The purpose of the Intervention was to allow the Licensee, EDF Energy Nuclear Generation Ltd (EDF NGL), to update the Office for Nuclear Regulation’s (ONR’s) fuel performance assessor with progress on management of Carbon Deposition (CD) in the boilers of the Advanced Gas Cooled Reactor (AGR) fleet. This is part of an ongoing dialogue with the Licensee on this topic, forming a part of ONR’s overall Carbon Deposition Intervention. The Intervention was conducted under Licence Condition 23 (Operating Rules) i.e. in ensuring that the Licensee is continuing to secure its safety case against the challenges posed by CD to the boilers.
The Intervention (performed under Licence Condition 23 i.e. Operating Rules) was conducted at EDF NGL Barnwood, via a number of presentations with resultant discussions around this presentational material. I note that the presentations themselves were of a good quality and all discussions were conducted in an open and transparent manner.
I judge that the Licensee is making good progress across the AGR fleet in the introduction of mitigating strategies (i.e. to clean CD from the boiler tubes) to protect the boilers against the safety challenges posed by CD. Evidence was produced, demonstrating that the mitigating strategies, deployed to date, are having a positive beneficial effect and are reducing the magnitude of the safety challenges. Plans were also highlighted showing how these mitigating strategies will continue to be deployed across the fleet (where required) and these appeared both pragmatic and timely.
However, the mitigators introduced are also causing some unwanted side effects (e.g. temperature tilts across the boilers due to uneven CD cleaning), which in turn pose challenges to components in the boilers that were not designed to ‘see’ the higher temperatures they are now experiencing. I was pleased to see the depth of work that has been undertaken to date to address these problems and the forward plans for in-core improvements to be made on the Station where the challenges are most pronounced. These plans appear to have an appropriate urgency and focus.
Another side effect from one of the introduced mitigators is presently causing operational difficulties at Torness (TOR) and also has the potential to challenge the Station’s aerial effluent discharge authorisations. Again I was pleased to see that these problems have been promptly and successfully addressed and that an engineered solution is to be implemented shortly.
I judged that the meeting had been positive, with the Licensee able to report some strong progress. I will maintain engagement with the Licensee to continue to monitor this progress, but do not judge that any regulatory action is required at this juncture.
N/A.