Executive summary
Date(s) of inspection: July 2024
Aim of inspection
The purpose of the intervention was to inspect compliance with licence condition 11, emergency arrangements, at EDF Energy Nuclear Generation Ltd.’s Sizewell B power station.
Subject(s) of inspection
- LC11 - Emergency arrangements - Rating: Green
Key findings, inspector's opinions and reasons for judgement made
ONR assessed the Level 1 emergency exercise 'STILETTO' at EDF Energy Nuclear Generation Ltd. (NGL) Sizewell B power station.
The exercise scenario consisted of a steam generator tube rupture with the reactor containing failed fuel which resulted in an off-site release of radioactivity. Additional challenge was introduced whilst conducting electrical breaker racking which resulted in a 415V ark flash event leading to an operator fatality and another operator sustaining significant burns and shrapnel injuries. There were also a number of equipment failures and a loss of off-site power as a consequence of the reactor trip.
The licensee's emergency response achieved the following key outcomes:
- Established three on-site command centres at the Main Control Room (MCR), Emergency Control Centre (ECC) and Access Control Point (ACP)) together with support from the corporate Central Emergency Support Centre (CESC) located off-site.
- Completed a full site muster, accounting for all persons.
- Located and transferred the casualty to the medical facility for further medical assessment and treatment.
- Established a quarantine around the fatality area and implemented crime scene management
- Made timely and appropriate declaration of an Off-Site Nuclear Emergency (OSNE).
- Deployed and connected the high pressure pump deployable back-up equipment.
Overall, the licensee effectively managed the event, noting that some elements of the response could have been implemented in a more timely manner. In addition we identified a number of minor areas for future enhancement to the licensee's emergency response and have raised a level 4 regulatory issue to monitor the licensee’s progress.
Conclusion
ONR acknowledged that the exercise scenario was challenging and incorporated diverse aspects which added to the level of challenge.
Overall, we judged that the licensee's performance as adequate and awarded a green (no formal action) inspection rating against licence condition 11 - emergency arrangements.