(May 27, 2005) The leak of 83 cubic meters of dissolved nuclear fuel at Sellafield's THORP reprocessing plant could not have come at a worse time for the plant's operators British Nuclear Group (BNG). Consisting of an estimated 22 tons of dissolved fuel from a European customer and including some 160kg of plutonium, the leak occurred just days after British Nuclear Fuels (BNFL), of which BNG is one of four business groups, handed ownership of the Sellafield site and THORP to the Nuclear Decommissioning Authority (NDA) on April 1.
(628.5689) CORE - In readiness for the NDA takeover, BNFL launched BNG in 2004 as a specialist clean-up business within BNFL to achieve clean-up and decommissioning work at UK nuclear sites 'quickly, safely and cost-effectively'. It joined BNFL's other main groups Westinghouse, Nuclear Sciences & Technology Services and Spent Fuel Services.
For a contractor seeking to impress its new bosses that it is fit to hold the Sellafield contract, an accident of this magnitude - projected to close THORP for 'months' - is not the most impressive start, especially at a plant already several years behind with its orders. Officially classified as an INES Level 3 Serious Incident, BNG estimates radioactivity levels in the liquor to be around 100,000 TBq (Chernobyl released 89,000 TBq) though some believe this to be a highly conservative figure. At Level 3, the leak is THORP's worst yet and is the first to be recorded at Sellafield since 1992 when the older magnox reprocessing plant sprung a similar but smaller leak.
Opened in 1994, THORP should have reprocessed around 7000 tons of spent fuel by March 2004. Two-thirds of this business was contracted with overseas customers. However, a litany of in-plant accidents and incidents, and problems in down-stream processes such as vitrifying THORP's liquid High Level Wastes, means the original target is still some 1500 tons short of being achieved. Now in its 12th year - and facing further delays because of the accident - THORP's status as an "asset" on the NDA's books looks decidedly suspect.
The cause of the leak is given as fractured (clean break) pipe in THORP's Feed Clarification Cell at a point where the pipework feeds into one of two accountancy tanks. During normal transfer through this cell to THORP's Chemical Separation plant, the dissolved liquor would be centrifuged to remove any remaining solids and then fed into the accountancy tank where the liquor is weighed and its fissile component accounted. First detected on 18th April when operators realized that material already sheared and dissolved had not reached the accountancy tank, in cell cameras pinpointed the source and extent of the leak. How long the pipe had been leaking remains one of the issues under investigation by a BNG Board of Investigation and by the Nuclear Installations Inspectorate (NII). The NII will also be looking at the frequency of equipment checks by BNG prior to the accident and whether there may have been breaches of licensing conditions.
The first stage of THORP's recovery involves pumping the liquor from the floor into a separate tank in the Feed Clarification cell from which it will be fed back into the system probably via the centrifuge. With a possible start this week, BNG has estimated that pumping will take four weeks. An additional complication is the discovery that as the liquor leaked into the cell, it partially dissolved some steel framework alongside the accountancy tank. Whether this framework, used occasionally to calibrate the accountancy tank itself, can be repaired is currently unknown as are the implications of the presence of dissolved steel in the liquor on the cell floor.
In parallel with the pumping program, the second recovery stage will entail an assessment of how and if, with no human entry into the highly radioactive cell, the fractured pipe can be repaired. If it cannot be repaired, further decisions must be made on the viability of restarting THORP using only the second accountancy tank - and what reliance can safely be placed on the integrity of its pipework which will share an identical history to the suspect pipework involved in the accident.
These assessments and decisions are not only for engineers and safety regulators but also for the NDA who, as new owners, will want to know repair costs and timings as well as, for example, how operating on one accountancy tank would reduce future reprocessing throughput. Any closure of THORP or limits on its operations will inevitably result in loss of revenue and therefor a shortfall in NDA's money to finance Sellafield's clean-up program. Following the accident, the NDA has said that a review of THORP's future, planned for later this year, will now be brought forward. Whilst one NDA spokesman has publicly suggested that it may not be worth re-opening the plant at all, its chairman, Sir Anthony Cleaver, has pointed out that any final decision on THORP will be a matter for UK Government.
Other than its interest in the repair program, the NDA will have other major issues to consider when deciding whether THORP should continue operating until BNG's projected closure date of 2010. Most contentious of all will be the justification for reprocessing several thousand tons of British Energy's (BE) Advanced Gas Cooled reactor (AGR) fuel, which was contracted in the 1990's for THORP's 'post-baseload' period (the second ten years of operation). With no new orders and with dwindling contracts for this period from German utilities, this AGR fuel is the only business left for THORP. In 'recycling' terms, there can be no reason for reprocessing this fuel for, as BE has repeatedly pointed out, it has no use whatsoever for the uranium and plutonium that would be recovered. Further, BNG has confided to some NGO's that, once the more lucrative overseas contracts are completed, it would be uneconomic to reprocess AGR fuel on its own.
The current accident has therefore come at a defining moment for the plant, with a majority of overseas business completed and only the prospect of 'uneconomic' business to come. The relevance of this crossroads for THORP is unlikely to be missed by the NDA whose eventual recommendations - involving best use of taxpayers' money - could sway the Government into an early closure of the plant.
Source and Contact: Cumbrians Opposed to a Radioactive Environment (CORE), 98 Church St., Barrow, Cumbria LA14 2HJ, UK
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