Still not fully open since the leakage accident in April 2005, hopes to restart THORP soon have been dented by the mechanical failure earlier this week of the elevator system which feeds fuel from the plant’s feed pond into the main plant for reprocessing.
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Despite THORP re-start approval having previously been given by HSE’s Nuclear Installations Inspectorate (NII) late last year after the plant’s almost three-year accident closure, normal reprocessing has so far been impossible because of the unavailability of a downstream evaporator to deal with THORP’s liquid high level wastes. Whilst the lack of evaporative capacity remains an ongoing problem, the breakdown of the feed pond elevator on 28th January is likely to add further to the delay in getting back to full operation.
The relatively small feed pond is located between THORP’s receipt & storage ponds and the plant’s head-end where the fuel is sheared and dissolved in nitric acid. Batches of fuel for reprocessing are moved on a bogey from the feed pond via the elevator up the steep gradient into the head-end. It is understood that the bogey loaded with some fuel began the ascent on the elevator but then slipped back onto the ramp in the feed pond. With no radiological consequences yet reported, NII has been informed of the event and initial investigations are likely to be carried out remotely. THORP’s operators British Nuclear Group Sellafield Ltd (BNGSL) estimates that the breakdown is likely to keep the plant closed for several weeks.
With repairs and modifications completed to the cell involved in the 2005 leakage accident, and with NII approval to process a test batch of fuel through the head-end last year, 33 tonnes of British Energy’s AGR fuel was sheared and dissolved in the summer. The fuel caught up in this week’s elevator failure will have been part of the further 100 tonnes projected by the plant’s NDA owners to be sheared and dissolved by the end of this financial year on 31st March 2008 – an annual throughput of around 120 tonnes. Until the evaporator problems are resolved, the dissolved liquor from the test batch fuel will be held in buffer storage tanks within THORP.
With some 800 tonnes of foreign fuel still to be reprocessed in THORP, overseas customers already highly critical of the plant’s past performance will be dismayed by this latest breakdown and the further inevitable delay it will cause to the reprocessing of their fuel. The plan to complete all overseas contracts by 2010/11 – already 2 years behind at the time of the THORP’s accident closure in 2005 – has now slipped to an overall delay of at least 5 to 6 years.