OFFICIAL. Magnox Swarf Storage Silo (MSSS) Risk and Hazard Reduction Programme

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1 Title of document Magnox Swarf Storage Silo (MSSS) Risk and Hazard Reduction Programme Application for Agreement to Commence Installation and Inactive Commissioning of SEP2 and 1 Mobile Caves in MSSS Project Assessment Report ONR-SEL-PAR Revision 1 January 2016 Template Ref: ONR-DOC-TEMP-005 Revision 11 Page 1 of 12

2 Office for Nuclear Regulation, 2016 If you wish to reuse this information visit for details. Published 01/16 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 12

3 EXECUTIVE SUMMARY Magnox Swarf Storage Silo (MSSS) Risk and Hazard Reduction Programme Permission Requested 1. The Licensee requested ONR's agreement via arrangements made under Licence Condition 22(1) to commence installation followed by inactive commissioning of Silo Emptying Plant (SEP)2 and SEP1 mobile caves in the Magnox Swarf Storage Silo (MSSS). Background 2. The Magnox Swarf Storage Silo (MSSS) is a legacy facility that represents one of the largest nuclear hazards in the United Kingdom. The facility comprises 22 vertical concrete silos, partially below ground level, that were in active use between 1964 and 1991 to store fuel cladding arising from the decanning of Magnox fuel elements. The ageing silo compartments contain a large inventory of radioactive waste (a mixture of intermediate level solid and liquid waste, and miscellaneous beta gamma waste). This modification relates to installation of equipment to facilitate waste retrievals from the original building and first extension only. 3. A recent assessment carried out by ONR concluded that the overall risk arising from the ageing MSSS facility is intolerable and the risk continues to increase significantly with time as the building structure ages. A significant structural failure would have major radiological consequences; therefore, retrieval of the waste is a national priority that must be dealt with promptly. ONR is focussed on ensuring that Sellafield Ltd progresses retrievals and subsequent decommissioning as quickly as is safely practicable whilst maintaining continued safe storage of the MSSS radioactive inventory. 4. Removal of the radioactive inventory will be achieved using three machines known as the Silo Emptying Plant (SEP), which will remotely and mechanically retrieve waste from MSSS. The waste will then be packaged for storage, reducing the risk posed, ready for final treatment and disposal. 5. This permission is associated with installation and inactive commissioning only for SEP2 and SEP1. ONR s permissioning strategy identifies a further hold point prior to use of these SEP machines to retrieve waste (i.e. prior to active commissioning) and additional engagement will be undertaken with the licensee prior to this to provide further regulatory confidence in their proposals and demonstration that the overall risk continues to be as low as reasonably practicable. Outcomes of assessment and inspection work carried out by ONR in consideration of this request 6. ONR has carried out a programme of work to provide regulatory confidence that the activities proposed by the licensee in this modification minimise risks to the public and workers so far as is reasonably practicable (SFAIRP). 7. It is acknowledged that installing the two SEP machines, each weighing ~400 tonnes, on the operations floor presents the potential for historic leak paths to re-open due to the additional stress on the building. However, this additional risk is tolerated as the SEP machines are identified as the best option for emptying the waste from the silos Office for Nuclear Regulation Page 3 of 12

4 and ONR concurs with SL that it is necessary to undertake the waste retrieval. Upon completion of waste retrieval, a major societal risk will be significantly reduced. 8. ONR has sought regulatory confidence that a catastrophic failure of the structure giving significant radiological consequences is highly unlikely. ONR civil engineering specialist inspectors have therefore undertaken a series of engagements and assessments with the licensee to consider their case regarding the ability of the building to withstand the additional loads from the SEP machines. They concluded that the SEP machines can be installed and operated without threatening existing safety margins, noting that there are a number of existing structural defects and unusual structural features in the building. The existence of existing historic leak paths, which have self-sealed, mean that it is not possible to rule out that these leak paths may reopen; however, as with previous leakage, SL s groundwater modelling shows that there would be negligible consequences to the public or workers. 9. ONR has sampled evidence to gain regulatory confidence in the licensee s arrangements for detection of a leak, including inspections of SL s ability to respond either to an underground leak or in the event of any above ground leak. No significant shortfalls were identified and ONR has a high level of confidence in SL s ability to deal with any events. ONR has also worked in partnership with the Environment Agency, the licensee and the Nuclear Decommissioning Authority, providing information to key stakeholders. 10. SL has undertaken an ongoing programme of work looking at technologies that could be deployed to prevent existing radioactive contamination spreading further; however, it has concluded that most of the contamination is not mobile and there are significant risks to the silos from technologies applied close to the ageing building. SL s strategy is to remove the hazardous waste from the silos prior to deploying additional decommissioning and remediation solutions. SL continues to monitor technologies that may be applied in the event of significant additional leakage and ONR will continue to regulate to ensure that risks from MSSS are reduced as soon as is reasonably practicable. 11. Any damage to the SEP machines during installation will result in delays to the hazard and risk reduction objective. In order to gain additional regulatory confidence, ONR carried out a targeted engagement using mechanical engineering and human factors specialist inspectors to assess heaviest and most onerous lift in the west end hoist well. This resulted in SL adopting improvements to minimise the risk of damage. Conclusions 12. To conclude, I am broadly satisfied with the claims, arguments and evidence laid down within the plant modification proposal and supporting documentation that the risks on Sellafield site are minimised by removal of the waste from MSSS as soon as practicable and that the installation of SEP2 and SEP1 minimises the risks from MSSS overall, despite the increase in risk during installation and subsequent operation of the SEP machines. Recommendation 13. This project assessment report recommends that the Agreement (LI 890) is issued to SL in regard of the application to commence installation and then inactive commissioning of Silo Emptying Plant (SEP)2 and SEP1 mobile caves in the Magnox Swarf Storage Silo (MSSS). Office for Nuclear Regulation Page 4 of 12

5 LIST OF ABBREVIATIONS ALARP HOW2 MSSS NDA NSC ONR PMP RIM SEP SFAIRP SL TAG As low as reasonably practicable (Office for Nuclear Regulation) Business Management System Magnox Swarf Storage Silo Nuclear Decommissioning Authority Nuclear Safety Committee Office for Nuclear Regulation Plant Modification Proposal Regulator Interface Meeting Silo Emptying Plant So Far As Is Reasonably Practicable Sellafield Limited Technical Assessment Guide (ONR) Office for Nuclear Regulation Page 5 of 12

6 TABLE OF CONTENTS 1 PERMISSION REQUESTED BACKGROUND ASSESSMENT AND INSPECTION WORK CARRIED OUT BY ONR IN CONSIDERATION OF THIS REQUEST MATTERS ARISING FROM ONR S WORK CONCLUSIONS RECOMMENDATIONS REFERENCES Office for Nuclear Regulation Page 6 of 12

7 1 PERMISSION REQUESTED 1. The Licensee requested ONR's agreement, via its arrangements made under Licence Condition 22(1), to commence installation followed by inactive commissioning of Silo Emptying Plant (SEP)2 and SEP1 mobile caves in the Magnox Swarf Storage Silo (MSSS). (Reference 3). 2 BACKGROUND 2. As required under its arrangements, Sellafield Limited has requested the Office for Nuclear Regulation s agreement to commence installation and then inactive commissioning of Silo Emptying Plant (SEP)2 and SEP1 mobile caves in the Magnox Swarf Storage Silo (MSSS). This activity is described in PMP Stream/ /0527 (Reference 4) and is indicated as Hold Point 1 in the MSSS Stream Activity Plan (Reference 5) and on the L3 Regulator Interface Meeting (RIM) hold point control plan. 3. The Magnox Swarf Storage Silo (MSSS) is a legacy facility that represents one of the largest nuclear hazards in the United Kingdom. The facility comprises 22 vertical concrete silos, partially below ground level, that were in active use between 1964 and 1991 to store fuel cladding arising from the decanning of Magnox fuel elements. Each compartment holds approximately 500m 3 of waste. Corrosion of the fuel cladding, or swarf, means that the ageing silo compartments contain a large inventory of radioactive waste (a mixture of intermediate level solid and liquid waste, and miscellaneous beta gamma waste). This modification relates to installation of equipment to facilitate waste retrievals from the 6 original building compartments and 6 first extension compartments only. The remaining 10 compartments in the second and third extension are not included. 4. A recent assessment carried out by ONR (Reference 6) concluded that the overall risk arising from the ageing MSSS facility is intolerable and the risk continues to increase significantly with time as the building structure ages. A significant structural failure would have major radiological consequences; therefore, retrieval of the waste is a national priority that must be dealt with promptly. 5. To minimise the overall risk, ONR s regulatory strategy has been developed to help facilitate improvements at Sellafield to encourage hazard and risk reduction whilst maintaining adequate safety standards. To achieve this, ONR is focussed on ensuring that Sellafield Ltd progresses retrievals and subsequent decommissioning as quickly as is safely possible whilst maintaining continued safe storage of the MSSS radioactive inventory. 6. Removal of the radioactive inventory will be achieved using three machines known as the Silo Emptying Plant (SEP), which will remotely and mechanically retrieve waste from MSSS. The waste will then be packaged for storage, reducing the risk posed, ready for final treatment and disposal. 7. The SEP machines operate on a rail system and remove waste via a hydraulic grab and tooling system through an import/export tunnel sited on top of the silos. Each 400 tonne machine has been subject to rigorous testing prior to being dismantled and transported to Sellafield, where they will be reassembled inside MSSS. 8. A significant amount of radioactive liquor has historically leaked from the original building silo and contaminated the land below the silo. The leakage stopped without licensee intervention but there is a risk that the proposed activities may re-open these leaks. As the facility continues to deteriorate with age, installation and use of the heavy SEP machinery has the potential to open up new or existing, below or above ground Office for Nuclear Regulation Page 7 of 12

8 leak paths within the containment structure. Even a small leak above ground has the potential to cause significant local contamination, potentially resulting in delays to retrievals. In addition, this would also impact hazard and risk reduction across other nearby plants on the Sellafield site. 9. ONR recognises that a temporary increase in risk from the current level is necessary to commence retrievals and achieve reduction in risk and hazard in the longer term. We will maintain a proportionate regulatory approach, and will seek assurance from Sellafield Ltd that the overall risk has been reduced as low as reasonably practicable. 10. The licensee has identified that the waste retrievals operations result in higher risks than installation and inactive commissioning; however, they maintain the risks are acceptable and essential in order to remove the hazard and future increasing risk from MSSS. ONR concurs with the licensee that it is necessary to take action as soon as practicable whilst accepting some increased risk for the duration of waste retrieval. If action is not taken, at some point in the future the ageing structure will inevitably deteriorate to a point where loss of containment becomes likely. 11. ONR s permissioning strategy currently identifies a further hold point prior to use of the SEP machines to retrieve waste (i.e. prior to active commissioning) and additional engagement will be undertaken with the licensee prior to this to provide further regulatory confidence in their proposals and demonstration that the overall risk continues to be as low as reasonably practicable. 3 ASSESSMENT AND INSPECTION WORK CARRIED OUT BY ONR IN CONSIDERATION OF THIS REQUEST 12. ONR has carried out a programme of work to provide regulatory confidence that the activities proposed by the licensee in the modification minimise risks to the public and workers so far as is reasonably practicable (SFAIRP), noting that it is imperative to remedy this legacy risk that increases with time. A targeted approach has been undertaken focussing on the new activities proposed for installation and inactive commissioning and the resulting risks that need to be managed by the licensee and demonstrated to be ALARP. It should be noted that many other activities are both planned and ongoing within the MSSS facility to further reduce risks, enable retrieval of the waste or maintain safe storage. This report relates risks arising from the activities proposed by the licensee in this application only. 13. The lifting of equipment onto the operations floor using the 55 tonne overhead travelling crane is covered by an existing safety case. The introduction of the SEP machines is a major change of scope and so the licensee has categorised the changes as in accordance with their procedures as Category B. SL has not identified any new credible faults as a result of installation and inactive commissioning that could result in significant radiological doses to a worker (annual dose limit) or member of the public (<1mSv). ONR s current regulatory strategy defines a proportionate approach to regulation utilising flexible permissioning arrangements agreed with the licensee. A Category B proposal would generally be a candidate for an engagement window culminating in a decision and release of a hold point. However, the additional weight on the building could potentially result in re-opening of existing historic leak paths in the original building and creation of new leak paths during the lifetime of the retrievals project cannot be ruled out. I consider a formal hold point proportionate recognising the public interest and the potential for a detrimental impact on long term hazard reduction, if the SEP machine is not installed successfully. 14. In addition, the Sellafield Nuclear Safety Committee (NSC) 119 (Reference 14) noted broad agreement with the principles in the proposal, but noting the significance it Office for Nuclear Regulation Page 8 of 12

9 requested a further submission on the broader impact of the change proposed that went to NSC 122 in September Throughout this project, ONR has carried out many engagements to inspect the design and works testing. This will continue with the next formal hold point being for active commissioning. The previous two formal engagements were; Engagement Window EW41 closed in March 2015, related to regulatory confidence in SL s readiness to commence dismantling of SEP2 following works testing programmes to demonstrate that SEP2 systems operate as designed (Reference 7); Engagement Window EW14, closed in November 2013 related to a number of inspections and engagements throughout inactive works testing and commissioning by several inspectors. (Reference 8) 16. It is acknowledged that installing the two SEP machines, each weighing ~400 tonnes, on the operations floor presents the potential for historic leak paths to re-open due to the additional stress on the building. A significant amount of civil and structural engineering assessment has been undertaken by the licensee to gain confidence that the building will successfully support the weight spread over the installed rails; however, the fact that there have been historic leaks, the age of the building and the inability to examine the below ground structure all add to the challenges facing the licensee. ONR civil engineering specialist inspectors have therefore undertaken a series of engagements and assessments with the licensee to consider their case regarding the ability of the building to withstand the additional loads from the SEP machines. 17. ONR has sampled evidence to gain regulatory confidence in the licensee s arrangements for leak detection, including inspections of SL s ability to respond either to an underground or above ground leak (noting that the licensee has considered severe leakage due to catastrophic structural failure to be beyond the design basis expected for consideration i.e. extremely unlikely). 18. As noted above, the use of the west end crane for lifting equipment up to 55 tonnes onto the operations floor level is covered by an existing safety case. However, ONR has carried out a targeted engagement using a mechanical engineering specialist inspector, supported by a human factors specialist inspector to gain additional regulatory confidence in the heaviest lift, which also has the smallest clearance gaps in the west end hoist well. It is essential for hazard and risk reduction that the waste and liquor is removed from the building as soon as reasonably practicable while the structure is sound, hence, confidence is also required in the ability of SL to undertake the lift without damaging the parts of the SEP machine as any damage will delay the hazard and risk reduction objectives of the project. It should be noted that SL has already dismantled nearly the whole of SEP2 at works at Wolverhampton, transported and stored it safely to a site local to the licensee. 19. Given the increase in risk associated with this work to gain the essential long-term hazard and risk reduction benefits, ONR has also worked in collaboration with the Environment Agency, the licensee and the Nuclear Decommissioning Authority, to provide information to key stakeholders, including to a public meeting of the West Cumbria Site Stakeholder Group on Hazard and Risk Reduction on 16 September Office for Nuclear Regulation Page 9 of 12

10 4 MATTERS ARISING FROM ONR S WORK 20. For this assessment effort has been concentrated on civil and structural engineering relating to the new loads being placed upon the silos and emergency preparedness of the licensee with additional engagement of mechanical engineering and human factors in relation to the logistics of the bounding hoist well lift. 21. ONR civil and structural engineering specialist inspectors undertook a number of engagements and assessment on key topics: SEP Seismic Isolation Bearings. Seismic Damage Assessment Structural Implications of SEP 1 and SEP 2 Installation Increase in Loading to Existing Rails and Brackets Combined Penetrations to First Extension Original Building Perimeter Drainage Silo Movement Monitoring 22. The conclusions of the assessment report and engagements are summarised in Reference 9. In particular, Reference 17 examines the safety margins in the silos structure from installation of the SEP machines. It concludes that the SEP machines can be installed and operated without threatening existing safety margins. That said it also notes, although the introduction of plant loading within the silo structures does not materially change existing section utilisation, the presence of existing defects (original silo) and unusual structural features (first extension) has been noted in the assessments. 23. The specialist inspector concluded that SL has satisfactorily addressed all but one of the civil engineering actions, however, she concludes that, from a civil engineering perspective, she supports the release of the hold point. 24. The engagement undertaken by the mechanical engineering specialist inspector supported by a human factors specialist inspector resulted in a number of suggestions to improve the lifting process in the west end hoist well, minimising the potential to damage the module and reduce conventional health and safety risks from the use of tag lines. He subsequently received an updated copy of SL s draft method statement for the lift, which included the suggested improvements. He accepted that the draft cannot be completed until the dismantling of the SEP machine at the works has been completed and as such some information such as the weight of the component remained to be confirmed. He concluded (Reference 10) that he can see no reason for ONR to withhold permission from SL to commence installation of the SEP2 machine, based on his sample assessment. 25. In July and September 2015, ONR undertook inspections (References 11 and 12) focussing on SL s indicators of a leak and its ability to detect and deal with it; both underground from existing or new leak paths and in the very unlikely event of an above ground leak or seepage through the silo wall of the original building (the silo extensions having secondary containment). These inspections covered areas including, leak detection process, emergency preparedness support documentation, training programmes, emergency equipment storage and maintenance, fire and rescue and observation of training exercise. No significant shortfalls were identified and ONR has a high level of confidence in SL s ability to deal with events. 26. A significant amount of radioactive liquor has historically leaked from the original building silo and contaminated the land below the silo. SL has undertaken an ongoing programme of work looking to technologies to determine the best approach to Office for Nuclear Regulation Page 10 of 12

11 remediate the land and protect ground-water, however, it has concluded that there are significant risks to the silos from technologies applied close to the building. As such, SL s strategy is to remove the hazardous waste from the silos prior to deploying appropriate decommissioning and remediation solutions. SL continues to monitor technologies that may be applied and has linkages with many international remediation programmes, including Fukushima, and ONR will continue to regulate to ensure that risks from MSSS are reduced as soon as is reasonably practicable. 27. I undertook a number of engagements during the implementation of SL strategy and the development of assessments and processes required to install the SEP machines safely. These engagements did not specifically examine the technical details of SL s documents and assessment, other than those detailed above, however, the engagements, involving many SL staff such as business change managers, engineers, safety and environment assessors, project managers and project engineers provided confidence in SL s due process and their ability to manage the activities described. 28. I have gained further regulatory confidence from the fact that the licensee s proposal and supporting documents have been subject to SL s due process including consideration by the NSC (Reference 14) and subjected to independent nuclear safety assessment (Reference 16). 5 CONCLUSIONS 29. This report presents the findings of ONR s assessment of SL s proposal to commence installation and then inactive commissioning of SEP2 and SEP1 mobile caves in the Magnox Swarf Storage Silo. 30. To conclude, I am broadly satisfied with the claims, arguments and evidence laid down within the PMP and supporting documents that the risks on Sellafield site are minimised by removal of the waste from MSSS as soon as practicable and that the installation of SEP2 and SEP1 minimises the risks from MSSS overall, despite the increase in risk during installation and subsequent operation of the SEP machines. 6 RECOMMENDATIONS 31. This project assessment report recommends that Agreement (LI 890) (Reference 15) is issued to SL in regard of the application to commence installation and then inactive commissioning of Silo Emptying Plant (SEP)2 and SEP1 mobile caves in the Magnox Swarf Storage Silo (MSSS). Office for Nuclear Regulation Page 11 of 12

12 7 REFERENCES 1. ONR HOW2 Guide - Purpose and Scope of Permissioning - NS-PER-GD-014 Revision 4. July Safety Assessment Principles for Nuclear Facilities Edition Revision 0. November / Condition 22(1), Schedule 2 of the Nuclear Site Licence No: 31G Sellafield (Windscale Works and Calder Works) Application for Agreement to Commence Installation and Inactive Commissioning of SEP2 and SEP1 Mobile Caves in MSSS 18 September / Plant Modification Proposal MSSS SEP2 and 1 - PMP September / MSSS Retrievals - Overarching Modification Strategy Paper SLNSC Paper 2015/ / SL - Assessment Note - Risks Presented by Legacy Facilities at Sellafield Site - - June / Sellafield Decision Record - ONR-SEL-DR Consideration of Sellafield Limited decision to dismantle SEP2 and transfer to Site / Closure of Engagement Window 14 (EW14) on the MSSS Stream Activity Plan (SAP), inactive commissioning SEP 2 Machine, 13 November / Preparation for Retrievals, Release of Hold Point 1, Summary of Civil Engineering Actions 17 August / Mechanical Specialist response - Installation of SEP2 machine into MSSS - 21 September / ONR-SEL-IR SL Project Delivery Essential Operations Inspection - MSSS Emergency Preparedness - July / ONR-SEL-IR Sellafield - Essential Operations Inspection of MSSS Emergency Preparedness for Installation of the SEP Machines - Follow Up - 10 September / Issue of Licence Instrument to Commence Installation and Inactive Commissioning of SEP2 and 1 Mobile Caves In Magnox Swarf Storage Silo, OTH/15/026/O, 18 September / Sellafield Nuclear Safety Committee - Minutes of the 119 th meeting / LI890 Agreement to Commence Installation and Inactive Commissioning of SEP2 and SEP1 Mobile Caves in MSSS / MSSS SEP2 & 1 Installation and Inactive Commissioning Position Statement PS 2986/1 2 September / AR - ONR-SEL-AR Installation of Silo Emptying Plant within MSSS Original and First Extension Facilities - 21 July Office for Nuclear Regulation Page 12 of 12