Office for Nuclear Regulation

Sellafield – Inspection ID: 52789

Executive summary

Date(s) of inspection

  • September 2023

Aim of inspection

The CNI attention level for ‘safety case adequacy and currency’ is Enhanced, the aim of the inspection is to gather evidence on the effectiveness, use, and understanding of SL’s new safety case production processes to support a review of the attention level.

Subject(s) of inspection

  • LC14 – Safety documentation – Rating: Green

Key findings, inspector’s opinions and reasons for judgement made

The aim of the inspection was to gather evidence on the effectiveness, use, and understanding of Sellafield Ltd’s revised nuclear safety case production processes to support a review of the attention level. It is the first of a number of planned inspections to be undertaken by Fault Studies Specialist Inspectors which adopt the following method:

1. Selection of a developing Sellafield Ltd nuclear safety case

2. Desktop walk-through of the revised process with key safety case role-holders

3. Targeting of key steps in the revised process

4. Sample checking of alignment between key steps and the safety case development trail evidenced by records accompanied by key role-holder narratives

The overall objective is to help advance RI-11251 on Sellafield Ltd to demonstrate that revised nuclear safety case production processes are being implemented appropriately. This RI has stemmed from the findings of a previous intervention ONR-SDFW-IR-21-127 which was carried out on 17-19 November 2021 (2021/88228) to target Sellafield Ltds site wide corporate arrangements for compliance with Licence Condition 14 (LC14). These findings resulted in RI-10471 being raised on Sellafield Ltd to provide a plan for improvement leading to SL issuing revised nuclear safety case production processes. RI-10471 is now closed but has driven follow-on need for Sellafield Ltd to demonstrate appropriate implementation of the revised nuclear safety case processes via RI-11251, noting further drivers have emerged:

  • ‘enhanced’ CNI attention level on Sellafield Ltd nuclear safety cases resulting from an adverse trend of assessment findings;
  • RI-8159 concerning observed shortfalls in recording/re-evaluating key safety decisions for the MSSS safety case.

For this inspection, the selected nuclear safety case concerned transfer of BUTEX liquor (HAL) from “old side” vessels to “new side” vessels at the HALES facility.
The overall claim of the nuclear safety case is that this is done in a timely manner which reduces overall ‘time-integrated’ risk ALARP by best balancing various contributory risks:

  • current risk of storing HAL in “old side” vessels (related to ongoing asset degradation);
  • transfer risk (relating to fissile solids, breakpot overflow and threat of airborne release noting degradation of the “old side” vent duct);
  • future risk of non-disposable (“vitrifiable”) HAL wastes forming in HALES

To achieve this Sellafield Ltd have selected a transfer option using existing systems with added operational safety measures which are readily-implementable under its LC22 arrangements (Category B PMP).


From my sampling of evidence I judged that Sellafield Ltd had adequately demonstrated the effectiveness and use of its revised nuclear safety case production process in this case and therefore an inspection rating of Green (no formal action) is merited.