Office for Nuclear Regulation

Dungeness B - R22 Outage - Mechanical Engineering Inspection

Executive summary

Purpose of intervention

This report records the findings of the ONR Mechanical Specialists’ intervention visit to Dungeness B (DNB) Nuclear Power Station for the 2015 Reactor 22 periodic shutdown. The intervention was undertaken to confirm the adequacy of mechanical engineering related activities conducted by the Licensee to comply with the requirements of Licence Condition (LC) 28, Examination, Inspection, Maintenance and Testing (EIM&T), against a sample of nuclear safety significant reactor components.

This report provides supporting evidence to inform the ONR decision relating to the issue of a Licence Instrument for Consent for return to service of Reactor 22 at Dungeness B on completion of the work undertaken during the outage.

In addition to the above outage inspection, this report follows up of the findings from the System Based Inspection of Ponds and Flasks Systems in March 2015 (TRIM Ref 2015/86308) which recorded an IIS rating of 4 – Below Standard, through a more detailed LC28 inspection of the maintenance arrangements for the Fuel Pond Flask Handling Crane. 

Interventions Carried Out by ONR

The intervention consisted of on-site meetings and a plant inspection with relevant staff from NGL Energy Nuclear Generation Limited to determine the adequacy of the work being undertaken on Dungeness B Reactor 22 in complying with the requirements of LC 28. The activities examined were selected due to their nuclear safety significance and agreed in advance of the visit with the Dungeness B station and site inspector.

The inspection included:

The inspection was supported by inspection visits to the following areas:

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

Not applicable.

Key Findings, Inspector's Opinions and Reasons for Judgements Made

Based on my sampling, I am satisfied from a mechanical engineering perspective that during the Dungeness B 2015 Outage:

  1. EIM&T associated with Gas Circulators is being adequately controlled.    
  2. EIM&T associated with Safety Significant Valves is being adequately controlled. I have identified an area for improvement associated with safety significant valves relating to completeness of records. I will follow this item up separately from the outage, and I do not consider this finding to be safety significant at this time.
  3. EIM&T associated with Control Rod Assemblies is being adequately controlled. I consider the quality of the EIM&T documentation for this equipment to be of a good standard and will use this as an example for future interventions across the NGL fleet of reactors.
  4. Adequate EIM&T is undertaken on the control rods, in line with the requirements of the safety case. Also, suitable and sufficient records are been kept and monitored to identify problems both re-actively and pro-actively.

Based on my sampling, I am satisfied that the arrangements for EIM&T carried out on the Flask Crane are appropriate and adequately controlled.  This closes out the concerns raised during the System Based Inspection of Ponds and Flasks Systems by the mechanical inspector, which receive an IIS rating of 4 – Below Standard.

Conclusion of Intervention

This report presents the findings of the mechanical engineering intervention of the LC28 EIM&T arrangements in place to support the 2015 Dungeness B Reactor 22 periodic shutdown.

Based on my sampling undertaken as part of this intervention, I am satisfied that the LC 28 arrangements in place are adequate and I am satisfied they are overall adequately implemented.  I will take this conclusion through to my Mechanical Engineering Assessment Report for the 2015 Dungeness B Outage.

Based on my sampling undertaken as part of this intervention, I am satisfied that the LC28 arrangements in place for EIM&T of the Flask Crane in the Fuel Pond Area are appropriate and adequately controlled.

In my judgement, there are areas for improvement associated with maintenance activities. Adequacy of record keeping and suitability of foreign material exclusion standards are two examples of these.  I will follow up these matters up as part of normal regulatory business and have raised a number of ONR Level 4 regulatory issues to progress them.

Based on my intervention I judge that an IIS rating of 3 – Adequate is appropriate for all parts of this intervention.