Office for Nuclear Regulation

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System Based Inspection (SBI) of the ventilation system in the Waste Vitrification Plant (WVP)

Executive summary

Purpose of intervention

The Office for Nuclear Regulation (ONR) undertakes all regulatory interaction with the Sellafield site licensee (Sellafield Limited, SL) against a strategy defined by the ONR Sellafield Programme.  In accordance with that Strategy, this system based inspection of the Waste Vitrification Plant (WVP) ventilation system was carried out in June 2015 as planned.  

The purpose of this inspection was to enable ONR consider the adequacy of implementation of the licensee’s safety case claims in respect of the ventilation system.  This system was selected because of its importance in preventing off-site contamination in the event of an accident at the plant.

As part of our system based inspections, we examine evidence of the adequate implementation of six licence conditions.  These licence conditions (listed below) have been selected in view of their importance to nuclear safety and are defined within ONR’s formal process for system based inspection.

Interventions Carried Out by ONR

I carried out a two-day, on-site, system based inspection of the WVP ventilation system utilising technical support from Mechanical Engineering (ME), Control and Instrumentation (C&I) and Human Factors (HF) specialists.  The intervention included discussions with SL staff, a plant walk down and examination of plant records and other documentation. Compliance against the following licence conditions was examined.

LC10 requires SL to make and implement adequate arrangements for suitable training of those who have responsibility for any operations that may affect safety.

LC23 requires SL to produce adequate safety cases to demonstrate the safety of its operations, to identify operating conditions and limits necessary in the interests of safety and to ensure its operations are at all times carried out in compliance with these conditions and limits.

LC24 requires SL to make and implement adequate arrangements for the provision of suitable written instructions for undertaking any operation that may affect safety.

LC27 requires SL to ensure that, before a system is operated, inspected, maintained or tested, all safety mechanisms, devices and circuits are properly connected and in good working order.

LC28 requires SL to make and implement adequate arrangements for the regular and systematic examination, inspection, maintenance and testing of all plant which may affect safety.

LC34 requires SL to ensure that its radioactive material and radioactive waste is at all times adequately controlled and contained, and that no leak or escape of that material or waste can take place without being detected.

Explanation of Judgement if Safety System Not Judged to be Adequate

It is my opinion that the ventilation system on the plant is not an adequate implementation of the safety case. The training of key personnel has not suitably embedded in them an appropriate understanding of the operating limits and conditions necessary in the interests of safety. Furthermore, the key engineered protective systems are not to an appropriate industry standard and the identified substantiation shortfalls have not been managed effectively. Notwithstanding this, it is my opinion that the relevant operational risks are adequately mitigated by the extant ventilation arrangements and, consequently, operations could continue. The commitment given by SL to urgently address the identified concerns further supports my decision.

Key Findings, Inspector's Opinions and Reasons for Judgements Made

It is my opinion that SL has not adequately identified and implemented through training and supporting documentation, instructions, procedures etc. the requirements necessary to deliver key safety case claims. In particular, key operational personnel did not show an appropriate understanding of operating limits and conditions to enable them to comply with an operating rule, identify ventilation problems, diagnose the cause(s) and undertake an appropriate targeted response. Consequently, it is my opinion that these findings highlight a lack of integration between training, identification of operating rules and production of suitable operating instructions and so an IIS rating of below standard (4) is appropriate for compliance against LCs 10, 23 and 24. I have raised a Regulatory Issue to track SL’s progress in addressing these concerns.

I believe that SL has not addressed the shortfalls it had identified against appropriate industry standards on key engineered protective safety systems and was therefore not able to demonstrate the substantiated capability of these safety mechanisms to deliver the safety functions specified in the safety case. The engineered systems presently in place do provide significant protection, albeit at a lower confidence level, while further mitigation is provided by other safety systems not formally claimed in the safety case. The current situation is considered to be below standard and it is my opinion that an IIS rating of below standard (4) is appropriate for compliance against LC 27. I have raised a Regulatory Issue to track SL’s progress in addressing these shortfalls.

I identified a number of areas of good practice within this inspection, notably within the arrangements for the management of software control, the    simple, clear and well-designed surveillance and operator checks and the knowledge of the Duly Authorised Persons. With regard to the system’s physical condition, I welcome the work SL is doing to improve its understanding of the health of the ventilation system. 

SL demonstrated good control and delivery of maintenance and plant inspection.  There was also some evidence that SL has started to develop a proactive approach to asset care for this system. Nevertheless, I consider that SL still has work to undertake before it has a full understanding of asset condition within the ventilation system.   However, I note the planned and funded programme of improvements which gives me confidence that this will be achieved in a timely manner. Consequently, it is my opinion that an IIS rating of adequate (3) is appropriate for compliance against LCs 28 and 34.

Conclusion of Intervention

From the evidence sampled during this inspection, I judge that the licensee has not adequately implemented key aspects of the safety case. Notwithstanding this, it is my opinion that the relevant operational risks are adequately mitigated by the extant ventilation arrangements. It is also evident that the facility would react conservatively in response to an event and place the plant in a safe state. Furthermore, SL had given a commitment to urgently address the identified shortfalls. Consequently, it is my opinion that operations could continue.

It is my opinion that the extant safety case, with respect to ventilation, does not warrant a review as the safety arguments and resultant designations are deemed appropriate.

As identified above, I have raised ONR Regulatory Issues to track SL’s progress in addressing the identified concerns.