Dungeness B has, for some years suffered from failures of a small number of individual fuel pins within the fuel elements in its two reactor cores. Upon such failures occurring, the fuel is removed from the reactor core and the individual fuel elements are sealed in bottles (steel flasks used to isolate the failed fuel from the Fuel Storage Pond water) and the bottles are then stored in the Fuel Storage Pond awaiting export to Sellafield. The licensee, EdF Energy Nuclear Generation (NGL) has made engineering changes to the fuel which has progressively reduced the occurrence of these failures, such that both reactor cores at Dungeness B are presently failure free. However, numbers of bottles of failed fuel are still held in the Dungeness B Fuel Storage Pond.
The key focus of the intervention was to seek information on the licensee's progress with the export of bottled non-intact fuel from the Fuel Storage Pond at Dungeness B and on its on-going management of the stored bottles. Current holdings of such bottled fuel in the Fuel Storage Pond are the subject of an Office for Nuclear Regulation Issue on its Issues Database. However, during my visit I also took the opportunity to engage with key station personnel on a range of fuel related topics. Additionally, I sought the views of the licensee, as to how the recently created role of 'Criticality Specialists' at Dungeness B was developing and maturing, and more generally I sought evidence that the station was continuing to maintain a focus on criticality safety during its operations.
I conducted this intervention by visiting key areas of the Dungeness B plant, examining plant records and documentation, and by holding discussions with key licensee personnel.
No Systems Based Inspection was conducted and hence this heading is not relevant in this Intervention Record.
NGL presented documentary evidence to me that demonstrated that there is a clear and timely plan in place for export from the station of its bottled failed fuel stocks held within its Fuel Storage Pond. There are no current operational constraints to export of the bottled fuel from the station, although contractual and other difficulties, outside of NGL's control, can sometimes delay planned exports. However, the licensee was also able to demonstrate that work is in hand to justify an extension in the claims it presently makes on the seals on the bottles in pond storage. Should a bottle seal fail this could release contamination into the Fuel Storage Pond, although there is no evidence of such an occurrence in the operating history of the station. Accordingly, NGL presented evidence which demonstrated that it has a robust pond water sampling regime in place (which would hence quickly detect such a failure) and ion-exchange resin stocks are held on the station which would be deployed to promptly effect pond water clean-up. On the basis of the evidence presented to me, I am content that NGL is adequately managing its failed fuel stocks on the station and I propose to down-grade the level of importance currently attached to the Office for Nuclear Regulation Issue.
A visit to the station's New Fuel Store confirmed that whilst the station has significant holdings of such items, these are clearly marked and appropriately segregated from other operational items in the store. From my discussions with station personnel it was clear that adequate plans are in place to export these items from the station but delays are being occasioned by contractual negotiations with Springfields Fuels Ltd, which lie outside the station's control. I agreed that I would pursue this matter further with the Nuclear Fuel Liabilities Group at the Barnwood corporate centre.
I questioned station personnel on the current failed fuel holdings in the Buffer Storage Tubes and was pleased to learn that only one failed fuel assembly is held in the Tubes and that this should be sent for dismantling and bottling circa March 2015. I was also pleased to see documentary evidence that Dungeness B has an ability to 'sniff' for activity in the Buffer Storage Tubes. This is not possible on all of the Advanced Gas Cooled Reactor stations and is of importance if refuel operations have to be carried out with unlocated failed fuel in the reactor core (which could be inadvertently removed to the Buffer Storage Tubes). 'Sniffing' of the tubes in such circumstances helps to protect the down-stream Fuel Storage Pond.
The Burst Can Detection (BCD) equipment refurbishment at Dungeness B is now nearly complete and few operational problems were reported with the refurbished equipment. The Gaseous Activity Monitoring equipment was reported to be functioning adequately with Dungeness B being the second station in the fleet programmed to have its system substantially refurbished by a fleet-wide project (likely to be completed in 2016). I am content with the station's current equipment availability for the detection of failed fuel in its reactor cores.
Discussions with station personnel revealed that the plant has recently undergone an intensive period of defect tracking and rectification; obsolescence issues are well recognised and are being managed appropriately (several examples were presented to me of obsolete plant items that have recently been replaced with modern equivalents). The bottling plant has been improved as recently as January 2015 and is working well. I am content with the current status of this facility.
I obtained good evidence from my discussions with station personnel that the role of 'Criticality Specialist' on the station is functioning as per the requirements of the job specification and some instances of early benefits provided by the role were provided. I was also pleased to see evidence that criticality refresher training for fuel route operatives is taking place. From the evidence presented I am content with the present 'health' of criticality safety at the station.
I visited this facility in 2013 as a part of an intervention, across the Advanced Gas Cooled Reactor fuel routes, conducted by the licensee's own internal regulator. The facility at that time was found to be in a poor condition and a number of poor working practices were then in evidence. During this intervention I revisited the facility to observe that whilst there remain some housekeeping issues which the licensee still needs to address, the key issues from the last inspection had been satisfactorily progressed by the licensee.
Overall from the inspections I conducted I am satisfied that the licensee's performance was adequate in the areas I studied.