European Nuclear Stress Test

Transcription

1 European Nuclear Stress Test - Peer Review Process and Results - 9. St. Galler Energietagung Oskar Grözinger Symposium : The Fukushima accident and the future of nuclear energy in Europe Den Haag, Content 1. Overview - Stress Test and Peer Review process 2. Main results and recommendations - European level 3. Results - Borssele NPP 4. Follow-up - action plans 5. Conclusions 1

2 European Council Request after Fukushima 11 March: Fukushima accident March: European Council Request Review of all EU plants in the light of lessons learned from Fukushima Stress test to be developed by ENSREG* and the European Commission with the support of WENRA** Assessments subject to a peer review *ENSREG: European Nuclear Safety Regulators Group **WENRA: Western European Nuclear Regulators Association What was the Nuclear Stress Test? Comprehensive risk and safety assessment of all 143 nuclear power plants in the EU and the plants of Ukraine and Switzerland (Σ >160 NPPs in 17 countries) using EU wide criteria based on the so called ENSREG Specification; organized by ENSREG with support of the European Commission; peer review was managed by a special peer review Board. 2

3 Stress Test shall give answers to the Fukushima concerns The Stress Test was a 'new' way of looking at safety. Instead of showing how safe the plants are, was asked: What does bring plants into trouble? Did we properly take into account uncertainties of all potential external hazards? Are our plants robust enough and are the safety margins big enough? Are we able to cope even with extremely low probability events? New viewpoints brought new insights. Objectives of the Nuclear Stress Test? Learning from what happened in Japan, to prevent a similar accident from happening in Europe: Evaluation of the behaviour of the nuclear power plants in postulated extreme situations Verification of the preventive and mitigative measures Assessment of the robustness of nuclear power plants, including beyond their design bases, to identify relevant safety margins and whether the safety margins used in their licensing are sufficient to cover unexpected events. safety relevant cliff edge effects* *cliff edge: a sudden large variation in plant conditions in response to a small variation in an input 3

4 Topic 1 - Natural Hazards earthquake, flooding and extreme weather conditions Tsunami 2011/3/11 Topic 2 - Loss of Safety Functions Assumed scenarios: loss of off-site power station black out loss of ultimate heat sink 4

5 Topic 3 - Severe Accident Management to prevent the escalation of an event into a severe accident; to mitigate the consequences of a severe accident and to achieve a long term safe stable state. Main Steps June 1 st October 31 th : Assessment of plants by operators requested by national Regulators October 31 th January 1 st : Review of operators assessments by national Regulators National report to the European Commission January 1 st April 26 th : Peer Review of national reports 5

6 Peer Review Participants European Commission Nuclear EU Member States (15) Belgium Bulgaria Czech Republic Finland France about 80 experts Germany from 28 countries Hungary Lithuania Netherlands Romania Slovakia Slovenia Sweden Spain United Kingdom Non Nuclear EU Member States (6) Austria Denmark Ireland Italy Luxembourg Poland Nuclear Non EU Member States (2) Switzerland Ukraine Observers IAEA Canada Croatia Japan UAE USA Peer Review Process Topical Review of national reports topic by topic Desktop review for a month (January 2012) Full two weeks seminar in Luxemburg (February) 51 review sessions conducted Country review by peers (March) 6 teams 4-5 days in each country One site visit in each country selected by the review team 6

7 Output 17 country reports: Country specific conclusions and recommendations Main report: Final conclusions and recommendations at European level All reports were approved by ENSREG on April 26 th 2012 Public Outreach Public meetings January 17 th on Peer Review process May 8 th on Peer Review results Internet - ENSREG-website all National and Peer Review reports; comprehensive information on the Stress Test and Peer Review process; conclusions and slides of the public meetings Stakeholders could post questions for the Peer Review 7

8 Content 1. Overview - Stress Test and Peer Review process 2. Main results and recommendations - European level 3. Results - Borssele NPP 4. Follow-up - action plans 5. Conclusions Main conclusions The peer review identified: 4 main recommendations and many detailed findings included in the main report and the 17 country reports. Significant steps taken in all European countries to further improve safety of nuclear power plants. 8

9 Assessment of robustness Topic 1 (external hazards): evaluation of margins and cliff edge effects generally not consistent with ENSREG specification resulted in recommendation 1 Topic 2 and 3 (loss of safety functions and accident management): safety margins and cliff-edge effect determination was generally in line with ENSREG specification 19 June 2012 Rec. 1: Guidance on assessment of natural hazards and margins The peer review Board recommended that, WENRA*, involving the best available expertise from Europe, develop guidance on natural hazards assessments, including earthquake, flooding and extreme weather conditions, as well as corresponding guidance on the assessment of margins beyond the design basis and cliff-edge effects. *WENRA: Western European Nuclear Regulators Association 19 June

10 Periodic safety review Peer review demonstrated effectiveness of Periodic Safety Reviews* (PSRs) To maintain and improve safety and robustness of the plants * Periodic safety review is a systematic reassessment of the safety of a facility carried out at regular intervals (mostly 10 years) to deal with the cumulative effects of ageing, modifications, operating experience, technical developments and siting aspects, and aimed at ensuring a high level of safety throughout the service life of the facility. 19 June 2012 Rec. 2: Periodic safety review The peer review Board recommended that, ENSREG should underline the importance of periodic safety reviews. In particular, ENSREG should highlight the necessity to re-evaluate natural hazards and relevant plant provisions as often as appropriate, but at least every 10 years. 19 June

11 Containment integrity Fukushima disaster highlighted once again the importance of the containment function Containment is the last barrier to protect people and the environment against radioactive releases Issue has been already considered as follow-up of previous accidents and possible improvements have been already identified 19 June 2012 Rec. 3: Containment integrity The peer review Board recommended that, the recognized measures to protect the containment integrity should be urgently implemented 19 June

12 Accidents resulting from natural hazards and limiting their consequences Fukushima highlighted as well the necessity of preventive measures as: Bunkered equipment including instrumentation and communication means Mobile equipment stored in locations protected against extreme natural hazards Emergency response centers designed against extreme natural hazards and radioactive releases Rescue teams and equipment rapidly available to support the local operator 19 June 2012 Rec. 4: Accidents from natural hazards and limiting their consequences The peer review Board recommended that, measures allowing prevention of accidents and limitation of their consequences in case of extreme natural hazards should be implemented. 19 June

13 Content 1. Overview - Stress Test and Peer Review process 2. Main results and recommendations - European level 3. Results - Borssele NPP 4. Follow-up - action plans 5. Conclusions Results Borssele Results from the peer review and here especially the visit to the Netherlands 12 th 15 th March 2012 and the NPP: 1. Results are presented in order of the 3 topics of the stress test; 2. Appraisal of Borssele in the light of the 4 main recommendations on EU level, which cover the important lessons learned from Fukushima All findings and results are also documented in detail in the country report and the main report, which are published on the ENSREG-website. 13

14 Results: General Attitudes Strong commitment of the regulator and the operator to improve nuclear safety; Committed and dedicated technical staff in the regulatory body and in the organization of the operator; Effectiveness of activities in enhancing safety; Openness and transparency in communication to the public. Clear safety and transparency enhancing influence of the Borssele Covenant and the Borssele Benchmark Committee Results: Natural Hazards Earthquake - Weak features Present Design Basis Earthquake (DBE) corresponds with a Peak Ground Acceleration (PGA) of 0,6 / 0,75 m/s 2 to a return frequency of less than 10-4 per year. The return frequency is in compliance with international good practices. But the PGA is below the IAEA s suggested minimum of 0,1g at free field. Will be solved in the frame of the next Periodic Safety Review by a new seismic assessment including a new DBE value of at least 0.1g PGA at free field. 14

15 Results: Natural Hazards Flooding - Weak features / Considerations If an extreme flooding occurs and a failure of dyke happens, then: Possible loss of communication-systems The dykes belong to the national dyke system, which protects the country. There are no dykes specifically protecting the NPP. It should be considered to make sure that this procedure is compliant with IAEA guidance which requests: Permanent barriers to protect the site from a Design Basis Flood (DBF) and redundant means to protect the plant against flooding. Results: Natural Hazards Flooding - Strong features / good practices A new risk analysis on flooding, including failure mechanisms of dykes, will be prepared in the ongoing Periodic Safety Review. The Design Basis Flood (DBF) is associated to 1 million years return period, without considering the national dikes network 15

16 Results: Natural Hazards Earthquake and Flooding Strong features / good practices Realized: Bunker Concept including a seismic resistance of 0.1g = beyond current DBE Scheduled: Establishing of an additional Emergency Response Center Results: Loss of Safety Functions Power supply - Weak features The use of the mobile Emergency Diesel Generator (EDG) which is currently available on-site might be problematic, as: Its moving requires off-site support (truck). Moving and connection to the emergency grid 2 would take some 6 hours and the potential site flooding might render it useless. 16

17 Results: Loss of Safety Functions Power supply - Strong features / good practices Possible operation of the plant in house-load regime Redundant 2-level emergency power supply grids with emergency diesel generators (EDG) Emergency grid 1 3 EDG - 2 of 3 EDG are air-cooled Emergency grid 2 2 EDG - bunkered solution Connections to the neighboring coal fired power station with possibility of supplying power to either the Emergency grid 1 or 2 Results: Severe Accident Management Weak features Not all equipment necessary for Severe Accident Management is subjected to routine maintenance/inspection Severe Accident Management Guidelines (SAMG) should to be developed also specific for the Spent Fuel Pool (SFP). 17

18 Results: Severe Accident Management Strong features / good practices Borssele has Severe Accident Management Guidelines (SAMGs) for all operational states including shutdown. The licensee has been very proactive, implementing them far faster than in many other nations reviewed. The scale of emergency exercises at Borssele is unusually large by international standards one recent national exercise involved 1000 people. Already installed: Passive Autocatalytic Recombiners (PARs) to reduce the hydrogen concentration to prevent hydrogen/oxigen explosions in case of a core melt accident. Containment Venting System for a targeted pressure reduction inside the containment Results: Severe Accident Management Strong features / good practices Borssele has used a full scope Level 3 Probabilistic Safety Assessment* (PSA) for deriving its severe accident management strategies. Many nations reviewed are still developing Level 2 PSAs. * Probabilistic Safety Assessment (PSA) is a comprehensive, structured approach identifying failure scenarios, constituting a mathematical tool for deriving numerical estimates of risk. Three levels of PSA are generally recognized: Level 1 comprises the assessment of plant failures leading to determination of the frequency of core damage. Level 2 includes the assessment of containment response, leading to the determination of frequencies of failure of the containment and release to the environment of a given percentage of the reactor core s inventory of radionuclides. Level 3 includes the assessment of off-site consequences, leading to estimates of public risks. 18

19 EU level Recommendations Natural Hazards Natural hazards as: earthquake, flooding and extreme weather conditions are reassessed during the ongoing Periodic Safety Review. This is an effective measure for continuous improvement The flooding assessments show significant margins beyond the design bases. Conclusion: Borssele is sufficiently prepared against natural hazards EU level Recommendations Periodic safety reviews 10-yearly Periodic Safety Reviews (PSR) since 1986 full scope living Probabilistic Safety Assessment (PSA) which is updated yearly. Plant modifications and updated failure data are included in the PSA model. Effective risk monitor PSR and PSA are part of the continuous improvement process. Conclusion: Leading role within Europe in respect to PSR and PSA 19

20 EU level Recommendations Containment integrity Borssele NPP has Severe Accident Management guidelines to decrease the primary pressure after a core melt is equipped with Passive Autocatalytic Recombiners (PARs) to reduce hydrogen risks inside the containment and Containment Venting line with a wet scrubbing filter system for a targeted pressure reduction Conclusion: High standard in respect to containment integrity EU level Recommendations Accidents from natural hazards and limiting their consequences Comprehensive backfitting measures in the last 25 years by introduction of the bunker concept, which is a two-train -bunker protected against high flood levels and earthquakes; Expansion of the emergency power system to 3 x 100% in different locations around the plant (principle of spatial separation); Separation of safety systems to realize independency between trains Measures for further improvements proposed by the licensee : Emergency Response Centre; Protected storage facilities for portable equipment Conclusion: High standard to prevent and limit natural hazards 20

21 Content 1. Overview - Stress Tests and Peer Review process 2. Main results and recommendations - European level 3. Results - Borssele NPP 4. Follow-up - action plans 5. Conclusions Follow-up strategy 26 April 2012 ENSREG and European Commission Approved the peer review reports and declared the stress test beeing terminated; Decided that follow-up activities would occur through action plans Each national regulator has to develop and make public a national action plan 21

22 National Action Plans - Content The national action plans will provide an update on the implementation status of: National regulator conclusions from their national stress tests as documented in their national reports; Recommendations in the ENSREG main and country peer review reports; Additional recommendations arising from the Convention on Nuclear Safety - meeting in August and, Additional activities derived from national reviews and related decisions. National Action Plans Schedule National Regulators develop their National Action Plans by the end of 2012 ENSREG discusses the National Action Plans in a peer review workshop in spring June

23 Content 1. Overview - Stress Tests and Peer Review process 2. Main results and recommendations - European level 3. Results - Borssele NPP 4. Follow-up - action plans 5. Conclusions Conclusions European level The European nuclear stress test was a challenge and very laborious. Only the peer reviews required resources of about 500 men-year. showed a new quality of transparency and openness in nuclear affairs and strengthened the independence of nuclear regulators; was a great step forward to improve safety in all European NPPs; contributed to give Europe a leading role in promoting nuclear safety world-wide. Public interest in nuclear safety increased and will go on also in the future and keep regulators alert and force licensees to improve safety of their plants. 23

24 Conclusions Borssele NPP Borssele is one of the older NPPs in Europa. But promoted by the regulator the licensee has consequently and continously backfitted and modernized its plant. This counts not only for the design but also for the operation and emergency processes. In this context it is noteworthy that proactively modern review and assessment tools as Periodic Safety Reviews and a living Probabilistic Safety Assessment have been developed and used. The review team saw a nuclear power plant, which is responsibly operated and well prepared to prevent severe accidents and to manage them, stressed the importance of continuing to maintain such high standards, acknowledged the safety enhancing influence of the Borssele Covenant and the Borssele Benchmark Committee Thank you for your attention 24