Office for Nuclear Regulation

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The Thermal Oxide Reprocessing Plant (THORP) on Sellafield Ltd.'s nuclear licensed site at Sellafield, Cumbria

Executive summary

Purpose of intervention

In accordance with the Office for Nuclear Regulation's (ONR's) Sellafield Strategy, each year ONR performs a series of planned system based inspections (SBIs) targeted at key safety significant systems on those facilities with the potential to give rise to offsite effects to the public. The purpose of this inspection was for ONR to determine the adequacy of implementation of Sellafield Ltd.'s (SL's) safety case claims in respect of the Thermal Oxide Reprocessing Plant's (THORP's) nuclear fire safety system.

Interventions Carried Out by ONR

Between 28 - 29 June 2016, ONR carried out a planned 2 day inspection of the THORP nuclear fire safety system utilising specialists from the following technical disciplines:

Site Inspection

In order to determine the adequacy of implementation of the licensee's safety case claims in respect of this system ONR examined evidence regarding the implementation of Sellafield Ltd.'s arrangements regarding the five pre-defined licence conditions(LCs) listed at 1.5 below. These LCs have been selected in view of their importance to nuclear safety and are defined within ONR's formal process for system based inspection. Whilst LC 34, leakage and escape of radioactive material and radioactive waste, is normally included for assessment as part of system based inspections, I judged that it was not applicable to this inspection due to the nature of the system under inspection and hence has not been considered further in this report.

The inspection involved reviewing the applicable safety case claims and sampling, through a combination of document reviews, discussions with operators and plant inspections, suitable evidence to determine compliance against these LCs on the plant.

ONR assessed compliance in THORP with the following Licence Conditions (LCs) using the applicable ONR inspection guidance:

Explanation of Judgement if Safety System Not Judged to be Adequate

It is my opinion, based on the sampling undertaken, that SL has not been able to adequately demonstrate that the THORP nuclear fire system has been adequately implemented in accordance with the safety case requirements. This was my opinion principally because at the time of the inspection Sellafield Ltd had not completed the ongoing process of implementing the nuclear fire safety case in THORP.

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

My inspection of on-plant passive fire protection measures found them to be in good condition and well maintained. Furthermore, I found that day to day operational control of nuclear fire safety and any associated defects appeared robust thereby demonstrating good situational awareness.

The progress of implementation of the THORP nuclear fire safety case has, however, fallen short of both Sellafield Ltd's and ONR's expectations. I was, however, encouraged by Sellafield Ltd.'s recognition of my concerns and its development of what appeared to be comprehensive and credible recovery plan.

Whilst some opportunities for minor improvements to Sellafield Ltd.'s compliance against LCs 10, 24 and 28 were identified, it is my view that these licence conditions are all adequately implemented with regards the nuclear fire safety system. Consequently, it is my opinion that a rating of GREEN (No formal action) is appropriate for these licence conditions.

With regard to LC23 (operating rules), based on the sampling undertaken, I have awarded a rating of AMBER (seek improvement). This is because, in my opinion, the safety case is not suitably visible, user friendly or available. Furthermore, key implementation documents (fire barrier drawings etc.) are not yet in an approved status and as such represent specific significant weaknesses in the implementation of the safety case when assessed against ONR's inspection guidance.

With regard to LC27 (safety mechanisms and devices) based on the sampling undertaken I have awarded a rating of AMBER (Seek improvement). This being due to specific significant weaknesses in implementation of the safety case, principally that currently SL has not appropriately designated all nuclear fire detection/protection systems important to nuclear fire safety.

Conclusion of Intervention

I judge, based on the sampling undertaken, that the nuclear fire safety systems do not adequately fulfil the THORP safety case requirements. I am, however, suitably content that these shortfalls are such that they do not represent a significant nuclear safety risk which requires immediate action. This is my opinion because of the generally robust standards of operational nuclear fire safety and high nuclear fire safety standards of passive protection measures observed on plant.

I have identified a number of areas where further work is required to return Sellafield Ltd to full compliance. As such I have raised a Regulatory Issue to record ONR's expectation that SL will urgently fully identify and address the shortfalls relating to the implementation of the THORP nuclear fire safety case. The Regulatory Issue will also provide regulatory oversight and visibility of SL's progress against ONR's expectations.