Executive summary
Date(s) of inspection: April 2024
Aim of inspection
This was a planned inspection of the implementation of EDF Nuclear Generation Limited's (NGLs) safety case claims relevant to the high extreme ambient temperature (HEAT) hazard at Heysham 1 (HYA) and Heysham 2 (HYB) Power Stations, and that associated risks are reduced as low as reasonably practicable (ALARP). This record pertains to HYA.
The inspection is one of several activities undertaken by ONR relevant to HEATs and the associated regulatory issue (RI). The RI was raised following the July 2022 elevated temperature event that revealed gaps in relevant safety cases, associated operational arrangements and plant performance. EDF NGL has been implementing enhancements to address these gaps.
The inspection is one of several activities undertaken by ONR relevant to HEATs and the associated regulatory issue (RI). The RI was raised following the July 2022 elevated temperature event that revealed gaps in relevant safety cases, associated operational arrangements and plant performance. EDF NGL has been implementing enhancements to address these gaps.
The inspection has assessed the adequacy of EDF NGL’s implementation of arrangements for managing risks from HEATs by reviewing compliance against the following licence conditions (LCs):
LC22 - Modification or experiment on existing plant.
LC23 - Operating rules.
LC24 - Operating instructions.
LC28 - Examination, inspection, maintenance and testing.
LC22 - Modification or experiment on existing plant.
LC23 - Operating rules.
LC24 - Operating instructions.
LC28 - Examination, inspection, maintenance and testing.
Subject(s) of inspection
- LC22 - Modification or experiment on existing plant - Rating: Green
- LC23 - Operating rules - Rating: Green
- LC24 - Operating instructions - Rating: Green
- LC28 - Examination, inspection, maintenance and testing - Rating: Not rated
- Overall Inspection Rating - Rating: Green
Key findings, inspector's opinions and reasons for judgement made
We inspected updated operational arrangements to ensure risks from HEATs are being appropriately managed. Planned plant improvements were inspected to gain confidence that the systems will deliver required safety functions during a HEAT event. Our sample was informed by HYA’s HEAT Justification for Continued Operation (JCO) and included reviewing modification documentation for susceptible systems, and discussions with the system engineers.
Only those LCs for which sufficient evidence was gathered have been rated:
Only those LCs for which sufficient evidence was gathered have been rated:
- LC 22 - Modification or experiment on existing plant. GREEN rating. EDF NGL is implementing enhancements to systems that are potentially susceptible to HEAT effects. We raised concerns during the inspection in relation to the timescales for implementation of required enhancements to safety significant systems. The licensee provided us with a revised programme for implementation of the enhancements by end May 2024. We advised that possible enhancements to increase plant resilience to HEATs need to be recorded and tracked using appropriate means. We observed that EDF NGL’s implementation of engineering change commitments and limitations across the fleet is not timely and plan to follow-up on this matter with EDF NGL fleet.
- LC 23 - Operating rules. GREEN rating. EDF NGL has implemented an operating rule that requires the reactor units to shut down if ambient temperature exceeds 36°C. This operating rule provides margin to claimed plant qualification limits and it is judged there are no cliff-edge effects in terms of plant performance. EDF NGL provided adequate evidence that surveillance routines for operating rule compliance are being completed.
- LC 24 - Operating instructions. GREEN rating. EDF NGL has enhanced its instructions for managing risks from a HEAT event. We identified potential for further enhancement of some safety documentation relevant to HEATs and that operating instructions are less clear for low ambient temperatures. We advised EDF NGL that adequate guidance should be provided to manage risks arising from temperature hazards, including incorporating lessons learned from the HEAT safety documentation. We also identified potential enhancements to HYA and HYB joint arrangements for managing the effects of HEATs across both stations and provided advice to both stations.
- LC28 - Examination, inspection, maintenance and testing. Not Rated. Insufficient evidence gathered during the inspection activity.
Conclusion
The inspection has judged the adequacy of EDF NGL’s arrangements for HEATs against relevant licence conditions. We provided regulatory advice to EDF NGL that some enhancements to aspects of HYA’s station arrangements, and joint arrangements with HYB. Overall the inspection was rated Green (No formal action) as no significant issues were raised.