Executive summary
Date(s) of inspection:
- January 2025
Aim of inspection
System Based Inspections (SBIs) are an essential element of ONR’s overall intervention on a nuclear site. The Residual Heat Removal System (RHRS) is a key system during plant shut down operations to remove the decay heat from the core and reduce the temperature of the reactor coolant. It also serves as part of the emergency core cooling system for a loss of coolant accident (LOCA).
The aim of this inspection at the EDF-NGL Sizewell B site was to:
- determine whether the Structures, Systems and Components (SSCs) associated with the RHRS and associated support systems can adequately fulfil their safety duties (safety functional requirements), in line with claims made within the safety case; and
- consider the adequacy of implementation of the licensee’s spares management arrangements.
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
This SBI comprised discussions with EDF staff, review of records, and observations on plant. During the System Plant Walk-down, we identified a minor shortfall relating to the frequency of walkdown and have raised a Level 4 Regulatory Issue to resolve this.
LC10 Training
We sampled the specific training records of individuals involved in the maintenance of the RHRS who had signed off on previously examined (LC28) Work Order Cards.
We also sampled the appointment of a new RHRS Systems Engineer and identified a minor shortfall in relation to the arrangements for the appointment of Systems Engineers and have raised a Level 4 Regulatory Issue to resolve it.
LC23 Operating Rules
We sampled the Technical Specifications and Safety Case documents applicable to the RHRS to confirm that they detailed the safety basis, LCO, performance requirements and applicability to the Mode of operation specified.
LC24 Operating Instructions
We sampled several Site Operating & Plant Operating Instructions to ensure that the appropriate Technical Specifications were implemented during a particular Mode and that requirements were clearly identified throughout the documents. The instructions clearly described how tasks should be carried out and contained the necessary prerequisites, checks, precautions and actions to be taken in the interest of safety.
LC27 - Safety Mechanisms, Devices & Circuits (SMDCs)
We sampled the surveillance undertaken to ensure Technical Specification compliance and in accordance to that specified to the station Mode of operation, and any change of Mode would not take place until the applicable checklist is completed. This ensured that operations that may affect safety are tested, connected and in good working order.
LC28 Examination, inspection, maintenance and testing (EIMT)
We sampled a number of maintenance activity Work Order Cards of key RHRS items which included valves, pumps and test work. I identified a minor shortfall in relation to Written Scheme of Work arrangements and have raised a Level 4 Regulatory Issue to resolve it.
Conclusion
Overall, based on the sample of evidence and plant walkdown, some minor areas for improvement were identified but these did not impact the safety functions of the system. Therefore, we consider an overall inspection rating of Green (No Formal Action) for this System to be appropriate.