Executive summary
- Date(s) of inspection: April 2024
Aim of inspection
This was a planned inspection of EDF Nuclear Generation Limited's (NGL’s) implementation of 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 HYB.
This inspection is one of several ONR activities relating to HEATs and the associated regulatory issue (RI). The RI was raised following the July 2022 elevated temperature event that revealed gaps in the licensee’s relevant safety cases, 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.
Subject(s) of inspection
- LC22 - Modification or experiment on existing plant - Rating: Not rated
- 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 were informed prior to the inspection activity that the implementation of the station’s HEAT Justification for Continued Operation (JCO) and updated arrangements was delayed. We therefore inspected existing arrangements relevant to HEATs, the draft JCO and associated potential future actions, and planned updates to operational arrangements for managing risks from HEATs. We expect the update arrangements to be implemented before summer 2024 when the risk of a HEAT event is at its greatest. A plant walkdown of systems potentially susceptible to HEATs was undertaken informed by HYB’s safety documentation.
Only those LCs for which sufficient evidence was gathered have been rated.
- LC22, Modification or experiment on existing plant – Not Rated. Insufficient evidence was gathered during the inspection activity. The JCO is still progressing through due process and has not been fully implemented. Draft versions of the associated arrangements were available. We provided advice in relation to future actions stemming from the draft HEAT JCO. We will follow-up on the implementation of actions via the forthcoming Chief Nuclear Inspector’s (CNI’s) themed inspection on climate change.
- LC23, Operating rules – Green. This rating was awarded on the basis that EDF NGL has existing arrangements that require the reactor units to shut down based on system availability if ambient temperature exceeds 36°C. The draft arrangements will formalise this requirement as an operating rule. Margin exists between the shutdown temperature and claimed plant qualification limits for safety systems, and it is judged there are no cliff-edge effects in terms of plant performance. We expect the updated arrangements to be implemented before the summer season. EDF NGL provided adequate evidence that adverse weather checks are being completed daily.
- LC24, Operating instructions – Green. This rating was awarded on the basis that EDF NGL has existing arrangements for responding to HEAT events. The arrangements have incorporated lessons learned following the July 2022 elevated temperature event. Operating instructions are being further enhanced to reflect changes resulting from the draft JCO. We advised EDF NGL of potential improvements that are judged practicable.
- LC28, Examination, inspection, maintenance, and testing – Not Rated. Insufficient evidence gathered during the inspection activity. EDF NGL is addressing several observations we made during the plant walkdown.
Conclusion
The inspection has judged the adequacy of EDF NGL’s arrangements for HEATs against relevant licence conditions. Overall, the inspection was rated Green (No formal action) as no significant issues were raised. We advised EDF NGL that some enhancements to HYB’s station arrangements are judged practicable. 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. EDF NGL raised Condition Reports and/or Work Requests during this activity to track and address such matters. The ONR nominated site inspector intends to follow-up on this as normal business.