Date(s) of inspection:
- November 2022
Aim of inspection
The aim of this inspection was to gain confidence in the use of ESOP (Essential Systems Outage Program) Risk Monitor for Risk Informed Decision Making at Torness Nuclear Power Station. This was a planned intervention and part of the 2022/2023 ONR integrated intervention strategy for operating reactors.
Subject(s) of inspection
- LC23 – Operating rules – Rating: Green
- LC24 – Operating instructions – Rating: Green
Key findings, inspector’s opinions and reasons for judgement made
A risk monitor uses the station Probabilistic Safety Analysis (PSA) risk model to provide real-time risk information on current and planned plant states. This information allows for risk informed operational and work planning decisions to be made. EDF NGL currently use risk monitors at Heysham B (HYB), Torness (TOR) and Sizewell B (SZB).
HYB and TOR currently use the Essential Systems Outage Program (ESOP) risk monitor for the following primary purposes:
- Technical Specification and Limits and Conditions of Operation (LCO) compliance
- Operator aid to identify applicable plant conditions and LCOs
- Provide risk information to operators and work planners to inform decision making
EDF NGL have launched the “ESOP Stabilisation project” which aims to upgrade the ESOP Risk Monitor Software at HYB and TOR. In parallel with this project, ONR is undertaking Risk Monitor inspections at HYB and TOR and a series of Level 4 engagements to gain confidence in the use of ESOP for risk informed decision making and to ensure that the ESOP Stabilisation project will achieve an updated Risk Monitor that is fit for purpose through to End of Generation (EoG) at HYB and TOR.
At Torness Nuclear Power Station, NGL demonstrated how ESOP is used for managing emerging plant unavailability and how it is used for work planning. I sampled a number of ESOP Records for previous plant unavailability scenarios and Nuclear Safety Group (NSG) assessments where ESOP results were used to extend action completion times. From the discussions with users and sampling records:
- I found that the users at station (Central Control Room (CCR) operators, Work Management Engineers and NSG) are experienced and confident in using ESOP to comply with operating rules and operating instructions.
- In my opinion, adequate arrangements were available to integrate the use of ESOP into station operations.
- The inspection also highlighted that ESOP is integral to the day-to-day operation at TOR. As such, it is necessary that steps are taken to ensure future support from Suitably Qualified and Experience Personnel (SQEP) for ESOP software and the use of the latest TOR PSA model in ESOP. I consider it essential that these issues are addressed in a timely manner to ensure that ESOP is fit for purpose through to the end of generation at TOR.
The inspection demonstrated how ESOP is used to comply with station Operating Rules and Operating Instructions required to manage emerging plant unavailability, extension of action completion times and work planning at TOR. In my opinion, adequate arrangements are available to integrate the use of ESOP into station operation. I judge that the users of ESOP at station are suitably qualified and experienced in using ESOP to comply with the arrangements. Therefore, in my opinion, an inspection rating of GREEN is merited against LC23 (Operating Rules) and LC24 (Operating Instructions).
The inspection also highlighted that ESOP is integral to the day-to-day operation at TOR. Whilst the ESOP software is judged adequate for current purposes, it has a number of known issues and shortfalls, some of which has led to the most up-to-date TOR PSA model not being used for decision making at station. It is also necessary to ensure that sufficient SQEP support for ESOP software is available through to EoG. Given the importance of ESOP to the day-to-day plant management and the fact that an ageing plant will increase the use of ESOP (necessitated by increased equipment failures and increased maintenance activities) I consider it essential that these issues are addressed in a timely manner via the ESOP Stabilisation Project.
I identified a number of points of good practice but also made a number of observations, which were conveyed to the licensee in the post-inspection de-briefing meeting.