The purpose of this intervention was to conduct a benchmark inspection of the arrangements in place at Dungeness B power station (DNB) to manage the integrity of concealed pipework, with an emphasis placed upon how corrosion is managed. The work was carried out as part of the planned intervention task sheet TS015 - "Pipework - Material Condition - Corrosion Under Insulation and Concealed/Buried Systems".
I carried out this inspection accompanied by an ONR Project Inspector, with the nominated Site Inspector present for the close out session. The inspection was took place on 12 and 13 April 2016 and involved discussions with a number of EDF Nuclear Generation's (NGL) employees responsible for the operation and safety of the plant, plant walk downs were also undertaken.
The objective of the inspection was to obtain information relating to NGL's arrangements for managing corrosion of their concealed pipework, in order to identify any areas of relevant good practice, or shortfalls to our expectations. I concentrated my intervention on items I judged important to nuclear safety, focussed upon Structural Integrity.
The inspection reviewed the procedures, roles and responsibilities of key staff and sampled compliance arrangements against license conditions (LC) LC10 (training) and LC28 (examination, maintenance, inspection and testing) to judge the adequacy of the arrangements in place.
Although areas for improvement have been identified, it is acknowledged that NGL are introducing measures to address them. We judged that the arrangements and their implementation, associated with concealed pipework and corrosion under insulation currently conform to a green rating, but recommend further monitoring once the revised processes have been adopted by DNB.
DNB were able to demonstrate that processes exist to establish the integrity of concealed pipework, particularly relating to external corrosion and corrosion under insulation. Clear progress had been made since previous visits to station and it is apparent that consistent resource is being allocated to the inspection activity.
The Corrosion Co-ordinator demonstrated good awareness of her responsibilities in the role, identified within NGL Company Technical Specifications. However, it was clear that additional duties placed upon her had the potential to jeopardise her effectiveness as Corrosion Co-ordinator. This had been recognised by senior staff at DNB, and we were made aware of measures being implemented for a more team based approach to the management of concealed systems and their associated corrosion.
Training provided to NGL staff involved in the process was deemed to be adequate, with areas of good practice noted, particularity relating to corrosion focussed plant walk down training. Maintenance schedule records and inspection results for selected areas of CO2 pipework with nuclear safety significance were available for review, although the process of obtaining the information was complex.
The greater awareness of corrosion issues demonstrated by System Engineers and the increase in inspection activity by the various projects concerned with pipework integrity will be likely to result in an increase in remedial actions raised on work order cards. During the visit we were made aware of instances where defect remediation had been re-prioritised by work management staff, potentially not fully qualified to make these judgements and without prior consultation with the work order card originator. This was identified as an area for improvement during our inspection. It is also acknowledged that NGL have recognised this shortfall recently and provided tailored awareness training to work management staff in order to minimise the risk of defects becoming significant to nuclear safety due to their ineffective re-prioritisation.
I had been made aware of a previous steam leak from plant located in the region of plant item 22/WP/D2355, associated with a condensate recovery unit. This leak had been identified during an ONR System Based Inspection in 2014. I revisited the area and it was clear that the leak had not been rectified. I was informed that the remediation had been re-prioritised on a number of occasions by the Work Management team, without consulting the appropriate System Engineer. I explained to DNB staff that I judged this an example that the process for rectifying defects at DNB could fail. NGL have subsequently confirmed that the area has now been provided with suitable barriers to prevent harm to personnel and also confirmed that the leak does not pose a risk to nuclear safety. NGL have agreed to raise a Condition Report to establish the series of events and areas for improvement relating to the re-prioritisation of this steam leak, the results will be made available to ONR for review.
Although areas for improvement have been identified, it is acknowledged that NGL are introducing measures to address them. We judged that the arrangements and their implementation, associated with concealed pipework and corrosion under insulation currently conform to a green rating.
DNB have demonstrated that processes exist to manage the integrity of their concealed pipework with relation to corrosion. However, a number of significant modifications to the process are either planned, or are in the process of implementation. It is therefore recommended that ONR revisit DNB at a suitable future date once the revised processes have been implemented, to review and monitor progress.
A list of key findings and actions from this intervention has been provided to DNB for their consideration and resolution. One category 4 issue has been raised to track the progression of the actions raised during the visit and to prompt a revisit to DNB at a suitable future date.