Office for Nuclear Regulation

Transcription

1 Office for Nuclear Regulation Waste Vitrification Plant (WVP), Line 3 Gamma Monitor Replacement Agreement to Proceed with Modification to an existing plant, WVP Line 3 Shield Doors 6 th June 2013

2 Crown copyright 2012 You may reuse this information (excluding logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view the licence visit write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or Some images and illustrations may not be owned by the Crown so cannot be reproduced without permission of the copyright owner. Enquiries should be sent to Unless otherwise stated, all corporate names, logos, and Registered and Trademark products mentioned in this Web site belong to one or more of the respective Companies or their respective licensors. They may not be used or reproduced in any manner without the prior written agreement of the owner(s). For published documents, the electronic copy on the ONR website remains the most current publically available version and copying or printing renders this document uncontrolled. Page 1

3 EXECUTIVE SUMMARY Title Sellafield (Windscale and Calder Works) - Agreement to Proceed with Modification to an Existing Plant, Waste Vitrification Plant (WVP) Line 3 Shield Doors Permission Requested Sellafield Ltd. has requested an Agreement to proceed with a modification to an existing plant. The safety documentation relates to the shield door recovery project on the Waste Vitrification Plant (WVP) Line 3, specifically the implementation of 7 gamma monitors replacements which will improve reliability of these important safety measures. The request is related to the Office for Nuclear Regulation s (ONR) previous Acknowledgment of the Overarching Strategy Paper (OSP) for the Implementation of Phases 1 & 2 Permanent modifications to the WVP Line 3 Shield and Trap Doors. As a result of its review of the OSP the replacement of the 7 gamma monitors was identified as a hold point by ONR. Background Line 3 has two hydraulic ring main systems which drive a number of shield and trap doors. On the 18 th September 2008, two trap doors and a number of hydraulic locks moved unexpectedly on WVP Line 3. Although there were no consequences to personnel, nuclear safety barriers were compromised. The subsequent review led to the need to improve the protection associated with the shield and trap doors within WVP Line 3 and Sellafield Ltd. adopted a phased approach in implementing the improvements. Phase 1 introduced a number of engineering modifications to protect against inadvertent operation of the shield and trap doors and reduced the reliance on administrative controls. The aim of Phase 2 is to provide an engineered mechanism to lock the shield doors and to revise the shield doors safety case. Once completed, it will mark the end of the shield door recovery project. This latest submission provides details of the implementation of the 7 gamma monitor replacements on WVP Line 3 shield / trap doors, which will be undertaken during Phase 2. Assessment and inspection work carried out by ONR in consideration of this request In support of this Agreement, ONR has reviewed the submission and carried out an inspection related to the readiness of plant to implement these modifications. Matters arising from ONR s work From the review of the submitted documentation, ONR believes the approach proposed is appropriate. It is ONR s opinion that the submission is of good quality and has built on the experience gained from Phase 1 works, providing further confidence in the adopted approach and the readiness inspection reinforced this point. Conclusions From the review of the documentation submitted by Sellafield Ltd. and the readiness inspections, ONR has no objections to this work, which will result in both engineered and procedural improvements for shield / trap door operations, this enhancing safety on plant. Recommendation It is recommended that Licence Instrument (LI) 859 be issued, agreeing to the request to proceed with the modification to an existing plant, related to the implementation of 7 gamma monitor replacements on WVP Line 3 shield / trap doors. Page 2

4 Page 3

5 LIST OF ABBREVIATIONS CNS HLWP HAL HSE LI OA ONR OSM OSP PAR PMP roi WVP Civil Nuclear Security (ONR) High Level Waste Plant Highly Active Liquor The Health and Safety Executive Licence Instrument Operating Assumption Office for Nuclear Regulation (an agency of HSE) Operational Safety Memorandum Overarching Strategy Paper Project Assessment Report Plant Modification Proposal Required Operating Instruction Waste Vitrification Plant Page 4

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 Page 5

7 1 PERMISSION REQUESTED 1 The licensee requested ONR s Agreement to proceed under Licence Condition 22 with a modification to existing plant, this Project Assessment Report (PAR) has been written to support a recommendation to issue a Licence Instrument (LI) (Ref 1), for Agreement to proceed with the modification, specifically 7 off Channel 2 AGM-3 gamma monitor replacement (Ref 2) on the Waste Vitrification Plant (WVP) Line 3 shield and trap doors. The modification forms part of the WVP Line 3 Shield Door Recovery Project (Ref 3). Sellafield Ltd. s submission describes the safety case related to the installation period and also the effect on the permanent safety case, as set out in Sellafield Ltd. s application letter (Ref 4). 2 BACKGROUND 2 Located within the High Level Waste Plants (HLWP) complex, WVP incorporates Highly Active Liquor (HAL) into a solid glass matrix, which is then sealed within stainless steel containers producing a waste that is suitable for safe, long-term storage. Shield and trap doors protect operators against either access to, or radiation shine, from cells containing WVP product containers, vitrified waste or HAL bearing liquors. The shield and trap door control system is therefore designed to be a high integrity interlocked system because faults have significant potential nuclear and radiological safety impact on the workforce. Consequently these systems are designated as Safety Mechanisms. 3 Line 3 has two hydraulic ring main systems which drive a number of shield and trap doors. On the 18 th September 2008, two trap doors and a number of hydraulic locks moved unexpectedly on WVP Line 3. Although there were no consequences to personnel, nuclear safety barriers were compromised. The subsequent review led to the need to improve the protection associated with the shield and trap doors within WVP Line 3 through the shield door recovery project. 4 The shield door recovery project is being implemented progressively, as stated in the Overarching Strategy Paper (OSP) acknowledged in February 2009 (Ref 3). Phase 1 of the project introduced a number of engineering modifications to protect against inadvertent operation of the shield and trap doors and reduced the reliance on administrative controls. Phase 1 works are now complete. The aim of Phase 2 is to provide an engineered mechanism to lock the shield doors and to revise the shield doors safety case. Once completed, it will mark the end of the shield door recovery project. 5 WVP Line 3 uses gamma monitors for radiological protection. These monitors are of importance in providing protection against high consequence events associated with operation of the shield doors. The monitors therefore form an integral part of the shield door interlocks. On 8 th March 2009 a WVP Line 3 AGM-3 gamma monitor failed in a potentially unsafe manner. The failure mode related to parameter data corruption and the ability of the digital and analogue measurements to read differing and incorrect values, which invalidated the trip setting. 6 Sellafield Ltd. recognised that substantiation of these gamma monitors would not be achieved and hence proposed to replace them. These modifications did not originate from the shield door recovery project, but emerged as a result of an event related to the reliability of the monitors. However, Sellafield Ltd. decided to include within the shield door recovery project, the replacement of those AGM-3 gamma monitors related to preventing access to cells if the dose rate is over 500 µsv/hr Sellafield Ltd. have already replaced the AGM-3 gamma monitors in one of the interlock channels for each cell with a G64 gamma monitor which is substantiated to SIL (Safety Page 6

8 Integrity Level) 1 requirements and this was undertaken during Phase 1 of the Shield Door Recovery Project. Sellafield Ltd. are proposing to replace the second channel with a Lab Impex gamma monitor substantiated to SIL 2 and this modification forms part of the Phase 2 works of the Shield Door Recovery Project. 8 The Operational Safety Memorandum (OSM) and Plant Modification Proposal (PMP) (Ref 2) for the gamma monitor replacement (channel 2) has now been received and this PAR supports a recommendation to agree to the modifications proceeding. 3 ASSESSMENT AND INSPECTION WORK CARRIED OUT BY ONR IN CONSIDERATION OF THIS REQUEST 9 The OSM and PMP were prepared in accordance with Sellafield Ltd. s arrangements and provide the details related to Sellafield Ltd. s case for the installation phase of the gamma monitor replacement (channel 2) and also the effect on the permanent safety case, which was approved by the WVP Management Safety Committee (Ref 5). 10 Due to the reliability issues associated with the existing AGM-3 monitors, additional enhanced administrative controls and health physics checks are required prior to / and during operation of a shield door. The proposed modification offers an improvement to nuclear safety from the current arrangements (engineering improvement and reduction in administrative controls). However, it should be noted that although the modifications outlined in the OSM will result in engineered and procedural improvements for shield / trap door operations, administrative controls are required to implement the replacement gamma monitors and the control of these over the period of implementation. 11 ONR believes the OSM and PMP adequately describes the proposal for replacement of the gamma monitors and the measures for safety, which is in line with and builds on the experience gained during the channel 1 gamma monitor replacement works, which ONR approved in November (Ref 6). As the AGM-3 monitors are to be replaced ONR s Control, Electrical & Instrumentation specialist has been involved with this permissioning activity. 12 The submission centres on the installation of these monitors and identifies the main hazards as Shine paths through the penetration created by removal of the detector Spurious opening of the shield doors Attempted operation of the shield doors during the modification work 13 These hazards have been addressed within the extant Phase 1 Operations OSM. Previous ONR assessment (Ref 3) of the safety case has shown the proposed safety measures to be suitable for their intended function. 14 The latest submission identifies an additional temporary roi (required operating instruction) to ensure Phase 2 modifications or intrusive maintenance of the hydraulic system do not take place in a cell at the same time as the replacement of the AGM-3 gamma monitors. The submission also identifies an additional temporary OA (operating assumption) to carry out end to end proof testing of all the gamma monitors following installation to ensure they function correctly. These additional safety measures provide further protection against the hazards associated with replacing the AGM3-3 gamma monitors. 15 A readiness inspection was carried out for this request for Agreement to replace 7 AGM-3 gamma monitors (Ref 7). During the inspection the following areas were examined: Page 7

9 Training Operator Instructions Commissioning Examination, Inspection, Maintenance & Testing Management Arrangements Implementation Arrangements / controls Configuration Control Emergency Arrangements 16 During the inspection ONR found that the Method Statement and the Commissioning Document that will be used during the modification were awaiting final Sellafield Ltd. approval. ONR stated that these documents will need to be approved prior to permissioning. ONR s Control, Electrical & Instrumentation specialist sampled Sellafield Ltd. s documented arrangements covering installation and test of the new equipment and these were found to be appropriate. In addition ONR found that the teams involved with the installation and proof testing of the gamma monitors were awaiting specific training to undertake the modification. ONR requested Sellafield Ltd. to provide details of the training schedule for these teams to undertake the modifications. Sellafield Ltd. has provided confirmation that the documents have been approved along with schedule of training (Ref 8) and they are deemed adequate. 17 Given the number of administrative controls required to implement the replacement gamma monitors, ONR was encouraged that Sellafield Ltd. had engaged with Human Factor Specialists to ensure their procedures to undertake the modifications were suitable. 18 Overall, the outcome of the readiness inspection was satisfactory and ONR found many examples of how the implementation arrangements reinforced the safety case. ONR was also encouraged that Sellafield Ltd. was learning and building on the lessons learned from Phase I works. 4 MATTERS ARISING FROM ONR S WORK 19 From a review of the submitted documentation, ONR believes that the approach proposed is appropriate. It is ONR s opinion that the submission (encompassed by the OSM and PMP) is of good quality and has built on the experience gained from Phase 1 works, providing further confidence in the adopted approach and the readiness inspection reinforced this. 20 The Environment Agency (Ref 9) and ONR s Civil Nuclear Security (CNS) (Ref 10) have stated that they have no objection to the issue of an LI. 5 CONCLUSIONS The approach outlined within the OSM and PMP is an appropriate strategy for the replacement of the AGM-3 gamma monitors. The proposed safety measures for the modifications and period of implementation are suitable for their intended function and will ensure continual safety. Page 8

10 Inspection has confirmed the arrangements stated in the safety case are adequate and the plant is ready for implementation of the replacement gamma monitors. ONR is encouraged the modification will result in both engineered and procedural improvements for shield / trap door operations, which is proportionate to the hazard, in-line with accepted good practice, and will serve to improve the level of protection on the plant. The OSM has been discussed with the Environment Agency (Ref 9) and ONR s CNS (Ref 10) and they have stated they have no objection to the issue of an LI. 21 To conclude, ONR is satisfied with the claims, arguments and evidence laid down within the OSM and PMP which will result in engineered and procedural improvements for shield / trap door operations, further enhancing safety. This together with the experience gained from the Phase 1 works gives confidence that the approach recommended is appropriate. 6 RECOMMENDATIONS 22 The project assessment report recommends that Licence Instrument No 859 be issued, agreeing to the request to proceed with the modification to an existing plant, related to the implementation of 7 gamma monitor replacements on WVP Line 3 shield / trap doors. Page 9

11 7 REFERENCES 1 Agreement to proceed with a modification to an existing plant, WVP Line 3, Licence Instrument 859, (TRIM 2013/200332) 2 PMP WVP/B868/0792, Replacement of the 7 off Channel 2 AGM-3 Shield and Trap Door Gamma Monitors with Lab Impex Monitors, Modifications form part the Phase 2 of the WVP Line 3 Shield Door Recovery Project. Implementation of Operational Safety Memorandum Cult: B868/OSM/14895, (TRIM 2012/386108) 3 Acknowledgement of receipt of Safety Documentation (OSP) for modification to an existing plant, WVP Line 3 Shield Door Recovery Project Phase 1 & 2, Licence Instrument 774, (TRIM 2010/202545) 4 Letter from Sellafield Ltd. requesting Agreement to Proceed, NII/08/9020/26 dated 3 rd October 2012, (TRIM 2012/386108) 5 WVP MSC Committee Minutes of Meeting 99, Friday 10 th August (TRIM 2012/411381) 6 Agreement to proceed with a modification to an existing plant, WVP Line 3 Shield Door Recovery Project, Implementation of 7 off AGM-3 Gamma Monitor Replacements (Channel 1) Licence Instrument 787, (TRIM 2010/441793) 7 ONR Intervention Report, Readiness Inspection for WVP Line 3 Channe1 2 Gamma Monitor Replacement (TRIM 2013/169968) 8 from Sellafield Ltd. regarding approval of documents and details of training schedule for PMP (TRIM 2013/187999) 9 from Environment Agency regarding any objections to LI (TRIM 2013/199469) 10 from CNS regarding any objections to LI (TRIM 2013/199473) Page 10

12 Page 11