- Site: Devonport
- IR number: 21-001
- Date: April 2021
- LC numbers: 10, 23, 24, 27, 28, 34
Executive summary
Purpose of Intervention
The Office for Nuclear Regulation (ONR) undertakes all interactions at the Devonport Licensed Site (operated by Devonport Royal Dockyard Limited (DRDL)), in accordance with ONR’s integrated intervention strategy (IIS).
The purpose of this intervention was for ONR to conduct a system based inspection, to examine whether the Licensee’s safety case claims, relating to the 60Hz Nuclear System have been adequately implemented.
This intervention was undertaken remotely, by ONR electrical specialist inspectors. A member of the Licensee’s Independent Nuclear Oversight team supported the intervention and conducted certain site-based activities as required. The Defence Nuclear Safety Regulator (DNSR) also participated in the intervention.
Interventions Carried Out by ONR
For this intervention, ONR performed a planned safety case informed system based inspection of the safety systems and circuits associated with the 60Hz Nuclear System, to judge performance against the safety functional requirements and examine the adequacy of implementation of the safety case. The following systems and components were sampled by this intervention:
- 60Hz high voltage ring mains and switchgear (including control mimics)
- On-site fixed 60Hz diesel generators
- 60Hz high voltage to low voltage transformers
- 60Hz low voltage cabling to shore supply cable change boxes
- Alternating current to direct current rectifiers
- Direct current cabling to shore supply cable change boxes
- Nuclear Supervisory, Control and Data Acquisition (SCADA) system
Through sampled examination of the arrangements made for the 60Hz Nuclear System safety systems and components, ONR performed compliance inspections against the following licence conditions (LCs) where applicable:
- 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)
- LC 34 – Leakage and Escape of Radioactive Material and Radioactive Waste
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
The Licensee has demonstrated that the safety systems and circuits sampled in relation to the 60Hz Nuclear System are able to fulfil their safety functional requirements adequately, in line with the safety case.
Key Findings, Inspector's Opinions and Reasons for Judgements Made
Based on the specific areas sampled during the course of the inspection, I found that overall, the Licensee has adequate arrangements in place to ensure that the safety systems and circuits associated with the 60Hz Nuclear System are operated and maintained in accordance with the appropriate safety cases and safety functional requirements. Ratings for each of the LCs are as follows:
- LC 10 (training) – IIS Rating GREEN. I judged that from the Operators and maintainers’ training records sampled and demonstrated, personnel were adequately trained and had the competencies required to operate and maintain the 60Hz Nuclear System. Good practice was also demonstrated in relation to training and ensuring operators and maintainers continue to have the relevant competencies for their roles.
- LC 23 (operating rules) – IIS Rating GREEN. I judged, from the presentations and demonstrations given of the tools and processes in place, that the limits and conditions of operation from the safety cases are understood and implemented, such that operators can operate the plant within those limits.
- LC 24 (Operating instructions) – IIS Rating GREEN. In the areas sampled, I judged that the operating instructions were consistent with the claims made on the system and the limits and conditions of operations. It was demonstrated that, in general, the operating instructions described how tasks will be carried out and contained all necessary prerequisites, checks, precautions and actions to take.
- LC 27 (Safety mechanisms, devices, and circuits) – IIS Rating AMBER. Based on the evidence sampled during this inspection, I judged that DRDL has not fully met specific legal requirements of LC 27 in that certain safety mechanisms, devices and circuits (SMDCs) associated with the 60Hz Nuclear System have reduced functionality and are not in good working order. The reduction in functionality has led to DRDL introducing substituted arrangements to ensure that the plant and equipment is in adequate condition to perform its’ safety function. It was not clear at the time of inspection, the DRDL plans for restoring the functionality of the affected SMDCs. I judged, that although specific shortfalls have been identified with respect to LC 27, within the context of the overall system based inspection, no significant shortfalls in the delivery of nuclear safety were identified that would prevent the 60Hz Nuclear System from providing its’ safety function if called upon.
- LC 28 (examination, inspection, maintenance and testing) – IIS Rating AMBER. I judged that the Licensee has not fully met specific legal requirements of LC 28 (1) in that maintenance of an SMDC is not being carried out as required by the maintenance schedule due to the fragility of the equipment. It was not clear at the time of the inspection, the DRDL plans for re-introducing maintenance of this SMDC in order to ensure its’ nuclear safety function. I judged that although a specific shortfall has been identified with respect to LC 28, within the context of the overall system based inspection, no significant shortfalls in the delivery of nuclear safety were identified that would prevent the 60Hz Nuclear System from providing its’ safety function if called upon
- LC34 (leakage and escape of radioactive material and radioactive waste – IIS Rating N/A. LC34 rating not awarded, as I judged that this licence condition was not sufficiently relevant to the safety systems and components under consideration.
Conclusion of Intervention
From the evidence sampled during the inspection, I consider that overall, the safety systems and circuits associated with the 60Hz Nuclear System meet the claims in the relevant safety cases and that there are no findings from this inspection that could significantly undermine nuclear safety.
Specific shortfalls against ONR technical inspection guide NS-INSP-GD-027 expectations were recorded in relation to ensuring that equipment performing a safety function is in good working order. I judged, that although specific shortfalls have been identified with respect to LC 27, within the context of the overall system based inspection, no significant shortfalls in the delivery of nuclear safety were identified that would prevent the 60Hz Nuclear System from providing its’ safety function if called upon.
A specific shortfall against ONR technical inspection guide NS-INSP-GD-028 expectations was recorded in relation to ensuring that plant and equipment is maintained in accordance with a maintenance schedule. I judged that although a specific shortfall has been identified with respect to LC28, within the context of the overall system based inspection, no significant shortfalls in the delivery of nuclear safety were identified that would prevent the 60Hz Nuclear System from providing its’ safety function if called upon.
An ONR Regulatory Issue has been raised to track progress of the identified shortfalls. ONR inspectors will conduct further engagements with the Licensee during the progression of the regulatory issue. No additional regulatory action is needed over and above ONR’s planned interventions as set out in the ONR integrated intervention strategy plan.