Office for Nuclear Regulation

Sellafield – Inspection ID: 52312

Executive summary

Date(s) of inspection:

  • February 2023

Aim of inspection

This reactive inspection was undertaken on 23 February 2023 to gain confidence in the adequacy of the licensee’s arrangements for Licence Condition 11 (Emergency Arrangements) particularly in response to an excursion in the Magnox Swarf Storage Silo (MSSS).

In February 2022, ONR sent an enforcement letter which required that Sellafield Limited implement reasonably practicable measures to protect the margin between silo temperatures and excursion temperatures. The temperature which would result in an excursion is not known, however, increased temperatures could lead to overpressure and damage to the silo containment resulting in the leakage and escape of radioactive material and radioactive waste. In January 2023 slippage in progress and little engineered improvement in heat management reached a point where greater regulatory attention was warranted, therefore a second enforcement letter was sent. The requirement for this intervention was specified in that letter.

Subject(s) of inspection

  • LC 11 – Emergency arrangements – rating: Green

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

ONR attended Sellafield site to conduct a reactive LC11 inspection following the issue of an enforcement letter and concerns regarding erosion of safety margins.

The inspection scope focused on Sellafield Ltd’s arrangements for managing an excursion in the MSSS facility and also included a plant walkdown of an emergency operating instruction for pressurised inerting.

The evidence sampled included fit for purpose emergency operating instructions for pressurised inerting which were exercised routinely, training records and discussions with operators and duly authorised persons (DAPs) who were found to be suitably qualified, experienced and trained in their roles in emergency response and adequate facilities and equipment to support a response. Based on this, ONR have gained confidence in the ability of Sellafield Ltd to respond to an excursion and this inspection, in line with ONR guidance, was rated Green, warranting no formal action.


On the basis of the evidence sampled at the time of the inspection, Sellafield Limited has adequately implemented its arrangements for LC11 in MSSS and ONR has gained confidence in the ability of Sellafield Ltd to respond to an excursion. Noting the ONR guidance on inspection ratings, a rating of Green (no formal action) is considered appropriate.

It is noted that an extant regulatory issue requires the implementation of the capability to supply chilled water to the Recirculating Cooling Water (RCW) system as part of managing compartment heat within MSSS which Sellafield Ltd. is addressing via the installation of an interim chiller. There is also an action in the regulatory issue that requires confirmation that the extant safety case accurately reflects all appropriate options for compartment cooling and that those claimed are appropriately tested and have proven capability. As part of this second action, the use of the RCW supply from the cooling tower is being reviewed with a view to removing the claims on it. This method of cooling is currently included in the arrangements although it is not considered ALARP to test it due to the potential for water leaks. Sellafield Ltd. remain confident that it could be used if required. The close out of these actions and this regulatory issue will be followed up as part of ongoing engagements with Sellafield Ltd. on MSSS heat management.