During the reporting period 1 October 2023 – 31 December 2023 there was one event at a nuclear licensed sites within Great Britain that met the Ministerial Reporting Criteria (MRC) as defined within the Nuclear Installations (Dangerous Occurrences) Regulations 1965 and ONR guidance in relation to notifying and reporting incidents.
Key information
- Incident ID: INF-3582 and INF-3614
- Site/Consignor: EDF NGL Heysham 1
- Date of occurrence: 23/12/2023
- ONR incident category: NS04, AN01, CS02
- INES rating: 0 Below Scale
- ONR governance category: 2a
Incident description
At Heysham 1 Power Station in Lancashire on 23 December 2023 at 4.16am, a valve controlling the flow of superheated steam from one quadrant of Reactor 1 failed, resulting in steam leak.
The reactor was being returned to service and the valve was in the process of being opened to allow main steam to supply the turbine.
The reactor was tripped and post-trip cooling established. The Central Control Room declared a site incident at 4.21am. No staff were present in the vicinity of the failed valve and all station personnel were accounted for by 4.39am.
There was no harm to workers, the public or the environment as a result of the incident.
The nuclear safety significance of the event was minor. The steam leak was well within the range of faults that the plant is designed to deal with. There were other valves to isolate the steam flow and the plant damage around the failure was not nuclear safety significant.
The conventional health and safety significance of the event was moderate. The area around the valves is frequently occupied by staff, so this event had the potential to cause serious or fatal injuries to workers.
Ministerial Reporting Criterion
Although the specific incident has not generated any media coverage, the resulting impact (shutdown of all four units at Heysham 1 and Hartlepool power stations) has resulted in media coverage. ONR’s decision to serve an Improvement Notice (issued to EDF on 23 January 2024) following preliminary enquiries into the event, is likely to attract further media attention.
Dutyholder’s response
The dutyholder implemented its emergency arrangements for a site incident. Notifications were made to a number of organisations including ONR. Emergency services also attended the site in support but were not deployed onto the plant. Station emergency teams were deployed to the scene to assess damage. The site incident was stood down at 12.30pm the same day and an event recovery organisation established.
Following the incident more information became available about the mechanism of failure which included safety concerns associated with this type of valve in use on other reactor sites. This led to the decision to shutdown Heysham 1 Reactor 2 in December 2023 and Hartlepool Reactors 1 and 2 in January 2024.
EDF has commenced its own investigation.
ONR’s action
ONR monitored the licensee’s response to the incident, noting the promptness and effectiveness of the site’s emergency response, the support from Heysham 2 and EDF’s central support centre in Barnwood.
ONR is content with EDF’s safety-based decision making following the event, which sought to understand the mechanism failure and the safety implications for the other reactors with this type of valve. ONR is also content with the timeliness and openness of the communication it has had with EDF.
ONR undertook preliminary enquiries into the event . The information collected resulted in an Improvement Notice being served on EDF on 23 January 2024, relating to the maintenance of systems and the duty of EDF to ensure so far as is reasonably practicable, the health, safety and welfare at work of all its employees.
ONR is considering which safety cases it will assess prior to any reactor return to service at Heysham 1 and Hartlepool.
ONR is aware that this type of valve may be in service in other power stations and process plants. ONR will be communicating relevant information associated with the event more widely in accordance with its process.