Office for Nuclear Regulation

Sellafield – Inspection ID: 52153

Executive summary

Date(s) of inspection

  • September 2023

Aim of inspection

To determine whether the safety systems, structures and components associated with the Sellafield THORP Ventilation are able to adequately fulfil their safety duties (safety functional requirements), in line with claims made within the safety case. 

In addition to the below TIGs, the TAG on ventilation systems is also considered applicable to this inspection (NS-TAST-GD-022).

ONR will use the current version of the following TIGs:

  • NS-TAST-GD-027,  Training and Assuring Personnel Competence
  • NS-INSP-GD-023, LC23 Operating Rules
  • NS-INSP-GD-024, LC24 Operating Instructions
  • NS-INSP-GD-027, LC 27 Safety Mechanisms, Devices, and Circuits
  • NS-INSP-GD-028, LC 28 Examination, Inspection, Maintenance and Testing (EIMT)
  • NS-INSP-GD-034, LC 34 Leakage and Escape of Radioactive Materials and Radioactive Waste

Subject(s) of inspection

  • LC10 – Training – Rating: Green
  • LC23 – Operating rules – Rating: Green
  • LC24 – Operating instructions – Rating: Green
  • LC27 – Safety mechanisms, devices and circuits – Rating: Green
  • LC28 – Examination, inspection, maintenance and testing – Rating: Green
  • LC34 – Leakage and escape of radioactive material and radioactive waste – Rating: Green

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

I, the Site Inspector for Thermal Oxide Reprocessing Plant (THORP), undertook a system based inspection (SBI) of the Ventilation System at the THORP operating unit at the Sellafield Site in Cumbria. The purpose of this inspection was for ONR to determine the adequacy of implementation of Sellafield Ltd.’s safety case claims for the THORP ventilation systems. The inspection sampled the ventilation systems, filter change systems, filter caves and the associated safety measures. I assessed compliance in THORP against the following LCs by using the current versions of the applicable ONR inspection guidance documents:

  • LC 10 – Training (NS-TAST-GD-027)
  • LC 23 – Operating Rules (NS-INSP-GD-023)
  • LC 24 – Operating Instructions (NS-INSP-GD-024)
  • LC 27 – Safety Mechanisms, Devices and Circuits (NS-INSP-GD-027)
  • LC 28 – Examination, Inspection, Maintenance and Testing (NS-INSP-GD-028)
  • LC34 – Leakage and Escape of Radioactive Material and Radioactive Waste (NS-INSP-GD-034)

During the course of the inspection I found that these LCs were adequately implemented in relation to the systems inspected. One minor anomaly was identified, and I have raised a Level 4 Regulatory Issue (RI) against THORP’s system health report arrangements. Whilst some minor opportunities for improvement were identified, overall, I was satisfied with THORP’s implementation of the Sellafield Ltd arrangements, and have awarded a Green (no formal action) rating.


I was satisfied that THORP’s safety case has adequately been implemented for the THORP ventilation system and meets ONR’s expectations for the licence conditions above. There was one minor anomalies that I observed:

  • I found that the THORP system health reports that I sampled did not fully meet expectations as outlined in Sellafield Limited’s arrangements, as they were not signed-off and were completed late.  In addition, THORP’s arrangements for prioritisation of importance of the systems analysed in the health reports was no adequate. I have raise a Level 4 Regulatory Issue (RI-11739) to address the gap and to track Sellafield Limited’s plan to close the gap against RGP.

I consider an inspection rating of Green (no formal action) to be proportionate and appropriate. The Head of Operations accepted my findings and observations at the concluding meeting.