System Based Inspection of the Reactor Post Trip Logic System and Oxygen Injection readiness review
- Site: Heysham 1
- IR number: 19-103
- Date: October 2019
- LC numbers: N/A
Purpose of Intervention
The primary focus of this intervention was a planned system based inspection (SBI) of the EDF Energy Nuclear Generation Ltd (EDF NGL) Heysham 1 (HY1) power station reactor post trip logic (RPTL) system, which was undertaken as part of the HY1 integrated intervention strategy (IIS) plan.
Interventions Carried Out by ONR
The nominated Office for Nuclear Regulation (ONR) HY1 site inspector, an ONR control and instrumentation (C&I) specialist inspector and two ONR electrical specialist inspectors undertook a SBI of the HY1 RPTL system in order to judge whether it was able to fulfil its safety duties (safety functional requirements) in line with the safety case.
The RPTL system automatically starts-up / shuts-down essential plant in a defined sequence following a reactor trip in order to control post-trip temperature transients and ensure adequate decay heat removal.
Through sampling of associated operating and maintenance documentation, a plant walkdown and discussions with relevant HY1 staff we examined the performance of the RPTL system against the following Licence Conditions (LCs), which are applicable provisions of the Energy Act 2013:
- LC 10 – Training;
- LC 23 – Operating rules;
- LC 24 – Operating instructions;
- LC 27 – Safety mechanisms, devices and circuits (SMDCs);
- LC 28 – Examination, inspection, maintenance and testing (EIMT).
It should be noted that LC 34 (leakage and escape of radioactive material and radioactive waste) was not considered during this inspection, as the RPTL system does not contain radioactive material.
The intervention was performed in line with ONR's guidance requirements (as described in our technical inspection guides) in the areas inspected.
Two International Atomic Energy Agency (IAEA) Integrated Regulatory Review Service (IRRS) UK mission inspectors also attended the first day of the SBI in an observatory capacity only.
During the two days of the SBI, the C&I specialist inspector also held a number of ad hoc discussions with EDF NGL personnel regarding the status of HY1 oxygen injection system commissioning activities.
Explanation of Judgement if Safety System Not Judged to be Adequate
Key Findings, Inspector's Opinions and Reasons for Judgements Made
The key findings of our SBI of the RPTL system are:
- LC 10 – Training: We examined the training records of a number of personnel involved with the maintenance and operation of the RPTL system, and judged that they were suitably qualified and experienced personnel (SQEP). We therefore assigned an IIS rating of Green (no formal action) for LC 10.
- LC 23 – Operating rules: We reviewed the main technical specifications (tech specs) associated with the RPTL system and judged that the specified limiting conditions for operation (LCOs) adequately reflected those specified in the safety case. Based on discussions with the central control room (CCR) supervisor and a reactor desk engineer (RDE) we also judged that compliance with the associated surveillance requirements was being achieved. During the inspection, on one occasion, the CCR supervisor and RDE found it difficult to interpret one part of the main tech specs. The CCR supervisor and RDE both stated that they would consider if this was necessary to add clarification and / or context and whether simulator training was necessary. It should be noted that we did not consider this issue to present an immediate risk to nuclear safety and that we will track its progress to resolution, as part of normal regulatory business. We therefore assigned an IIS rating of Green (no formal action) for LC 23.
- LC 24 – Operating instructions: We examined the main station operating instructions (SOIs) associated with the RPTL system and discussed their application with the CCR supervisor and a RDE. As a result we judged that adequate operating instructions were in place to support RPTL system operations. We therefore assigned an IIS rating of Green (no formal action) for LC 24.
- LC 27 – SMDCs: During the SBI we reviewed several operating and maintenance documents, undertook a plant walkdown and spoke to a number of stakeholders. As a result we judged that the RPTL system was connected correctly, was in working order, and was being adequately maintained. We also judged that its configuration was being adequately controlled and that adequate numbers of spares were available. We therefore judged the IIS rating for LC 28 to be Green (No formal action).
- LC 28 – EIMT: We reviewed a number of RPTL system maintenance work instructions (WIs), and associated work order cards (WOCs) and checksheets. As a result we considered that the associated maintenance tasks had been adequately defined and had been carried out as specified. We did note a number of shortfalls and raised these with the system engineer (SE) who was responsible for the RPTL system. The SE accepted our findings and stated that he would take steps to address the shortfalls. It should be noted that we did not consider these shortfalls to present an immediate risk to nuclear safety and that we will track their progress to resolution, as part of normal regulatory business. We also found that each of the sampled maintenance tasks had been completed in line with the periodicity specified in the maintenance schedule. We therefore judged that the RPTL system was being adequately examined, inspected, maintained and tested. We therefore judged the IIS rating for LC 28 to be Green (No formal action).
Conclusion of Intervention
From the evidence sampled during this SBI against LCs 10, 23, 24, 27 and 28, we judged that the RPTL system was able to fulfil its safety duties (safety functional requirements) in line with the safety case.
There are no findings from this intervention that could significantly undermine nuclear safety at HY1. At present, no additional regulatory action is needed over and above the planned interventions at HY1, as set out in the HY1 IIS, which will continue as planned.