Office for Nuclear Regulation

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

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) Solid Waste Export Facility (SWEF).

Interventions Carried Out by ONR

Between 07 - 08 December 2016, ONR carried out a planned two day inspection of the THORP SWEF safety systems utilising specialists from the following technical disciplines:

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 SL's arrangements for six pre-defined licence conditions (LCs), as listed 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.

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 against the following LCs using the applicable ONR inspection guidance:

Explanation of Judgement if Safety System Not Judged to be Adequate

N/A - this system is judged to be adequate.  However, there are specific improvements that SL should make as described in the next section.

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

Whilst some minor opportunities for improvements to SL's compliance against LCs 10, 24, 27, 28 and 34 were identified in this inspection, it is my view that these licence conditions are all adequately implemented with regards to the SWEF safety related equipment and key processes. Consequently, it is my opinion that a rating of GREEN (no formal action) is appropriate for these five licence conditions.

However, with regard to LC23 (operating rules), based on the sampling undertaken, I have awarded a rating of AMBER (seek improvement). This is due to a number of issues including:

Two incidences were observed where SL's operating procedures do not fully implement safety case-derived operating instructions (i.e. limits and conditions necessary in the interests of safety).

A lack of adequate auditable close-out of identified Long Term Periodic Review improvements.

THORP's use of supplementary clearance certificates, as these do not at present provide suitable visibility to SL staff in regard to managing the plant configuration.

Despite these shortfalls, I do not recommend that the safety case supporting this system be subjected to an ONR safety case assessment earlier than would otherwise be planned.  This is in part because the safety case is about to be reviewed as part of SL's Event Driven Review process (in preparation for THORP's operations following the cessation of fuel reprocessing) and ONR intends to perform detailed assessments of the safety case at that time.

Conclusion of Intervention

I have identified three areas of shortfall in regard to the implementation of the THORP SWEF safety case and its visibility.  As such I have awarded an Amber rating (seek improvement) against LC23 (Operating Rules). Overall however, I am content that SWEF, once wider activities undertaken by SL are taken into account, adequately implements the requirements of the supporting safety case.  

Two extant regulatory issues from a previous THORP inspection (which focussed on shield doors and so is closely related to the present system based inspection) already capture ONR's issues with regards to supplementary clearance certificates and improvement close out.  These have been expanded to include the similar issues found here at SWEF.  Additionally I have raised a new Regulatory Issue as a result of this inspection with regard to the implementation of operating rule requirements into supporting procedures.