Office for Nuclear Regulation

Sizewell B – Inspection ID: 52804

Executive summary

Date(s) of inspection:

June 2023

Aim of inspection

Observation of the annual level 1 demonstration exercise to confirm that Sizewell B’s emergency arrangements remain effective.

Subject(s) of inspection

  • LC 11 – Emergency arrangements – Rating: GREEN

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

ONR observed and assessed the level 1 emergency exercise ‘WASHINGTON’ at the EDF Energy Nuclear Generation Ltd. (NGL) Sizewell B power station.

The scenario involved a significant steam leak, failure of the main steam isolation valve and subsequent fuel failure resulting in an off-site release. The licensee’s response:

  • Established three on-site command centres (Main Control Room (simulator), Emergency Control Centre and Access Control Point) and the corporate Central Emergency Support Centre.
  • Assessed the plant conditions and terminated the steam leak in a timely manner.
  • Located, assessed, rescued and treated four casualties.
  • Completed a full site muster, accounting for site personnel in a timely manner.
  • Made appropriate declarations, escalating to Off-Site Nuclear Emergency.

Areas for improvement were identified, associated with:

  • A lack of urgency throughout the command chain.
  • Systematic casualty assessment and handling.
  • Management of high ambient temperatures.

ONR were satisfied that the exercise objectives and performance indications in the licensee’s scenario were largely met.


ONR judged that exercise ‘WASHINGTON’ was an adequate demonstration of Sizewell B’s emergency arrangements and rated the inspection against Licence Condition 11 as Green (no formal action).