Sellafield's ageing THORP plant flunks major foreign fuel reprocessing target

Martin Forwood

Stumbling along at half speed to its scheduled end-date of 2018, Sellafield's 'flagship' Thermal Oxide Reprocessing Plant (THORP) continues to notch up missed targets - this time the completion of all overseas reprocessing contracts by the end of 2016. Overseas customers must now wait (at least) until 2018 (the closure date for the plant itself) to see the end of what has been, for them, a less than rewarding reprocessing experience.

In early 2014, a Sellafield stakeholder meeting was told that the shearing of all remaining overseas LWR fuel - scheduled to be dealt with in roughly equal tranches over financial years 2014/15 - 2016/17 - would be completed by November 2016. Featuring high on Sellafield's 'to do' list, the 2016 projection was highlighted as a 'key activity' by the Nuclear Decommissioning Authority (NDA) in its Business Plan 2014-17, an annotation that reflected the pressure exerted by successive UK Governments - concerned by the loss of face from any failure of inter-government contract agreements - for the earliest completion of overseas reprocessing work.

By October 2015 however, Sellafied Ltd admitted to the same stakeholders that technical difficulties within THORP had prevented the reprocessing of any overseas fuel in 2015/16 and that the outstanding tonnage was now scheduled for completion by THORP's closure in 2018. As shown in the Table below, published by the UK Government's Department of Energy & Climate Change (DECC) in January 2015, the outstanding contracts amount to some 150 tonnes with German utilities dominating the list at 146 tonnes. The remnant overseas contracts are likely to be dealt with via 'virtual reprocessing', where equivalent amounts of fissile materials and waste would be allocated to each client.

Table contains data at 9 January 2015 for Sellafield THORP and Magnox fuels. Note: all overseas Magnox fuel has been reprocessed.

Providing only limited detail of the technical difficulties within THORP that has forced the new delay in completing the German contracts, Sellafield Ltd has pointed the finger at the problems associated with insoluble fuel debris (including the cladding of the fuel) which results from the initial stage of reprocessing when the spent fuel is sheared and dissolved in nitric acid. Whilst some debris is sieved out at the dissolver stage, other insoluble debris is transported within the dissolved liquor through further stages of the plant where, in the form of 'coarse fines', it causes internal scouring, pipework erosion and system blockages.

Whilst such events have caused a number of extended THORP stoppages over the years, in this case the problem lies apparently with the development of a pinhole in a decanter, which is designed to remove any remaining fuel debris from the dissolved fuel liquor prior to its further chemical separation. Given the historic experience of the zirconium alloy fuel cladding of overseas LWR fuel proving more problematic than UK AGR fuel in terms of blockage and erosion, the former has been re-scheduled in order to protect the remnant life of 21-year old THORP by providing an easier run-in to its 2018 closure date.

The fallout from the enforced re-scheduling of overseas fuel falls squarely on the unfortunate German utilities that own the 146 tonnes of LWR fuel that remain to be reprocessed, some of which was contracted for THORP's first ten year Baseload period and projected for completion by 2004. The prospect of that completion now slipping to 2018 - an overall delay of 14 years - will doubtless further infuriate the very same Baseload Customers (BLC) who, in a leaked document relating to a meeting with British Nuclear Fuels plc (BNFL) in September 2000, warned of a loss of confidence in Sellafield's technical ability that was enhanced by "BNFL's apparent inability to reprocess our fuel within the agreed baseload period". The German power stations from whom Baseload contracts had been secured for THORP included Krummel, Brokdorf, Unterweser, Grohnde, Biblis, Neckarwestheim, Gundremmingen and Lingen.

The planned closedown of THORP in November 2018 - described as a political decision unlikely to be reversed - will lead to a 4-year period of Post Operative Clean Out (POCO) of the plant. As a pre-cursor, THORP's Receipt and Storage Pond water will be caustically 'dosed' to enable the long-term storage of the estimated 5400 tonnes of AGR spent fuel that will remain un-reprocessed and pond-stored prior to disposal. Such a status has enraged Sellafield's trades unions and some local authority members who are threatening to withhold any further support for the UK's ongoing search for an underground waste dump that will contain spent fuel they consider best reprocessed.

Bringing in much needed revenue to the Nuclear Decommissioning Authority to help towards Sellafield's ever rising clean-up and decommissioning costs, completing this overseas work has long been a priority for the UK Government and Sellafield Ltd. Put in context, THORP's original order book included some xxx tonnes of LWR fuel from overseas utilities. All such contracts, plus those secured from the UK's fleet of AGR power stations, were originally scheduled for completion in 2010, a date that had to be abandoned in 2005 when THORP suffered a major leak accident (INES 3) which closed the plant for almost 2 years and reduced its future 'throughput' by around 50%.