Dungeness B - System Based Inspection of the Gas Circulator System
- Site: Dungeness B
- IR number: 19-170
- Date: February 2020
- LC numbers: 10, 23, 24, 27, 28, 34
Purpose of Intervention
The purpose of this intervention was to undertake a multi-disciplinary System Based Inspection (SBI) at EDF Nuclear Generation Limited’s (NGL’s) Dungeness B power station in line with the inspection programme contained in the 2019 - 2020 Site Inspection Plan. The inspection was undertaken by two Fault Studies Specialist Inspectors, a Mechanical Engineering Specialist Inspector, an Electrical Engineering Specialist Inspector, and the Nominated Site Inspector. This SBI concentrated on the Gas Circulators System. The aim of the inspection was to confirm that the Gas Circulators, with associated operating instructions and maintenance schedule, is able to meet the safety case functional requirements.
Interventions Carried Out by ONR
The system based inspection of the Gas Circulators was conducted against compliance with the following Licence Conditions (LCs):
- LC10: Training
- LC23: Operating Rules
- LC24: Operating Instructions
- LC27: Safety Mechanisms
- LC28: Examination, Inspection, Maintenance, and Testing
- LC34: Leakage and Escape of Radioactive Material and Radioactive Waste
The Dungeness B arrangements for monitoring the health of the system were examined. A plant walkdown of key areas associated with the Gas Circulators System was conducted. This included the Gas Circulator Hall for each reactor, containing the gas circulators and associated main motors, very low speed pony motors, and low speed/high speed pony motors. Inspections were conducted, on a sample basis, of the implementation of arrangements against each of the above Licence Conditions.
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
Based on the sample made, I judged that the Gas Circulators System fulfils the safety function and that the safety case has been adequately implemented.
Key Findings, Inspector's Opinions and Reasons for Judgements Made
From the intervention conducted, I summarise the following judgements for each of the Licence Conditions inspected:
- LC 10 (Training) – I examined the training records of a number of individuals associated with the Gas Circulators System. A sample of training records were examined from Electrical Engineering, Mechanical Engineering and Nuclear Safety Group. I found that individuals who were in the process of being trained were supported with appropriate supervision. Permanent and contract staff undertaking activities from the station’s maintenance schedule were suitably qualified and experienced. No significant shortfalls were identified. I therefore assigned a rating of Green (no formal action) for LC 10 compliance.
- LC 23 (Operating Rules) – I examined a sample of Technical Specifications relevant to the Gas Circulators System. The link between the safety case and the Technical Specifications for Gas Circulator vibration monitoring was satisfactory. The Central Control Room Operators demonstrated compliance with the Technical Specifications for Boiler Quadrant Requirements. I assigned a rating of Green (no formal action) for LC 23 compliance.
- LC 24 (Operating Instructions) – Utilising the station simulator, I sampled a recently changed Station Operating Instruction relating to Boiler Tube Leaks. The Simulator Instructor was able to follow the required actions in response to a Boiler Tube Failure from power. A desktop training exercise has been conducted to train operators for Boiler Tube Leaks on a shutdown reactor. My inspection of the Central Control Room confirmed that the operator instructions for responding to a Boiler Tube Leak had been understood. I therefore assigned a rating of Green (no formal action) for LC 24 compliance.
- LC 27 (Safety Mechanisms, Devices and Circuits) – The plant walkdown confirmed that plant and equipment as required by the technical specifications was available. The inspection of arrangements identified that maintenance had been conducted by suitably qualified and experienced personnel within required frequencies. I therefore assigned a rating of Green (no formal action) for LC 27 compliance.
- LC 28 (Examination, Inspection, Maintenance and Testing) – The Gas Circulators System health scores have had a consistently improving trend. A suitable and sufficient auditable trail was demonstrated on the Licensee’s Asset Management System (AMS) with respect to maintenance schedule activities. I therefore assigned a rating of Green (no formal action) for LC 28 compliance.
- LC 34 (Leakage and Escape of Radioactive Material) – This Licence Condition was included in the inspection due to the fact that the Gas Circulator rotating shaft passes through the pressure boundary. Controls on carbon dioxide and oil leakage were sampled with no issues identified that were not already being adequately addressed by the station. I therefore assigned a rating of Green (no formal action) for LC 34 compliance.
The following observations were raised with the station during the inspection:
- A Technical Specifications Commentary was found to contain a reference to a safety case that has not been approved. The station raised Condition Report Number 1175175 to address this minor process compliance concern.
- The labelling of equipment was observed to require further clarity and consistency in some isolated areas. Station advised that additional labelling would be affixed.
Conclusion of Intervention
From the sample inspected, it is judged that compliance against LC 10, 23, 24, 27, 28 and 34 met the required standard; therefore a 'Green' rating was given for all Licence Conditions. The Gas Circulators System is judged to meet the safety case requirements.