- Site: Torness
- IR number: 19-126
- Date: December 2019
- LC numbers: 10, 23, 24, 27, 28
Executive summary
Purpose of Intervention
This intervention at EDF Energy Nuclear Generation Limited’s Torness power station, formed part of the ONR Torness Integrated Intervention Strategy (IIS) for 2019/20. It combined two aims:
- To sample the stations arrangements for ‘trip hardening’ i.e. reduction of the frequency of unintended reactor shutdowns and respond as appropriate;
- To undertake a Systems Based Inspection of reactor protection systems.
Interventions Carried Out by ONR
With these aims we sampled the following systems:
- Boiler feed systems;
- Arrangements to protect against marine ingress;
- Flux Detectors.
In the case, of Marine Ingress, the cooling water system was inspected from the condensers to the sea water inlets.
The inspection sampled the implementation of the Licensee’s arrangements at Torness against five licence conditions (LCs). The objective of the inspection was to determine whether the Licensee’s arrangements were adequately implemented and in accordance with the system’s safety case requirements. The LCs were:
- LC10, Training
- LC23, Operating rules
- LC24, Operating instructions
- LC27, Safety mechanisms, devices and circuits
- LC28, Examination, inspection, maintenance and testing
In this SBI, Leakage and Escape of Radioactive Material and Radioactive Waste (SL 34) was not considered in this intervention.
The intervention was performed in line with ONR's guidance requirements (as described in our technical inspection guides) in the areas inspected.
Explanation of Judgement if Safety System Not Judged to be Adequate
On the basis of our sample we consider safety systems to be adequate.
Key Findings, Inspector's Opinions and Reasons for Judgements Made
Licence Condition 10 (Training) and Licence Condition 23 (Operating Rules) - In general we found on the basis of our sample that Torness has adequate arrangements in place to ensure that the three systems are operated, inspected and maintained by trained staff in accordance with the safety case. As such, an inspection rating of Green (no formal action) for LC10 and LC23.
Licence Condition 24 (Operating instructions) - The newly amended procedures sampled were of a good standard with evidence that training and guidance is being followed. We observed that there is an improved focus on human performance with comprehensive training being rolled out across the station. We advised that the station needs to consider how to maintain and embed human performance improvements they have made and observed that the significant reduction in collective experience in central control room staff must be carefully managed. We rated the inspection Green (no formal action) for LC24.
Licence Condition 27 (Safety Mechanisms, Devices and Circuits, SMDCs) and Licence Condition 28 (Examination, Inspection, Maintenance and Testing) - We found that there were positive improvements in place or planned to reduce the impact of marine ingress. We observed that modifications to reduce the impact of quadrant trips were well thought through and that risks remain within the safety case and ALARP. We found the Boiler feed plant to be well maintained with working conditions being good.
A meeting was held to discuss the proposals relating to flux detectors. We observed that recent delays in replacement of the ageing flux were requiring the station to tolerate a degraded situation and runs the risk of putting the station into a half trip state which could ultimately result in a return to service issue.
A walk-down of the Boiler House revealed the presence of a steam leak which had not received adequate prioritisation and through further sampling of the three systems we identified other issues relating to prioritisation of work on safety systems. In light of this observation, we have elected to raise a regulatory issue to follow the station’s investigation into the steam leak. However, on the whole we considered that examination, maintenance and testing met legal requirements. As such, an inspection rating of Green (no formal action) for LC27 and LC28.
Conclusion of Intervention
After considering all the evidence examined during our sample inspections, undertaken against LCs 10, 23, 24, 27 and 28 we judged that the systems we examined and the trip hardening proposals meet the requirements of the safety case. This was communicated to Station management at the close of the inspection. We made some observations for consideration and have raised one new regulatory issue concerning investigation into a defect which as such will be followed to closure through routine interactions with the station.
There were no findings from this inspection that could significantly undermine nuclear safety. At present, no additional regulatory action is needed over and above the planned interventions of Torness nuclear power station as set out in the Integrated Intervention Strategy, which will continue as planned.