Office for Nuclear Regulation

Sellafield – Inspection ID: 52606

Date(s) of inspection:

  • December 2023

Executive summary

Aim of inspection

To determine whether the safety systems, structures and components associated with the cooling system in the Magnox Swarf Storage Silo (MSSS) are able to adequately fulfil their safety duties (safety functional requirements), in line with claims made within the safety case.

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
  • Overall Inspection Rating – Rating: Green

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

ONR carried out a planned two-day system based inspection (SBI) of the MSSS cooling system  on the 4 and 5 December, 2023. The inspection team comprised the Site Inspector for MSSS and Electrical and Chemical Engineering Specialist Inspectors.  The inspection included discussions with Sellafield Ltd. personnel, review of records, documents and processes and a targeted walk down of the facility.

MSSS arrangements and compliance against the following LCs were inspected as part of the SBI:
LC 10 – Training;
Given that the evidence confirmed that the training was sufficient to allow effective operation of the MSSS cooling system, it was considered that the arrangements for this licence condition have been implemented adequately resulting in a green inspection rating (No Formal Action).

LC 23 – Operating Rules;
The evidence sampled confirmed that the required Operating Instructions (rOIs) are available, clearly identify safety case requirements and are understood by operators resulting in a green inspection rating for this licence condition.

LC 24 – Operating Instructions;
It was judged that the operator instructions sampled included the instructions necessary to ensure that rOIs are implemented confirming that  the  arrangements for this licence condition have been implemented adequately.

LC 27 – Safety Mechanisms, Devices and Circuits;
From the sample of the licensee’s arrangements and substantiating documentation, the Licence Condition was rated green as it was judged that that suitable and sufficient safety mechanisms, devices and circuits are properly connected and in good working order.

LC 28 – Examination, Inspection, Maintenance and Testing;
Adequate examination, maintenance, inspection, and testing had been carried out based  on the documentation examined, discussions and the plant walkdown undertaken resulting in a green inspection rating for this licence condition.

LC34 – Leakage and Escape of Radioactive Materials and Radioactive Waste;
Confidence was gained in the controls in place to prevent leakage and escape of radioactive materials resulting in a green rating for this licence condition.

From the evidence sampled, it was judged that the MSSS cooling system adequately meets the requirements specified within the safety case and evidence was gained that the facility understands the limits and conditions and their importance in the safety case.


Overall, LCs 10, 23, 24, 27, 28 and 34 were found to be adequately implemented in relation to the systems inspected.

Consequently, this system-based inspection has been rated GREEN – No formal action for LCs 10, 23, 24, 27, 28 and 34.  The cooling system within MSSS is judged to be adequate.