR supports the rationale to monitor the issue as part of normal business and the decision to consider this item as closed Recommendation IR This recommendation states: The UK nuclear indu stry should initiate a revie w of floodin g studies, including from tsunamis, in light of t he Japanese experience, to confir m the design basis a nd margins for flooding at UK nuclear sites, and whether there is a ne ed to im prove further site-specific floo d risk asse ssments as part of th e periodic safety revie w programme, and for any new reactors. This should include sea-level protection. 26 Magnox Ltd. accepted the finding and acknowledged that it was relevant to them. Magnox Ltd. considers the item closed on the basis that a review of flood levels has been completed and conclusions reached about how and at which sites flood protection needs improving. Existing flooding assessments for the one remaining operational reactor at Wylfa were judged to be well-founded and in line with modern standards. The detail surrounding this assessment is also covered in the response to STF Two instances were found where, on the basis of the available evidence, the current safety cases may have underestimated the risk of flood water accumulation on site. These were at Trawsfynydd and Oldbury. Reassessments were undertaken at both sites (Refs. 19 and 20) to evaluate the likelihood of site flooding along with detailed consideration of potential consequences of flooding. This was supported by site walk-downs. Revised safety cases were then issued for both sites (Refs. 21 and 22), which demonstrated that the radiological consequences of site flooding are already adequately low and will continue to diminish as the sites progress towards the planned care and maintenance condition. Nevertheless site improvements at both Oldbury and Trawsfynydd have been undertaken, which include procurement of an additional back-up boiler feed pump for both reactors at Oldbury. The pumps are located above the maximum credible flood level. Provision of electrical isolation and re-power systems above maximum credible flood levels, enhanced operator instructions and increased stocks of sand bags have also increased resilience at the two sites. 28 Flooding hazards and resilience will continue to be reviewed as part of future Periodic Safety Reviews (PSR). The work undertaken and described by Magnox Ltd. (Ref. 18) was an acceptable response to IR-10 and ONR therefore considers the Recommendation closed Recommendation IR This recommendation states: The UK nuclear industry should ensure that safety cases for new sites for multiple reactors adequately demonstrate the capability for dealing with multiple serious concurrent events induced by extreme off-site hazards. 30 Magnox Ltd. agreed with the recommendation and noted that ONR s expectations with respect to IR-11 specifically related to new build facilities. However, they considered it prudent to consider the existing Magnox Ltd. sites that neighbour EDF Nuclear Generation Ltd. (NGL) sites; namely Dungeness, Hinkley Point, Hunterston and Sizewell. Magnox Ltd. s other sites (Wylfa, Oldbury, Chapelcross, Bradwell, Berkeley and Trawsfynydd) are all single site locations for which IR-11 has no relevance. 31 Guidance indicates that it is considered good practice for existing sites to consider the impact of serious concurrent events at adjacent sites. Magnox Ltd. has Office for Nuclear Regulation Page 14 of 53

15 confirmed that agreements are in place between licensees for mutual strategic cooperation and that arrangements are exercised and demonstrated as part of the national emergency exercise programme. 32 The guidance states that IR-11 also applies to existing reactor licensees whose current sites are adjacent to a proposed new site. Whilst new reactors are proposed at Wylfa and Sizewell they are several years away from operation by which time the Magnox Ltd reactors at Wylfa and Sizewell are likely to have been defuelled. Whilst this point has not been specifically addressed by the licensee, given the timescales to new reactors operating on these sites ONR does not regard this as a significant omission. 33 No further work is proposed by Magnox Ltd. in response to IR-11. ONR agrees with this position and considers the recommendation closed Recommendation IR This recommendation states: The UK nuclear industry should ensure the adequacy of any new spent fuel strategies compared with the expectations in the Safety Assessment Principles of passive safety and good engineering practice. 35 This Recommendation was accepted by Magnox Ltd. as being applicable to them. However, only Wylfa and the defueling sites at Oldbury and Sizewell A are considered under this recommendation as all other Magnox Ltd. sites are now defueled. 36 Magnox Ltd. fuel is currently only present on the Oldbury and Wylfa sites. As such Magnox Ltd. has not produced any new spent fuel strategies. However, the resilience of the facilities, at these stations, for managing spent fuel (i.e. the fuel route, including the spent fuel ponds and in Wylfa s case the dry fuel stores) has been reviewed as a part of Magnox Ltd s response to the Fukushima accident (Refs. 23, 24 and 25). 37 In most cases existing resilience provisions were found (after site specific review) to be adequate. Nonetheless the improvements in the spent fuel area were implemented. This included complete re-structuring and revision of emergency and severe accident procedures and development of new fuel route and radioactive waste accident management guidelines across the sites, new pond filling lines and depth indicators at Oldbury and Sizewell A, CCTV to allow pond conditions to be observed at Sizewell A and the provision at Oldbury of four containers of site specific emergency equipment including equipment to seal or to minimise leakage from the spent fuel ponds following a beyond design basis event. 38 In addition prudent measures have been implemented to increase the back-up capability for essential functions such as the provision of additional stand-alone generators and pumps. Stocks of diesel and petrol to power such equipment have also been increased. Such equipment would be available to power (amongst other systems) essential fuel pond safety functions. 39 Magnox Ltd. has not revised its spent fuel strategy given the remaining life of the single operational reactor at Wylfa and the state of defueling at Oldbury. However, a comprehensive and well structured study, seeking improvements, has been carried out that takes account of engineering good practice. Improvements made as a result of the study are robust and pragmatic whilst other suggested improvements have good underpinning arguments as to why they have not been implemented. ONR is content that the Magnox Ltd. is not pursuing further work in the context of IR-12 and that all work in progress can be monitored to completion via ONR s normal regulatory interactions and site inspections. ONR considers Recommendation IR-12 closed. Office for Nuclear Regulation Page 15 of 53

16 3.2.6 Recommendation IR This recommendation states: The UK nuclear industry should review the plant and site layouts of existing plants and any proposed new designs to ensure that safety systems and their essential supplies and controls have adequate robustness against severe flooding and other extreme external events. 41 Magnox Ltd. accepted the finding and acknowledged that it was relevant to them. Magnox Ltd. has looked at resilience of sites to beyond design basis events by conducting a number of hazard-based workshops to examine possible hazards, safety requirements, and the resources needed to meet these requirements. Further site-specific resilience reviews were then undertaken taking into account the position in lifecycle at each site. 42 As a result of these workshops, opportunities for enhancing resilience against severe flooding and other extreme events were identified and implemented. Plant protection was enhanced against flooding at both Trawsfynydd and Oldbury as described in IR A list of examples of enhancements is provided in Ref. 1 and includes, for all sites, the provision of satellite phones, radiation monitoring cones, and an equipment container stocked with relevant items. Individual sites have implemented further resilience enhancements in accordance with the individual level of risk. 44 Magnox Ltd. noted that some of the planned enhancements have yet to be implemented. These are: Completion of work to replace a fuel oil storage tank at Wylfa Confirmation by ONR of enhancement to the pond water level monitoring systems at Sizewell A 45 Magnox Ltd. proposes to undertake these two on-going work items as part of its normal business. Both activities are scheduled for completion by September ONR accepts the Magnox Ltd. response for IR-13 and subject to the completion of the two remaining work items considers the Recommendation closed Recommendation IR This recommendation states: The UK nuclear indu stry should e nsure that t he design o f new spent fuel st orage ponds close to reactors minimises the need for bottom penetrations and lines that are prone to siphoning faults. Any that are necessary should be as robust to faults as the ponds themselves. 47 Magnox Ltd. accepted the recommendation and acknowledged that it was relevant to them. However, it is noted that Magnox Ltd. has restricted the response to the spent fuel pool at Oldbury that contains fuel. This is considered to be a practical approach as these sites are likely to represent the Licensee s principal hazard in the context of spent fuel storage ponds when compared to other defueled decommissioning sites. Spent fuel at Wylfa is exclusively stored in dry storage cells and as such IR-14 is not applicable to Wylfa. In addition, Ref. 1 makes the very clear statement that Magnox Ltd. will not be building any new spent fuel storage ponds. 48 After a review described in Ref. 1 Magnox Ltd. concluded that there are no physical means by which siphoning from the Oldbury fuel storage ponds could affect the shielding or cooling of the stored fuel. At Sizewell A failure of in-service or redundant underwater penetrations or pipework associated with either pond recirculation or Office for Nuclear Regulation Page 16 of 53

17 Caesium removal would still leave the fuel adequately water covered for shielding purposes.. 49 Enhancements to control and instrumentation resilience have been introduced at Oldbury. These are considered to be reasonably practical improvements to the site s existing plant monitoring capability that will enable remote assessment of pond water levels. The use of redundant passive pond water depth indicators should provide an effective means of improving the site s capability in the management of beyond design basis faults that may affect spent fuel ponds. Similarly, the improvements made to the plant information systems and instrumentation equipment that is associated with spent fuel ponds at Sizewell A will enhance the ability of the site to respond effectively to faults in the ponds building. 50 ONR s opinion is that the licensee has demonstrated (via clear arguments) that neither of its remaining operational spent fuel ponds at Sizewell A or Oldbury pose a threat of loss of pond water, via pond penetrations, to an extent where the safety functions of fuel shielding and fuel cooling would be compromised. Practical improvements to resilience of control and instrumentation equipment have also been undertaken; hence ONR accepts that the licensee has no additional work to do with respect to IR-14. Recommendation 1: ONR should inspect, as part of its routine regulatory business the implementation of measures to enhance the resilience of pond water level monitoring systems at Sizewell A Recommendation IR This recommendation states: Once detailed information becomes available on the performance of concrete, other structures and equipment, the UK n uclear industry should consider an y implications for improved understanding of the relevant design and analyses. 52 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd. takes part in a collaborative panel of technical specialists in civil engineering and external hazards, together with Sellafield Limited and EDF- NGL. The panel meets approximately twice per year and will continue to do so for the foreseeable future. The purpose is to review external hazards and the design of safety-related nuclear engineering structures. Magnox Ltd. will identify and evaluate those findings relevant to the seismic performance of its plants. However, Magnox Ltd. expects the relevance of these findings to be limited due to the lifecycle position of each of its plants and the diminishing nuclear and radiological risk levels on Magnox Ltd sites. 53 Although investigations are ongoing, current information suggests that structures, systems and components performed well at the Fukushima Dai-ichi and Dai-ni sites during the March 2011 earthquake. This is based on extensive walk-downs and assessments on the accessible parts of the plants. However, the full picture is not yet available and more information is likely to come to light as more areas of the Daiichi plant become accessible. 54 Magnox Ltd. will continue to engage with the panel of technical specialists as part of a cross-industry technical exchange forum. This is on-going work that will be undertaken as part of normal business. Although further work may be required pending the release of further information ONR accepts the Magnox Ltd. response to date, the commitment to undertake further work if necessary and the closure of the Recommendation Recommendation IR This Recommendation states: Office for Nuclear Regulation Page 17 of 53

18 When considering the recommen dations in t his report t he UK nuclear industry should consider them in the light of all extrem e hazards, particularly for plant layout and design of safety related plant. 56 Magnox Ltd. has indicated that the details of addressing this Recommendation are provided in the response to IR-13. The essence of this recommendation is that all external events should be considered, not just seismic and flooding. To address IR- 13, Magnox Ltd. held a series of workshops which have been reported and referenced. These workshops were attended by a range of personnel i.e. Site and Central Engineering engineers and Safety Case experts. Work lists arising from the workshops were drawn up for each site and resulted in a substantial programme of resilience enhancements across the fleet. A description of the enhancements is provided in the Magnox Ltd. Report (Ref. 1) and a subset of these are summarised in this report under IR-9 and IR-13. Additionally, the response to IR-13 indicates that all extreme hazards have been considered. 57 Magnox Ltd. provided a concise description of what was achieved in their response to this Recommendation and the description is considered appropriate by ONR. ONR considers the Recommendation closed Recommendation IR This Recommendation states: The UK nuclear indust ry should u ndertake fur ther work with the National Grid to establish th e robustness and pote ntial una vailability of off site el ectrical sup plies under severe hazard conditions. 59 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd SQEPs have reviewed the National Grid Electrical Transmission (NGET) report and sentenced (Ref. 26) each of the ten considerations of the working group report for each of their sites, fuelled and de-fuelled. In doing so, it has considered firstly the applicability of the recommendation to itself and then, if there is practical benefit, whether this could be delivered before any hazard on site is reduced such that the recommendation is no longer applicable. Magnox Ltd. reports that none of these sites make any safety case claims on off-site electrical systems to support essential safety systems. 60 Exploration and testing of communications with NGET during future emergency exercises is vital to demonstrate that any arrangements in place are sufficiently robust and understood to deliver their objectives. Magnox Ltd has acknowledged this and confirmed that Magnox Ltd and NGET intend to undertake a joint exercise during 2014 to test the lines of communication and methods of working together, to deliver a safe conclusion. ONR considers this to be a positive action in ensuring that both parties understand the types of issues that could arise in such an event. Recommendation 2: ONR should include the remaining work identified by Magnox Ltd. related to IR-17, IR-22, IR-23, IR-24, STF-3 and STF-16 within the scope of its normal business, especially for LC-10 (Training) and LC-11 (Emergency arrangements). 61 Given the lack of reliance on off-site power supplies and the commitments captured in Recommendation 2 ONR is content that no further work needs to be carried out under IR-17, with the exception of any learning points gained from activities linked to Recommendation 2. ONR is content that Recommendation IR-17 can be closed Recommendation IR This recommendation states: Office for Nuclear Regulation Page 18 of 53

19 The UK nu clear indust ry should r eview any need for the provision of additiona l, diverse m eans of providing robu st sufficient ly long-ter m independent electrical supplies on sites, reflecting the loss of availabilit y of off-site electrica l supplies under severe con ditions. This should be considere d along with Reco mmendation IR-8 within the wider context of "on-site resilience" 63 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd. notes that electrical supplies are not essential for post trip cooling on a pressurised reactor. This is in part due to the availability of prime mover driven boiler feed pumps and the ability for natural circulation to support cooling for a significant time until a limited amount of boiler feed could be established. 64 Given the operational status of Wylfa, it is recognised that loss of electrical supplies would prevent operation of the stand still seals leading to a small depressurisation leak. It is noted that as well as the existing ability to manually pump these closed, the station already had the provision to connect a portable generator external to the building to operate the electric pump. However, additional cabling has now been procured to enable the temporary generator to be located at a significant distance from the gas circulator hall and connected to an external connection point. This is a positive action given the experience at Fukushima where debris restricted access on site. 65 In addition to the existing portable generators Magnox Ltd concluded that it was not viable to increase the level of on site fixed generator installations at its locations. This was based on the remaining life of the operational station together with the reducing risk as plant is first shutdown and then defueled. 66 For the Wylfa site, Magnox Ltd. has chosen to provide an addition diesel bulk storage tank. This is based on the vulnerability of the site to loss of offsite power events and the relatively remote location of the site. 67 For the defuelled sites, where any requirement for electrical supplies is a significant period of time after the event, Magnox has chosen to procure additional generators to power tools, lighting and ventilation units for debris vaults. 68 Magnox Ltd. has followed a structured and documented process to assess diverse means of providing robust sufficiently long-term independent electrical supplies on site, which has highlighted potential benefits (Ref ). These benefits have been delivered and as a result on site resilience has been enhanced. ONR agrees with Magnox Ltd s view that no further work is required to address IR Recommendation IR This Recommendation states: The UK nu clear industr y should re view the ne ed for, and if required, t he ability t o provide lon ger term co olant supplies to nucle ar sites in t he UK in th e event of a severe off-site disruption, considering whether further on-site supplies or greater offsite capab ility is ne eded. This relates to bot h carbon d ioxide and fresh water supplies, and for existing and proposed new plants. 70 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Only the sites at Oldbury and Wylfa require coolant supplies as all other reactors in the Magnox Ltd. fleet are now defuelled (Note; Sizewell A pond is addressed by IR-20). 71 Magnox Ltd held a number of hazard-based workshops specifically looking at the resilience of sites to beyond design basis events. These workshops included the adequacy of the coolant supplies at Wylfa and Oldbury and resulted in further Office for Nuclear Regulation Page 19 of 53

20 resilience reviews (Refs. 44 and 47). These reviews resulted in a number of resilience enhancements being identified for each site. 72 With respect to supplies of CO 2 Magnox Ltd has reviewed the requirements for Wylfa. The Wylfa review has concluded that there are sufficient stocks of CO 2 on site and that procurement of additional supplies is not warranted. For on site water supplies at Wylfa Ref. 47 confirms that the Tertiary Feed tanks are seismically qualified and have sufficient capacity for supplying feed to the one operating reactor for longer than 72 hours. It is also noted that these tanks can be topped up from the town s water system if it is available. Usage of a road tanker to transport water to site and an additional source of fresh water from a nearby lake has also been identified (Figure 9). 73 In the case of Oldbury, Magnox Ltd reports that only intermittent boiler water feed (~ every 2 weeks) is needed and that suitable and sufficient sources of water are provided by back-up feed system water tanks, the town s water main reservoir and an engineered borehole. 74 ONR judges that Magnox Ltd has made a proportionate response to IR-19 and considers the Recommendation closed Recommendation IR This Recommendation states: The UK nu clear indust ry should re view the sit e contingen cy plans f or pond water make up under severe accident conditions to see whether they can an d should be enhanced given the experience at Fukushima. 76 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them; however it is only relevant to the Oldbury and Sizewell A sites. These are the only sites that have ponds containing spent fuel since Wylfa has a dry fuel store. 77 The inventory of the ponds is well below capacity and decay rates low enough that temperature rises due to loss of cooling would not be expected to rise by more than 1ºC per day and would equilibrate well below the pond water boiling point. Therefore, significant loss of pond water will not occur by evaporation or boiling. Siphoning mechanisms cannot lead to a significant loss of water from the ponds (see Recommendation IR-14). Significant water loss can only occur as result of a severe mechanical failure of the pond structure. 78 Enhancements have been made at both Oldbury and Sizewell A. There are slight differences due to the different pond locations with respect to ground level but these include: Installation of a new seismically qualified filling line at Oldbury allowing water to be added directly to the ponds by gravity feed alone if necessary from a point external to the building; Installation of a new seismically qualified fuel pond filling line at Sizewell A enabling water to be pumped directly into the pond from a diverse source, together with diesel driven and electric submersible pumps and connectors; Provision of site-specific emergency equipment, stored in a resilient location, including equipment to seal or minimise leakage from the ponds following a beyond design basis event; Provision of specific accident management guidelines for accidents affecting the fuel route including pond damage leading to loss of pond water (see STF-16); Enhancements to address the capability to measure the depth of water remaining in the pond following an event. Office for Nuclear Regulation Page 20 of 53

21 79 The reviews and subsequent enhancements undertaken by Magnox Ltd for IR-20 are proportionate and also help to satisfy aspects of IR-14 and STF-16. No further work is planned by Magnox Ltd. to address IR-20 and ONR considers that this Recommendation can be closed Recommendation IR This Recommendation states: The UK nuclear industry should review the ventilation and venting route s for nuclear facilities wh ere signif icant concentr ations of co mbustible g ases m ay be flowing or accumulating to determine whether more should be done to protect them. 81 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd has completed a comprehensive review (Ref. 27) of its facilities in relation to the potential for generating combustible and/or toxic gases. The review includes Hydrogen generation from fuel element debris vaults; Hydrogen generation from Magnox dissolution plants; Hydrogen generation resulting from water ingress into a Magnox reactor; Hydrogen generation from spent fuel ponds; Carbon Monoxide generation under severe accident conditions. 82 Magnox Ltd. has concluded that existing measures to minimise the generation of combustible or toxic gases and their accumulation are sufficient, although some procedural improvements have been identified. Magnox Ltd. also reports that certain severe and highly improbable accident conditions specific to the operating reactor at Wylfa could lead to the evolution of flammable or explosive concentrations of combustible gases or the evolution of toxic gases. Over and above the measures in place to prevent such conditions occurring Magnox Ltd. has concluded that no practical enhancements have been identified to mitigate such scenarios. For such cases the Severe Accident Guidelines (SAGs) have been revised to make operators aware of the risks associated with combustible and toxic gases under specific accident conditions. 83 ONR accepts that Magnox Ltd. has completed a comprehensive review of the potential for its facilities to generate combustible and/or toxic gases and that no reasonably practical enhancements have been identified other than improvements to some operating procedures and the Severe Accident Guidelines. ONR supports Magnox Ltd s decision to close Recommendation IR Recommendation IR This Recommendation states: The UK nuclear indu stry should review the provision on- site of em ergency control, instrumentation and communications in light of the circumstances of t he Fukushima accident including long timescales, wide spread on and off- site disru ption, and the environment on-site associated with a severe accident. 85 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox has provided a clear description of the role of the emergency control centres at Wylfa. There is a site based Emergency Control Centre (ECC), an alternate ECC located off-site on higher ground and the option to use a training facility located off-site as a third ECC if the two ECCs are not tenable. Whilst none of these ECCs are seismically qualified they are located at some height above sea level such that there is a low potential for flooding from a beyond design basis external Office for Nuclear Regulation Page 21 of 53

22 event. Seismic qualification of the ECCs was not seen as practical given the remaining operating life and ONR accepts this position. 86 The Magnox Ltd. response to IR-22 has focussed on making reasonably practicable enhancements to the emergency facilities. These have included repairing the air handling unit damper for the Central Control Room and improving the air tightness of the room. Dose rate and airborne contamination monitors have been installed to provide an alarm in the event of elevated radiological conditions within the CCR. However, the installation of monitoring equipment to detect explosive or toxic gases in the CCR or Remote Emergency Indication Centre (REIC) has been declared by Magnox Ltd. to be not reasonably practicable, (Ref. 28). Taking into account the response for IR 21 ONR accepts this position. 87 A key tenet for informing and making an effective incident response is the availability of accurate plant status information. The REIC is seismically qualified but is located at the same elevation as the main reactor site and thus would be vulnerable to the same wind and flood events that could potentially affect the main reactor. To ensure that the emergency indication function is preserved at Wylfa, an alternate totally diverse monitoring system has been installed. This communicates key reactor parameters, via independently powered wireless transmitters (Figure 12), to the beyond design basis equipment (BDBE) compound (Figure 13). The design and configuration of the diverse system generally conforms to the categorisation and classification designated for severe accident instrumentation in accordance with ONR expectations. A contingency plan is in preparation to provide instruction on set up and operation of the ECC at the compound. A proof of concept exercise is also planned at Wylfa in September This forms part of the normal business emergency exercise work as described in Recommendation In addition to the enhancements at Wylfa Magnox Ltd has reviewed resilience of onsite ECCs, instrumentation and communication systems at all of its sites and introduced reasonably practicable improvements that are commensurate with current plant status, particularly at its decommissioning sites. This includes enhancements to control centres at the Oldbury and Sizewell A sites. 89 The Magnox Ltd. response to IR-22 aligns with ONR s expectations and therefore closure of the recommendation is supported Recommendation IR This Recommendation states: The UK nuclear indu stry, in conjunction wit h other organisations as necessa ry, should review the robustness of necessary off-site com munications for severe accidents involving widespread disruption. 91 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. A report examining the resilience of emergency communications at Wylfa has been prepared, (Ref 29). This concluded that for design basis events, there is sufficient technically diverse telecommunications solutions that provide a resilient means of communicating essential information to responding personnel located onand off-site during an emergency. 92 For a beyond design basis event, where all installed communication systems could be lost, communication would continue to be available to the off-site stakeholders using satellite phones and available on-site by using radio or runners to co-ordinate the response activities. The Wylfa ECC has been provided with an installed satellite system that allows calls to be made from inside the ECC. 93 The recommendations from Ref. 29 are being considered by Magnox Ltd. The implementation of the communications review recommendations will be taken forward at Wylfa as normal business. ONR considers that two of the Office for Nuclear Regulation Page 22 of 53

23 recommendations from Ref. 29 should be taken forward as a priority. These form Recommendations 3 and 4 from this report: Recommendation 3: Provision of CCR access to a fixed satellite system. This would enable the CCR to notify the Strategic Coordinating Centre (SCC) that an offsite nuclear emergency has occurred and to provide the initial advice on countermeasures that should be employed to protect the public. This would include provision of a 3 rd satellite phone and docking station at the BDBE compound to provide off-site communication in event of loss of the ECC and Alternate ECC. Recommendation 4: Provide portable radio relay systems, and training in the use and limitations of radio operation in back-to-back mode. A loss of site radio repeater function will significantly reduce the operating range of hand-held radios and increase congestion levels of radio traffic. To ensure that the CCR and ECC staff can continue to manage movement of staff and coordinate response activities effectively, site should consider providing portable radio relay systems, and training in the use and limitations of radios in back-to-back mode. 94 The demonstration of Recommendations 3 and 4 should take place during the proof of concept exercise described under IR-22 and captured in Recommendation 2. Subject to these demonstrations ONR considers that Magnox Ltd. has provided an adequate response against IR-23 in order for the Recommendation to be closed Recommendation IR This Recommendation states: The UK nuclear indu stry shou ld review existing se vere accident contingency arrangements and training, givin g particula r consider ation to the physica l, organisational, behavio ural, em otional and cultural aspect s for worke rs having t o take action s on-site, especially ove r long periods. This sh ould take a ccount of th e impact of using contractors for some aspects o n-site such as maintenance and their possible response. 96 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd. has reviewed, revised and developed the SAGs and SBERGs (Refs. 30 and 31) and developed new fuel route and radioactive waste accident management guidelines for both operating and decommissioning sites. These revisions have taken due account of human factors aspects. 97 Magnox Ltd. has furnished all sites with additional emergency response equipment to facilitate specific actions or for more general post-event recovery actions. The equipment in combination with the revised procedures assists in the sealing of breaches in the reactor pressure vessel and the management of gas circulation and boiler feed to secure reactor cooling. Training arrangements have been reviewed and updated where necessary. Existing command and control training has been judged adequate for emergency controllers to manage incidents at Magnox sites. However, it has been recognised that additional training is required to alert and equip staff to deal with stress and fatigue potentially arising in large-scale incidents. Consequently existing training packages for ECs will be augmented to cover these aspects. 98 The role of contractors in emergency conditions has been reviewed. All contractors undergo induction training and this includes reinforcement of expected behaviours if an emergency is declared, including mustering and evacuation if instructed. 99 On-site personnel welfare arrangements during emergency conditions have been reviewed by Magnox Ltd. s Occupational Health Department; and each site has enhanced its existing provisions where appropriate. Additionally Magnox Ltd. has arranged provision for post-event care with an external specialist service provider. Office for Nuclear Regulation Page 23 of 53

24 This includes post-trauma care, psychological and psychiatric support. Magnox Ltd. s corporate communications team has taken part in national discussions considering wider stakeholder communications during an extended emergency. The team is part of the national UK strategy for emergency communications. 100 The ability to get sufficient staff to the Wylfa site is not considered an issue as the local topography around the site is not particularly low-lying. In addition the majority of staff lives on the Isle of Anglesey and Wylfa has sufficient 4 x 4 vehicles for transporting personnel to / from site if required. 101 The Licensee considers that these items are now closed on the basis that analysis work is complete and further enhancement modifications and training can best be taken forwards as part of normal business. This position aligns with ONR s expectations and therefore closure of the Recommendation is supported Recommendation IR This Recommendation states: The UK nuclear indu stry shou ld review, an d if necessary extend, analysis o f accident sequences for long-term severe accid ents. This should identif y appropriate repair and recovery str ategies to t he point at which a stable state is achieved, identifying any enhanced requirements for central stocks of equipm ent and logistical support. 103 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them and has focussed the response on the single remaining operating reactor at Wylfa; the only site where a significant off-site release of radioactive material is considered credible. 104 The work undertaken in response to IR-25 is largely covered elsewhere in relevant sections. For example, reviews of site self-sufficiency and consequent enhancements to the provision of emergency equipment have been completed in response to IR-8, the revision of the SBERGs and the SAGs is covered by Magnox Ltd s response to STF-16 and potential long term severe accident sequences have been investigated as part of the response to FR-4 which relates to Level 2 PSA. 105 On the basis of the work completed to review the existing analyses, the development of the Level 2 Probabilistic Safety Assessment and subsequent revision and enhancements of the SBERGs and the SAGs Magnox Ltd has provided an appropriate and proportionate response to IR-25 and ONR considers the Recommendation closed Recommendation FR This Recommendation states: Safety Case: All nucle ar site lice nsees shou ld give app ropriate and consiste nt priority to completing Periodic Safe ty Reviews (PSR) to the required standards and timescales, and to im plementing identif ied reaso nably practicable p lant improvements. 107 Magnox Ltd. and its predecessors, as operators of the UK Fleet of Magnox reactors, have undertaken periodic reviews of safety. Currently all Magnox reactors, apart from Wylfa Reactor 1, are permanently shutdown and are at various stages of preparation for care and maintenance. 108 Magnox Ltd. is actively engaged in developing appropriate formats for PSRs for permanently shutdown reactors, and are taking due cognisance of the organisational changes within Magnox Ltd. and the implications these will have for PSRs. ONR will continue to interact with Magnox Ltd. in respect of the development and delivery of the PSRs appropriate to the state of the reactor being reviewed. Office for Nuclear Regulation Page 24 of 53

25 109 Magnox Ltd. consider this Recommendation closed on the basis that they remain fully committed to the PSR process, giving appropriate priority to completing such reviews to the appropriate standards and timescales, including the timely implementation of reasonably practicable plant improvements. Magnox Ltd. s proposal is in accordance with ONR s expectations and therefore closure of the Recommendation is supported Recommendation FR This Recommendation states: The UK nuclear indu stry should e nsure that structures, systems and com ponents needed for managing and controllin g actions in response t o an accide nt, includ ing plant contro l room s, o n-site em ergency contr ol centres and off-site e mergency centres, ar e adequate ly prote cted against hazards th at could a ffect se veral simultaneously. 111 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd has provided a clear explanation of the role of the emergency control centres with a particular focus on Wylfa and Oldbury and this is considered appropriate. The actions taken following site resilience reviews includes the proportionate provision of new command and control capabilities for all sites. 112 ONR notes that Magnox Ltd. does not intend to provide back up facilities for plant control; however it is unlikely that provision of such capability would be practicable within the lifetime of the one operating reactor. As described under IR-22 construction of a seismically qualified / hardened ECC or CCR would not be practicable within the remaining lifetime of the one operating reactor at Wylfa. The Magnox Ltd. response has therefore focussed on making reasonably practicable enhancements to the existing emergency control centres and their back up facilities. ONR considers that Magnox Ltd s. response is broadly in accord with ONR s expectations, based on its high level statements and supports the closure of FR Recommendation FR This Recommendation states: Structures, systems and com ponents needed for managing and controlling action s in response to an accident, including plant control rooms, on-site emergency control centres and off-site emergency cen tres, should be capable of operating adequately in the conditions, and f or the durat ion, for which they cou ld be need ed, inclu ding possible severe accident conditions. 114 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd. does not maintain hardened emergency facilities for post accident command and control. Instead the operating philosophy is that the command and control function is performed wherever information can be collated and decisions made and promulgated (Ref 1). If a facility becomes untenable or unavailable for any reason then the function will be taken to a different location. The resilience of command and control function is therefore a matter of resilience of information provision and its communication rather than location of an emergency facility. 115 Application of the Magnox Ltd. emergency operating philosophy to the circumstances of a severe accident at Wylfa (the only site for which a severe accident is a credible fault consequence), that involves widespread disruption on and off site, would potentially result in the loss of all non qualified emergency centres and installed communication infrastructure. This would place reliance on diverse communications such as satellite phones, portable radios and runners to inform the Central Emergency Control Centre (CESC) and ensure the continued operation of the Office for Nuclear Regulation Page 25 of 53

26 emergency response function at Wylfa. This reliance is covered in Recommendation Reliance would also be placed on communications between emergency personnel responding on site (IR-23) and the provision of sufficient welfare supplies, health physics and radiological protection (IR-8). These aspects are detailed under the respective Recommendations. 117 ONR judges that there is likely to be sufficient remaining emergency arrangements infrastructure to manage and control actions in response to a severe accident that involves widespread disruption on-site. As such the Magnox Ltd. response is adequate and the Recommendation can be closed subject to the undertaking of Recommendations 3 and 4, which will be monitored in normal business Recommendation FR This Recommendation states: The nucle ar industry should ensure that adequate Level 2 Probabilist ic Safe ty Analyses (PSA) are provided for al l nuclear fa cilities that could have a ccidents with significant offsite consequences and use the results to inform further consideration of severe accident management measures. The PSAs should consider a full range of external events including beyond design basis events and extended mission times. 119 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd. has not developed a full scope level 2 PSA in response to recommendation FR-4. ONR recognises that it would have been impracticable for a complete full scope level 2 PSA and associated analyses to be undertaken on a timescale consistent with delivering safety benefit before the end of operation at Wylfa (the only site for which a severe accident is a credible fault consequence). 120 Magnox Ltd. has developed and performed a suitable methodology for a limited scope level 2 PSA for Wylfa (Ref. 33). The outcome of the level 2 PSA work is to inform and underpin improved severe accident management measures at Wylfa power station. As such, a wide ranging list of potential improvements for the Wylfa accident management guidance has been identified and these improvements have been incorporated into the response for STF ONR considers that recommendation FR-4 has been adequately addressed and that all further work associated with the level 2 PSA outcomes should be moved to normal business under STF 16 (as described in Recommendation 2). Subject to the undertaking of Recommendation 2 in normal business Recommendation FR-4 can be closed Recommendation FR This Recommendation states: The nuclear industry with others sh ould review available techniques for estimating radioactive source terms and undertake research to test the practicability of providing real-time inf ormation on the basic characteristics of radioactive rele ases to the environment to the responsible off -site authorities, takin g account of t he range of conditions that may exist on and off the site. 123 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Magnox Ltd. has produced a report that deals with source terms related to the single operating reactor at Wylfa (Ref. 32). The report states that the Hazard Identification Risk Evaluation (HIRE) assessments produced for each of the Magnox Ltd. sites show there are no "reasonably foreseeable faults at any of the Magnox Ltd. sites, which would require any off-site countermeasures to be considered beyond the Detailed Emergency Planning Zone (DEPZ). Office for Nuclear Regulation Page 26 of 53

27 124 Credible but beyond reasonably foreseeable events such as activity releases sufficient to require consideration of countermeasures significantly beyond the DEPZ were identified. These would require irradiated fuel elements with clad damage at temperatures only possible at a site with an operating reactor. Reference 30 identifies a set of source terms representing a range of beyond reasonably foreseeable emergencies at Wylfa together with views on how and when these should be used. ONR considers that this approach is a credible response and meets the intent of FR Although Magnox Ltd s review meets the requirements for FR-6, wider work to fully understand the user requirements for the source terms is currently underway across industry and Magnox Ltd. are participating in this work. ONR supports Magnox Ltd s position to close FR-6 subject to their continuing participation in the cross industry working groups Recommendation FR This Recommendation states: The UK nuclear industry should cont inue to promote sustained high levels of safety culture am ongst all its e mployees, making use of the Nati onal Skills Academy fo r Nuclear and other schemes that promote nuclear professionalism. 127 Magnox Ltd. accepted the Recommendation and acknowledged that it was relevant to them. Nuclear professionalism plays a prominent role in the Magnox Ltd. programme of work and all staff within the company have received human performance training to raise awareness of error avoidance techniques. The training is based on internationally-recognised strategies and techniques to reduce and minimise the consequences and severity of errors. Senior managers are also trained to ensure director-level understanding. 128 The promotion of nuclear professionalism is a key outcome of Magnox Ltd. s engagement with National Skills Academy for Nuclear. Magnox Ltd. has held discussions with other UK nuclear licensees to plan measures that make use of the National Skills Academy for Nuclear and other schemes that promote nuclear professionalism. These discussions have resulted in a cross-industry project to develop a nuclear industry training framework that will drive training excellence and provide a framework to enhance and maintain nuclear professionalism across the sector. 129 ONR considers that the Magnox Ltd. response to this Recommendation is adequate. The work undertaken in this response will continue as part of normal business. Given that no additional measures need to be put in place to ensure the continuation of this work ONR considers the recommendation closed. 3.3 Stress Test Findings Stress Test Finding STF This Stress Test Finding states: The nuclear industry should establish a resear ch programme to review the Seism ic Hazard Working Party ( SHWP) methodology a gainst the latest appro aches. This should include a gap an alysis comparing the SHWP methodology with more recent approaches such as t hose developed by th e Senior Seism ic Hazard Analysis Committee (SSHAC). 131 Magnox Ltd. accepted the finding and acknowledged that it is relevant to them. Magnox Ltd. is part of a cross-industry response to address this Finding. ONR recognises that Magnox Ltd. has only one remaining operational reactor site at Wylfa and this is expected to close in The usefulness of work on this Finding is Office for Nuclear Regulation Page 27 of 53

28 therefore limited as there would not be sufficient time to perform relevant studies before the reactor reaches its operational life, even if it were ALARP to do so. In addition, Magnox Ltd. undertook a comprehensive re-analysis of seismic hazard for the Wylfa site in 2004 as part of the PSR. Although issues were raised with the adequacy of this re-analysis, it does reinforce the existing design basis and provides additional confidence that the DBE (design basis earthquake) is robust. 132 ONR finds the Magnox Ltd. response for STF-2 coupled with the reasonably practicable resilience improvements described for other Recommendations and Findings appropriate and proportionate. It meets the intent of this Finding and is accepted by ONR, hence ONR considers STF-2 as closed Stress Test Finding STF The Stress Finding States: Licensees should undertake a further review of the totality of the req uired action s from operat ors when th ey are claimed in mitigation within external hazards safe ty cases. This should also extend into beyond design basis events as appropriate. 134 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them. Magnox Ltd. has completed a proof of concept assessment for each site in order to demonstrate that robust measures are in place for managing emergency equipment. This also ensures that additional emergency equipment provided as part of the response to the Fukushima accident remains in a state of readiness for deployment. ONR supports this approach. 135 The Magnox Ltd. response to STF-3 rightly focuses on Wylfa. The Wylfa safety cases were substantiated by specific human factors assessments as part of the Wylfa Periodic Safety Review (PSR) completed in These assessments took account of operator ability to carry out claimed actions based on design basis external fault consequences. These assessments have been reviewed and it is judged that little benefit would be gained from repeating the PSR qualitative and quantitative Human Factors (HF) assessments of operator actions. 136 Newly-developed Emergency Operating Procedures (EOPs) have also been produced. These EOPs were developed as part of a suite of documents to define and describe actions to be taken by operators for managing beyond design basis accidents at Wylfa. The assessment of the EOPs is qualitative. It includes consideration of whether the required actions could be taken under postulated degraded conditions, including those that might arise from external hazards. The proof of concept exercise at Wylfa scheduled for September 2014 will demonstrate the use of the newly-developed EOPs 137 ONR accepts the Magnox Ltd. response for STF-3 and supports its closure Stress Test Finding STF The Stress Test Finding states: Licensees should und ertake a further syst ematic review of the potential f or seismically-induced fire which m ay disrupt t he availa bility of safet y-significant structures, systems and components (SSC) in t he seismic safety ca se and access plant areas. 139 Magnox Ltd. accepted the finding and acknowledged that it is relevant to them. Magnox Ltd. provided a clear explanation of the work that has been done at all sites with emphasis on Wylfa. This is due to the significant post-seismic event active reactor cooling requirements at the site and this is considered an appropriate approach. Office for Nuclear Regulation Page 28 of 53

29 140 The assessment at Wylfa (Ref. 34) has been undertaken in accordance with appropriate guidance from the Electric Power Research Institute (EPRI) in the United States by appropriate SQEP and appears from the description given to have been a wide-ranging and comprehensive assessment. In addition, appropriate action has been taken to address the assessment finding. The Magnox Ltd. approach for other sites is proportionate and reasonable. 141 The Magnox response coupled with the reasonably practicable improvements it has implemented is an appropriate and proportionate response. It meets the intent of this Finding and closure is accepted by ONR Stress Test Finding STF The Stress Test Finding states: Licensees should furth er review the margins for all saf ety sign ificant structure s, systems and components (SSC), including coo ling ponds, in a structured system atic and com prehensive m anner to und erstand the beyond de sign basis sequence o f failure and any cliff edges that apply for all external hazards. 143 Magnox Ltd. accepted the finding and acknowledged that it is relevant to them. The emphasis has again been placed on Wylfa as the only Magnox Ltd. site where there is significant safety-related dependence on the integrity of the reactor pressure boundary. It is considered appropriate that the level of effort has been concentrated at Wylfa for this response. 144 Magnox Limited has reviewed the resilience of safety-significant structures, systems and components against external hazards as follows. The primary emphasis has been on reviewing the resilience of Wylfa. 145 Seismic margins analyses have been performed and reported for Wylfa and Oldbury. For the plant considered, Magnox Ltd. reported a margin of 174% for civil structures and a margin of 50% against the loss of essential safety systems (Ref. 1). In addition substantial resilience enhancements have been delivered for both sites. Of particular note is the new emergency equipment compound at Wylfa provisioned with back-up equipment to facilitate restoration of essential safety functions if required. The compound storage facilities have been designed to be lightweight so that potential collapse in an extreme seismic event would not prevent the use of the equipment. Additional resilience enhancements at both Wylfa and Oldbury have been listed and described in Ref Coastal flooding margins for Wylfa are relatively large and the likelihood of coastal flooding affecting safety related plant at Wylfa is therefore considered to be very low. Flooding resilience enhancements have been implemented at all Magnox Ltd. sites and have been reported. These include, at Wylfa, provision of a range of mobile and portable generators and supporting services for restoring electrical supplies if required. Additional resilience enhancements for all Magnox Ltd. sites have been listed and described in Ref The effects of extreme weather, including from combinations of coincident meteorological events, have been reviewed and reported. Considerable enhancements to the resilience against extreme weather have been implemented at Wylfa in recent years including strengthening of building envelopes to improve resistance to wind loading and overhaul of the storm water drainage system. A further layer of resilience has been specifically implemented post-fukushima, including a new emergency equipment compound. No margins were found at Wylfa that were below 3.0 metres with respect to flooding as the result of extreme weather for essential electrical systems or other safety related equipment. 148 ONR accepts that these conclusions are valid for Wylfa given the balance between extensive existing operating experience and limited remaining life. Office for Nuclear Regulation Page 29 of 53

30 149 For the other Magnox Ltd. sites, a description of the general approach to achieving failure resilience and defence in depth has been made. ONR has encouraged Magnox Ltd. to implement reasonably practicable safety improvements that should in general be straightforward measures with immediate benefit, with less focus on long-term study work (Ref. 35). Therefore, the resilience improvements described by Magnox Ltd. coupled with the description of its application of defence in depth is considered an adequate and proportionate response to STF-5 for its non-operational sites. 150 ONR considers that an adequate response has been given to STF-5 and supports the closure of the Finding Stress Test Finding STF The Stress Test Finding states: Licensees should review further th e margin to failure of the containm ent boundary and the point at which containm ent pressure boundary integrity is lost should be clearly esta blished f or the advan ced gas- cooled reacto rs (AGR) and Magnox stations. 152 Magnox Ltd. accepted the finding and acknowledged that it is relevant to them. Only one reactor at Wylfa remains operational and at pressure and Magnox Ltd. considers that this is the only site for which STF-6 remains relevant. ONR accepts this conclusion. 153 The review of the vulnerability of the reactor pressure boundary for Wylfa Reactor 1, as described in Ref. 1, is judged by ONR to meet the requirements of this Finding. In particular, the focus on improving small bore pipework resilience, including the pipework support systems, is considered appropriate because this is likely to be the limiting feature in terms of pressure boundary integrity. The seismic margins analysis performed and described within the response to STF-5 included small bore reactor pressure boundary pipework. The conclusion is that there are substantial margins to accommodate earthquake loadings that are more severe then the design basis event. 154 The response from Magnox Ltd. meets the intent of this Finding and is accepted; hence ONR considers the Finding closed Stress Test Finding STF This Stress Test Finding states: Licensees should undertake a more structured and systematic study of the potential for floodwater entry to b uildings containing safety significant structures, systems and components (SSC) from extreme rainfall and / or overtopping of sea defences. 156 Magnox Ltd. accepted the finding and acknowledged that it is relevant to them. Magnox Ltd. has chosen to focus the bulk of its response to this Finding on sites with remaining nuclear fuel (Wylfa and Oldbury). However, it has also completed a comprehensive review of the design basis flooding for all ten of its sites. ONR considers this an appropriate approach given the increased level of hazard potential when nuclear fuel remains on-site. The removal and passivation of the remaining radioactive material on the sites will steadily diminish the residual risks from beyond design basis flood events as the sites progress towards their planned care and maintenance condition. 157 The flooding review revealed that the design basis was undermined for Trawsfynydd and Oldbury (see Recommendation IR-10). Proportionate resilience enhancements have been implemented to reduce the already low risks posed by site flooding. Forward actions arising from this study are being taken forward as normal business. Office for Nuclear Regulation Page 30 of 53

31 158 Given the limited life of the operating reactor and the lower hazard at other sites the Magnox Ltd. response including the focus on sites housing nuclear fuel is an appropriate and proportionate response. It meets the intent of this Finding and is accepted by ONR for closure Stress Test Finding STF This Finding states: Licensees should fu rther invest igate the provision o f suitable event-qualified connection points to facilitate the reconnection of supplies to essential equipment for beyond design basis events. 160 Magnox Ltd. accepted the finding and acknowledged that it is relevant to them. For Wylfa, supply of clean boiler feed water has been prioritised. Whilst through the existing multiple electric and prime-mover driven pumps, there is defence in depth, Magnox Ltd. has chosen to procure six new portable pumps, any one of which is sufficient to supply the feed water requirements for one operating reactor. Alternative boiler connection points have been identified and connections procured and stored in resilient boxes local to the connection. Magnox Ltd. considers that making appropriate connections on the day is the most appropriate approach. This allows some flexibility for unforeseen events and also negates the need to await an outage before making the connection, which would limit the safety benefit for the remaining operating period of the reactor. 161 As described under IR-18 additional electrical generators have been provided for those sites with fuelled cores. Procedures have been developed for isolating and repowering circuits using identified connection points and alternative supply sources. Magnox Ltd. has chosen a strategy to identify multiple potential connection points, leaving the decision to the day based upon the extent of the event and any associated damage; they have chosen to identify those boards for connection and develop generic procedures for ad-hoc connection rather than install multiple planned points. ONR acknowledges that this approach gives added flexibility. 162 Magnox Ltd. has reviewed the provision of suitable connection points to facilitate the reconnection of supplies to essential equipment following beyond design basis events. Proportionate enhancements have been implemented across the Magnox Ltd. fleet; ONR is content with the response to address STF-8 and concurs with Magnox Ltd s view that no further work to address the Finding is required Stress Test Finding STF This Finding states: Licensees should furt her investig ate the enhancem ent of stocks of essential supplies (cooling water, fuel, carbon dioxide, et c.) and exten ding the aut onomy time of support system s (e.g. battery system s) that either provide esse ntial safety functions or support emergency arrangements. 164 Magnox Ltd. accepted the finding and acknowledged that it is relevant to them. This finding is related to IR-19 which specifically addresses water and carbon dioxide supplies. As with other Recommendations and Findings focus is centred on the operating reactor at Wylfa. Wylfa has numerous diesel fuel storage tanks associated with the various gas turbines and diesel engines and the fuel is cross-compatible with any safety-related plant. There are also two additional bowsers that have been procured for moving fuel around the site. Wylfa is in the process of recommissioning a 220,000 litre oil tank that supplies the main gas turbine generators to improve the resilience of fuel stocks. It is expected that this activity will be complete by September In addition, since the original reviews were done, one reactor has been permanently shutdown and the other is due to cease generation no later than Office for Nuclear Regulation Page 31 of 53

32 December The shutdown of each reactor will reduce the overall gas turbine generator loading which will in turn reduce the fuel consumption rate. ONR considers that this is a proactive action by Magnox Ltd. 165 ONR considers approaches taken at Oldbury and Wylfa, to identify potential switchboards to connect new portable generators an appropriate action. This affords flexibility through appropriately managed and controlled lists describing potential connection points and connection instructions. The documentation is held at the Emergency Control Centre. 166 No modifications are proposed at any site to the battery systems. However, ONR considers that given the primary focus following a loss of grid and reactor trip scenario is on establishing some boiler feed to support natural circulation of the carbon dioxide CO 2 gas, the decision not to modify battery systems is considered reasonable. 167 Since the defueled sites have no short or medium term requirement for electrical supplies, Magnox Ltd. has concluded that an enhancement to the stocks of essential supplies at these sites is not justifiable. ONR considers this reasonable noting that this decision has not precluded Magnox Ltd. from procuring additional portable generators and pumps for each of these sites to provide emergency team support such as lighting, small power and de-watering capabilities (Figure 14). 168 ONR judges that the actions taken by Magnox Ltd. in response to STF-9 are proportionate given the generating status of the Magnox Ltd. sites, especially noting that even those sites with no irradiated fuel onsite have received additional support generators and pumps. Subject to the completion of the fuel tank re-commissioning at Wylfa by September 2014 ONR considers this finding closed Stress Test Finding STF The Stress Test Finding states: Licensees should iden tify safety-significant pr ime mover-driven generators and pumps that use shared support systems (including batteries, fuel, water and oil) and should consider m odifying those pr ime movers systems to ensure they are capab le of being self-sufficient. 170 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them. Focus for this finding centred on Wylfa and Oldbury as all sites were identified by Magnox Ltd. to have no safety-significant prime-mover driven generators or pumps that use shared support systems. 171 For Wylfa, Magnox Ltd. identified a number of essential safety systems with a degree of shared systems, such as common bulk fuel or water feed tanks. Magnox Ltd. confirmed that consideration was given to improving the segregation within these systems. However, recognising the defence in depth that already exists through the gas turbine generators, electrical overlay generators, backup feed pumps and tertiary feed pumps together with the time that it would take to implement any modifications Magnox Ltd. concluded that there was insufficient benefit to be gained from additional modifications. Additional modifications would also introduce the added risk of other maintainability or operability issues over the short operating life of the plant. Given the other enhancements being implemented in the wider Fukushima response, ONR supports the Magnox Ltd. argument. 172 At Oldbury site, Magnox Ltd. identified only one safety significant prime-mover generator with shared supporting systems; the gas turbine generators. They identified the only shared aspect to this was the common building and all other aspects were independent. Magnox Ltd. again concluded that the time and Office for Nuclear Regulation Page 32 of 53

33 practicality of enhancing the building was outweighed by the ever decreasing requirement for emergency generation with cold reactors and defueling underway. 173 In mitigation at Wylfa and Oldbury, Magnox Ltd. has procured a number of portable generators, including 415V generators, that could be used to power up individual switchboards providing the associated infrastructure and loads remained intact following the severe event. 174 Overall, ONR considers that Magnox Ltd. has adequately identified any shared services on essential systems and given due consideration to segregating them further. ONR supports Magnox Ltd s conclusions that the modifications necessary to increase segregation are disproportionate to the safety benefit and would be unlikely to be fully realised before reactor shutdown and defueling have started Stress Test Finding STF The Stress Test Finding states: Licensees should further consider resilience improvements to equipment associated with the connection of the trans mission syste m to the es sential elect rical syst ems (EES) for severe events. 176 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them. Magnox Ltd. established a reasonable strategy to focus their efforts on further improving the resilience of the redundant and diverse systems on site given they have no direct control on the resilience of the UK transmission system. 177 An agreement is in place with the local Distribution Network Operator (DNO) and National Grid Electrical Transmission (NGET) to establish arrangements to backfeed Wylfa from the local distribution network should a prolonged loss of offsite power event occur. For Oldbury, the current plan will have the supply available at the station fence with connection to site once the decommissioning overlay scheme is installed. Although the grid supply point for the DNO supply is ultimately the same substation as the current 132kV connection, there is some diversity in the routing that provides some additional protection. 178 Magnox Ltd. has confirmed that the connections were designed, installed and have been maintained to at least the same requirements that NGET use and therefore do not propose any additional enhancements given that the capacity is bounded by the NGET resilience. 179 ONR considers that Magnox Ltd has adequately assessed the robustness of the connection between the transmission system and the essential electrical system to ensure it as least as robust as the equipment considered part of the transmission system. As such no further work in response to STF-11 is required Stress Test Finding STF The Stress Test Finding states: Magnox Ltd should assess the progressive loss of electrical systems on all aspects of the fuel route and address any implications. 181 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them. STF-12 was raised due to an omission by Magnox Ltd. to report fully the effects of a progressive loss of electrical supplies on the complete fuel route; a requirement of the European Council Stress Test methodology (Ref. 6). Magnox Ltd. undertook a Office for Nuclear Regulation Page 33 of 53

34 review that has now been formally documented in a report (Ref. 36) for all locations where nuclear fuel remains onsite. ONR has reviewed the report (Ref. 35) and considers that it logically and adequately considers the progressive loss of supply issue on the fuel route. The report makes no recommendations for enhancements and based on the conclusions of the report ONR supports this position and judges that no further work is required in response to STF Stress Test Finding STF The Stress Test Finding states: Magnox Ltd should d emonstrate that all rea sonably pra ctical m eans have bee n taken to ensure integrity of the fuel within the dry fuel stores in the extremely unlikely event of the natural draft air ducting becoming blocked. 183 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them. However, the Recommendation is specific to the dry fuel stores at Wylfa power station with all other Magnox Ltd. sites having ponds for on site spent fuel storage. 184 Magnox Ltd. considers that the only possible way the dry store fuel vents could become blocked is by flooding, and has procured additional pumps and generators to remove accumulation of water. It should be noted however that the likelihood of flooding is extremely low due to the vents elevation and surrounding gradient (i.e. a large beyond design basis margin is available). 185 ONR had enquired as to whether the accumulation of drifting snow had been considered for blockage of the dry store vents (Ref. 37). Magnox Ltd. made the case that it is unlikely that both vents could become blocked by drifting snow as they are facing opposite directions, providing separation. If they were to both become blocked, Magnox would have time (approximately 58 hours in the worst case scenario) to clear the vents manually. The response time is also applicable to a flooding scenario. 186 Although blockage of vents is seen as extremely unlikely Magnox Ltd. has considered blockage of the primary dry store cell cooling air inlet ducts as one of the scenarios covered by the new fuel route accident management guidelines that have been developed for Wylfa. This is part of the response to Stress Test Finding STF The Magnox Ltd. response to this Finding is considered reasonable and is accepted by ONR Stress Test Finding STF The Stress Test Finding states: Licensees should confi rm the exte nt to which resilience enhancements are to b e made to existing equipment and systems that are currently installed at nuclear power plants. Information should be pro vided on the equipment and systems that m ay be affected an d the nature of the resilience enha ncements, i ncluding int erconnectivity with mobile back up equipment. 189 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them. This is a wide-ranging Stress Test Finding and responses to IRs 8,10,13,19,20,22 and 23, FRs 2 and 3 and STFs 4,5,7,8,9,10 and 11 cover aspects of the response for this Finding. 190 Magnox Ltd. has provided a clear description of the functional outcome of this Finding. A summary of the enhancements performed has been provided in Ref. 1. The enhancements arose from a series of workshops for each relevant area proportionate to radiological risk at each site. The list of external hazards and the Office for Nuclear Regulation Page 34 of 53

35 resulting resilience enhancements considered are wide-ranging and take into account the remaining risks at each site in a proportionate way. 191 A series of reports has been completed for each site, and as part of normal business interventions ONR will assess these to ascertain whether resilience enhancement of existing equipment has been satisfactorily addressed. 192 The Magnox Ltd. response to this Finding is considered reasonable; it meets the intent of this Finding, is accepted and the finding considered closed Stress Test Finding STF The Stress Test Finding states: Licensees should com plete the va rious review s that they have highlig hted so that ONR can a ssess their proposals and associated timescales. These reviews sho uld look in det ail at on-sit e e mergency facilities and arrange ments, off-site facilitie s, facilities for rem ote indication of plant status, co mmunication systems, contents and location of beyond design basis co ntainers and the adequacy of any arrange ments necessary to get people and equipment on to and around sit e under severe accident conditions. Any change s to arrang ements and equipm ent will require appropriate training and exercising. 194 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them. STF-15 is related to many other Recommendations and Findings and the responses to IRs 8, 13, 14, 17, 18, 19, 22, 23, 24, 25, FR 3 and STFs 3, 8, 9, 10, 11, 16 and 83 are all relevant in addressing the intent of STF Magnox has completed various reviews and these are documented in the site summary reports for each site (Refs ). The content of the reports combined with the responses to the Recommendations and Findings described above satisfy the intent of STF-15 and ONR is therefore content that this finding can be closed Stress Test Finding STF The Stress Test Finding states: Licensees should review the sympto m-based e mergency response guideline s (SBERG) and severe accident guidelines (SAG) taking into account im provements to the understanding of severe accid ent progression, pheno mena and t he equip ment available to mitigate severe accident. This revie w should also take into account th e fuel route. Once completed, appropriate training and exercising should be arranged. 197 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them in the case of the single operating reactor at Wylfa. The reactors at Oldbury and Sizewell A have been shutdown for a considerable period of time and are being defuelled. All other reactors in the Magnox Ltd. fleet are completely defuelled and passively safe. Magnox Ltd s position is that an accident of the severity addressed by SBERGs and SAGs is only credible at Wylfa. ONR agrees with this position and the intent of the new accident management guidelines for defueling and decommissioning sites. 198 Magnox Ltd. has completed comprehensive reviews and revision of the SBERGs and SAGs (Refs 30 and 31). It has also developed a new set of Emergency Operating Procedures (EOPs) that complement particularly the SBERGs. The EOPs provide information to support the implementation and use of additional Back-Up Equipment that has been provided in response to various other Recommendations and Stress test Findings. Magnox Ltd. has additionally developed new Fuel Route Accident Management Guidelines (FRAMGs) for use in event of an incident with the potential to lead to an off-site radiological release. The production of the FRAMGs also satisfies the intent of STF-83. Office for Nuclear Regulation Page 35 of 53

36 199 Review of the Wylfa SBERGs and SAGs included refresher training for emergency and assistant emergency controllers and other technical support staff to increase awareness in the advice and intended use. In addition a review of the documentation was undertaken by a specialist contractor and a HF specific review completed to ensure usability of the SAGs and SBERGs. The limited scope L2 PSA study that was undertaken in response to Recommendation FR-4 also provided input into the revised SAGs and SBERGs. 200 The outcome of the reviews allowed Magnox Ltd. to make improvements to the documentation to ensure that information is technically correct and matches the plant configuration; has enhanced clarity and usability; follows international best practice; provides enhanced decision support and prioritisation; and gives greater clarity between the roles and advice within the SBERGs and SAGs. 201 Equipment necessary to mitigate a severe accident at Wylfa has been provided within the BDBE equipment compound. The use of this equipment in conjunction with the SBERGs has been verified (Ref 48). 202 A separate programme of work has been undertaken to develop FRAMGs for Wylfa, Oldbury and Sizewell A for potential fuel route accidents. Although there is much commonality the guidance does need to account for the plant differences between the sites. Exercising of FRAMGs will take place on the applicable sites as part of the normal programme of site emergency exercises. 203 Magnox Ltd. has undertaken an extensive review and revision programme of their accident management guidance and made appropriate changes together with introducing new documentation that is more appropriate for sites that are in defueling or decommissioning operations. ONR accepts Magnox Ltd s response to STF-16 and considers that no further work is necessary other than the on going exercise and training programme (see Recommendation 2) that exists as part of normal business Stress Test Finding STF The Stress Test Finding states: Licensees should further review the systems required to support long term claims on the pre-stressed concrete pressure vessel cont ainment capability in se vere accident conditions. 205 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to them. Magnox Ltd s review (Ref. 28) has identified that at Wylfa, even without the pressure vessel cooling system no action would be required to protect the concrete pressure vessel itself for a period of approximately 2 months. However, under unmitigated severe accident conditions it is reported that the reactor containment safety function could be threatened on a timescale of a few days by heating and failure of steel penetrations that pass through the containment structure. 206 In response to this Magnox Ltd has considered emergency actions to protect the reactor containment, including the concrete pressure vessel and penetrations as part of the limited-scope Level 2 PSA produced in response to FR-4. This has resulted in revised SBERGs containing advice on controlling reactor temperatures and pressure in beyond design basis conditions to mitigate the possibility of containment failure. In addition, the updated SAGs are reported to incorporate revised advice on actions that will assist in preventing, delaying and mitigating containment boundary failure. ONR is content that the reviews and revisions undertaken are adequate and have received appropriate involvement of SQEPs. ONR is content that Magnox Ltd. considers this item closed Stress Test Finding STF The Stress Test Finding states: Office for Nuclear Regulation Page 36 of 53

37 Magnox Ltd should ca rry out a re view of the design ba sis and m argins ava ilable against ext ernal hazards at each decommi ssioning sit e to ensure adequate provisions are in place throughout the decommi ssioning process commensurate with the remaining radiological hazard. 208 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to its decommissioning sites. The safety cases for specific decommissioning operations already meet the intent of this finding. Magnox Ltd. have committed to address this finding for legacy structures in the course of updating relevant safety assessments within the declared Periodic Safety Review programme as part of normal business. This has already been considered as part of the Hinkley Point A PSR that was submitted in March 2014 (Ref. 49) Stress Test Finding STF The Stress Test Finding states: Magnox Ltd should review, update and issue revised severe accide nt guidelines in the light of changing hazard at decommissioning sites; the g uidelines should include human performance / welfare issues and availability of equipment located in beyond design basis containers. 210 Magnox Ltd. accepted the Finding and acknowledged that it is relevant to its decommissioning sites. Fuelled sites are also considered but are covered under a different STF (STF-16). 211 A description of the production of the FRAMGs is given under the response for STF- 16. Magnox Ltd has developed accident management guidelines for accident scenarios involving intermediate and low level waste for decommissioning sites. Like the FRAMGs, SBERGs and SAGs these guidelines also take account of human performance and welfare issues with HF specific reviews of the relevant documentation being undertaken as part of the process. As such ONR accepts that the intent of STF-83 has been met and considers the finding closed. 4 CONCLUSI ONS 212 This report presents the findings of ONR s review of the report titled: Summary of the Magnox Ltd. Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami (Ref. 1). 213 Magnox Ltd has acknowledged the applicability of all of the Chief Inspectors Recommendations relevant to the nuclear industry (noting that Magnox Ltd does not believe all Recommendations are fully applicable to all of its sites due to the varying stages of the sites within their lifecycles) and nearly all of the Stress Test Findings focused on nuclear power generating facilities (the only exception was a Finding relating to Sizewell B operated by EDF NGL). 214 Where relevant initial analyses and scoping studies were performed to identify the forward programmes of work. This included a number of technical workshops, which led to site specific work lists that provided an overview of planned or implemented work across Magnox Ltd s sites (Ref ). The work lists were submitted to ONR. The enhancements described in the site-specific work programmes can be considered to have made a significant contribution to improving safety for beyond design basis accidents/events. ONR acknowledges that considerable effort on providing enhanced resilience, enhanced essential supplies and additional back up equipment has been undertaken. Office for Nuclear Regulation Page 37 of 53

38 215 Magnox Ltd s. initial response included a number of prudent improvements that were straightforward measures which provided genuine safety benefit. Examples of early safety improvements implemented included: Increased CO 2 and diesel fuel stocks on-sites, well above those required by operating rules existing at the time; A new diverse pond water emergency filling line at Oldbury and Sizewell A (see Figure 1 & 2); Provision of backup feedwater/fire pumps on-sites to provide further defence indepth (see Figures 3 & 4); Development and implementation of improved training in respect of the Symptom Based Emergency Response Guidelines (SBERGs) and Severe Accident Management Guidelines (SAGs); Additional stocks of essential equipment (e.g. basic tools, flash lights etc.) onsites stored in diverse locations (see Figures 5-8); The purchase of a water tanker for transport of water from a nearby fresh water source to site (Wylfa) (see Figure 9). 216 Further longer term work then took place that included: Improving the extent of resilience enhancements to Control & Instrumentation (C&I) systems and equipment associated with plant condition monitoring, and secondary control capabilities in emergency facilities. Site enhancements and modifications against seismic, flood and fire hazards. Increased resilience of fuel storage ponds to extreme events. This included additional lines for pond refilling (Figures 1 and 2) following a severe event. This includes suitable equipment for leak repair and associated processes being put in place. Review of guidance in beyond design basis operating instructions as well as the adequacy of training and exercise arrangements together with implementation of improvements to enhance human performance during extreme conditions. Procurement of a range of containerised back-up equipment to support sites in the management of a beyond design basis accident, or an event (Figures 5, 7 and 8). The containerised back-up equipment includes mobile diesel generators (Figure 10) and isolation transformers that can be used to supply existing systems and equipment at sites. 217 To conclude, ONR is broadly satisfied with the claims, arguments and evidence laid down within the Summary of the Magnox Ltd. Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami (Ref. 1). Practical enhancements have been undertaken to the plant and procedures. This has been done with a focus on timely improvements given the remaining operational life of the single reactor at Wylfa. With this in mind Magnox Ltd. has not embarked on lengthy analysis, or on plant improvements with long implementation times. ONR fully supports this approach and considers that the work undertaken in response to events at Fukushima is appropriate, proportionate and that Magnox Ltd s view that work to address the Recommendations and Findings is complete is valid. ONR is therefore content that the Recommendations and Findings can be closed. This is subject to completion of: Installation and commissioning of the already manufactured fuel oil tank at Wylfa by September Office for Nuclear Regulation Page 38 of 53

39 Demonstration of back up equipment procured (including that described under Recommendations 3 and 4) in an emergency exercise at Wylfa during September REC OMMENDATIONS 218 The project assessment report recommends that: Recommendation 1: ONR should inspect, as part of its routine regulatory business the implementation of measures to enhance the resilience of pond water level monitoring systems at Sizewell A. Recommendation 2: ONR should include the remaining work identified by Magnox Ltd. related to IR-17, IR-22, IR-23, IR-24, STF-3 and STF-16 within the scope of its normal business, especially for LC-10 (Training) and LC-11 (Emergency arrangements). Recommendation 3: Provision of CCR access to a fixed satellite system at Wylfa. This would enable the CCR to notify the Strategic Coordinating Centre (SCC) that an off-site nuclear emergency has occurred and to provide the initial advice on countermeasures that should be employed to protect the public. This would include a 3 rd satellite phone and docking station is provided at the BDBE compound to provide off-site communication in event of loss of the ECC and Alternate ECC. Recommendation 4: Provide portable radio relay systems, and training in the use and limitations of radio operation in back-to-back mode at Wylfa. A loss of site radio repeater function will significantly reduce the operating range of hand-held radios and increase congestion levels of radio traffic. To ensure that the CCR and ECC staff can continue to manage movement of staff and coordinate response activities effectively, site should consider providing portable radio relay systems, and training in the use and limitations of radios in back-to-back mode. ONR expects Recommendations 2, 3 and 4 to be closed out after the emergency exercise planned at Wylfa in September 2014, Whilst Recommendation 1 should be complete by the end of Office for Nuclear Regulation Page 39 of 53

40 6 REFERENCES 1 Magnox Ltd. Report: Summary of the Magnox Ltd. Limited Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami, TRIM 2013/ ONR Report: Japanese earthquake and tsunami: Implications for the UK nuclear industry - Final Report. 11 October ONR Report: European Council Stress Tests for UK Nuclear Power Plants, National Final Report. December ONR Report: Stress Tests for UK non-power Generating Nuclear Facilities, Final Report. December Magnox Ltd. response to the Interim Report Recommendations, July 2011, TRIM. 2011/ ONR Report: Japanese earthquake and tsunami: Implementing the lessons for the UK's nuclear industry pdf 7 European Nuclear Safety Regulators Group: Stress tests specification March Assessment of Magnox Ltd s Final Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami External Hazards, ONR-CNRP-AR , TRIM 2014/ Assessment of Magnox Ltd s Final Response to Lessons Learned from the Accident at Fukushima C&I Aspects of the Chief Inspectors Recommendations IR-14, IR-22, IR-23, FR-3 and Stress Test Findings STF-14, STF-15, ONR-CNRP-AR , TRIM 2014/ Assessment of Magnox Ltd s Final Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami Emergency Arrangements, ONR-CNRP-AR , TRIM 2014/ Electrical Engineering Assessment of Magnox Response to Fukushima, ONR-DFW-AR , TRIM 2014/ Assessment of Magnox Ltd s Final Response to Lessons Learned from the Accident at Fukushima Covering the Chief Inspectors Recommendations IR-11, IR-19, IR-21, IR-25 and Stress Test Findings STF-9, STF-16, STF-17, ONR-CNRP-AR , TRIM 2014/ ONR-CNRP-AR , Assessment of Magnox Ltd s Final Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami Human Factors, TRIM 2014/ Assessment of Magnox Ltd. Ltd s Final Response to Lessons Learned from the March 2011 Japanese Earthquake and Tsunami ONR Chief Inspector s Report Interim Recommendations IR-12 and IR-14, ONR-DFW-AR , TRIM 2014/ Assessment of Magnox Ltd s response to Fukushima recommendation FR-4: Level 2 Probabilistic Safety Analysis (PSA), ONR-FR-AR , TRIM: 2014/ Magnox Ltd. response to the Interim Report recommendations, July 2011, TRIM 2011/ Mission Report - The Great East Japan Earthquake Expert Mission - IAEA International Fact Finding Expert Mission of the Fukushima Dai-ichi NPP Accident Following the Great East Japan Earthquake and Tsunami, Tokyo, Fukushima Dai-ichi NPP, Fukushima Dai-ni NPP and Tokai Dai-ni NPP, Japan, 24 May 2 June 2011, June iaea.org/mtcd/meetings/pdfplus/2011/cn200/documentation/cn200_final- Fukushima-Mission_Report.pdf. 18 Office for Nuclear Regulation Page 40 of 53

41 ONR Report: Japanese Earthquake and tsunami: Implementing the lessons for the UK s nuclear industry, October ONR-FR-PAR : Fukushima Recommendation, Stress Test Findings and Considerations: Overall Review of Magnox Ltd. responses, TRIM 2012/ CX Technical Department Note 1160 Issue 1, April 41 Office for Nuclear Regulation Page 41 of 53

42 Office for Nuclear Regulation Page 42 of 53

43 Figure 1: Emergency Pond Water Filling Line at Oldbury Office for Nuclear Regulation Page 43 of 53

44 Figure 2: Emergency Spent Fuel Pond Filling Line at Sizewell A Figure 3: Diesel Driven Fire Pumps at Wylfa Office for Nuclear Regulation Page 44 of 53

45 Figure 4: Diverse Flood Resilient Boiler Feed Pump at Oldbury Figure 5: Beyond Design Basis Emergency Equipment Containers at Oldbury Office for Nuclear Regulation Page 45 of 53

46 Figure 6: Enhanced Stocks of Staff Welfare Supplies at Oldbury Figure 7: Beyond Design Basis Emergency Equipment Containers at Sizewell A Office for Nuclear Regulation Page 46 of 53

47 Figure 8: Beyond Design Basis Emergency Equipment Containers Supplied to All Sites Figure 9: Road Tanker for Emergency Water Transportation at Wylfa Office for Nuclear Regulation Page 47 of 53

48 Figure 10: Emergency Diesel Generators at Wylfa Office for Nuclear Regulation Page 48 of 53

49 Figure 11: Satellite Telephones Supplied to All Sites Office for Nuclear Regulation Page 49 of 53

50 Figure 12: Alternative Emergency Reactor Monitoring System at Wylfa Office for Nuclear Regulation Page 50 of 53

51 Figure 13: Beyond Design Basis Emergency Equipment Compound at Wylfa Figure 14: Submersible Pumps at Wylfa Office for Nuclear Regulation Page 51 of 53

52 Figure 15: Location of Magnox Limited Sites Office for Nuclear Regulation Page 52 of 53