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THORP, living on a knife-edge, to be closed for seven months

Nuclear Monitor Issue: 

Sellafield Ltd, the company that operates THORP (Thermal Oxide Reprocessing Plant) under contract to the Nuclear Decommissioning Authority (NDA), is facing yet another extended shut-down of THORP – this time for an estimated 7 months – when the only High Level Waste Evaporator configured to deal with THORP’s high level waste is taken off line for a major investigation.

The closure comes as little surprise given that Company reports and presentations over the last year have clearly anticipated the need to take action on the plant’s operational future because of increasing problems in managing the dangerous high level waste (HLW) produced not only by THORP, but also by the Magnox reprocessing plant (B205) and the effluents from the site’s Vitrification plant (WVP). 

At the heart of the problem are the site’s three HLW Evaporators A, B & C, which condense the liquid HLW from the site’s reprocessing plant and the effluents arising from the subsequent vitrification of HLW. THORP, by design, is configured for use with Evaporator C only, whilst A and B have historically been used to process WVP and Magnox wastes respectively - both the latter given priority over THORP wastes by the Nuclear Installations Inspectorate (NII) for ‘hazard reduction purposes’.  As a consequence, if either A or B break down and have to be taken out of service (as has happened in recent years), THORP’s Evaporator C is pressed into service to process Magnox or WVP wastes, leaving THORP effectively with no ‘evaporative capacity’ and therefore unable to reprocess.

THORP’s future operations at anything like a full commercial rate are therefore dependent on the regular and reliable operation of A & B. Their unreliability in recent years however has resulted in Sellafield Ltd having to place orders for 2 new Evaporators (D & E). Of similar design to C, the first of the new Evaporators is not expected to come into operation before 2014, the project currently being only at the stage of site foundation work. The original cost of BP 90 million is understood to have escalated to some BP 400 million (US$654 million, 470 million Euro)

In May 2008, in rationing the use of Evaporator C between the various facilities, the NII approved its further use for THORP - but only up to a maximum of 300 tons of oxide fuel derived HLW. Whilst this placed a limit on THORP reprocessing, it ensured that should the operation of A or B remain problematic, the prioritised Magnox and WVP wastes could at least be diverted for processing in Evaporator C if needs be.

Against this background of uncertainty over the reliability of Evaporators, Sellafield Ltd’s recent reports and presentations have assessed a number of possible options for THORP’s future - one being a moratorium on reprocessing at the plant and another being to operate THORP for part of the year only – with its workforce redeployed to other work on site. The prospect of such options becoming a reality came a step closer on the May 18 this year when Sellafield Ltd announced that Evaporator B had been shut down following the discovery of a rise in radioactivity levels in one of its internal heating/cooling coils.

Though the closure of B for inspection was relatively short lived, Sellafield Ltd was forced to refute opposition claims that THORP faced imminent closure, and to assure its workforce that, despite the problem with Evaporator B, there ‘was no danger of any plant closures’

In early June the claim of no plant closures was however thrown into disarray when confirmation was given to CORE, at a meeting with the NDA, Sellafield Ltd and Sellafield’s new parent body organisation Nuclear Management Partners (NMP), that Evaporator C was shortly to be taken out of service for a thorough investigation.  As Evaporator C is the only Evaporator configured to process THORP HLW, THORP would have to close down for 7 months - the projected duration of the Evaporator investigation. This would include not only the physical investigation itself (thickness measurement of internal cooling coils), but also the subsequent evaluation of the data from the investigation, the making of a new Safety Case for the Evaporator, and gaining approval from the Nuclear Installations Inspectorate (NII) for future use of the Evaporator for THORP reprocessing.

The prospect of a further 7-month closure of THORP, following the large number of unplanned ‘outages’ that have blighted the plant’s operational life, will do little to calm the increasing concerns of its reprocessing customers. Already known to be highly critical of Sellafield’s inability to operate THORP properly, overseas customers must now reconcile themselves to having to wait even longer for their contracts to be completed – perhaps 13 or more years late.

When THORP opened in 1994, its contracted customers had been assured by the then owners British Nuclear Fuels plc (BNFL) that, as Sellafield’s ‘flagship’ plant, THORP would reprocess 7000 tons of spent fuel in its first ten years of operation (the base load contracts). At the end of that 10-year base load period, THORP had struggled to complete 5000 tons of that order book.

Originally scheduled to close ‘with all contracts completed’ around 2010/11, the closure date had to be put back to around 2016 when, with a total 5729 tonnes reprocessed, THORP was closed down in April 2005 following the major accident (INES Level 3) when 83,000 litres of dissolved spent fuel leaked undetected from a fractured pipe in THORP’s Feed Clarification Cell. Re-opened in 2007, and still with contracts for 800 tons of overseas fuel and 2000-3000 tons of UK AGR fuel to complete, THORP has reprocessed a further 300 tons to date, including 50 tons of overseas fuel (Dutch and Swiss), bringing the overall total reprocessed since 1994 to 6000 tons.

The throughput target for the current financial year 2009/10 – the plant’s 16th year of operation - is just 200 tons, 17% of its original design throughput of 1200 tons per year, and a rate previously described to CORE by BNFL as being commercially uneconomic for THORP. As a result of the imminent 7-month closure for Evaporator C investigation, THORP is now projected to close (with all contracts completed) in 2017, though any combination of further Evaporator failures, delays to new Evaporators or any other unexpected technical failures within THORP itself, could see reprocessing operations continuing to 2020 or beyond.

The NII’s current 300-ton limit for THORP’s use of Evaporator C is expected to be reached at some point in July this year. Once reached, and with the Evaporator taken out of service and THORP closed, the burden of processing Sellafield’s Magnox and WVP wastes will fall entirely on Evaporator B which only came back on line in July 2008 after a 43-month outage for repair. Evaporator A will be kept on stand-by.

Built some fifty years ago, A & B are fitted with a cooling/heating jacket around the base and sides of the evaporator and four internal coils, which can be used alternately for heating and cooling the HLW under process. By comparison, Evaporator C was commissioned in 1990 and has 6 internal coils. Corrosion and vibration pose the greatest threat to the integrity and lifetime of these evaporators, particularly the coils and stainless steel base of the evaporators which are subject to high temperatures and hot-spots within the bottom layer of the waste sludge’s.

Failure of the coils through corrosion has resulted in A & B being forced out of service on numerous occasions in the last few years and both now have to be operated with less than their full complement of heating/cooling coils. Heating and cooling provision for Evaporator B, for example, is restricted to its jacket and just two (of the original four) heating/cooling coils. In its Quarterly report on Sellafield (July to September 2008) the NII considered the operational life of B could be quite considerable ‘provided that waterside corrosion does not cause premature failure of the remaining two heating/cooling coils’.

For its part,  Evaporator A, with its jacket and just one serviceable coil, is kept on stand-by ‘as a contingency’ to deal with the wastes from WVP which have a lesser heat loading than those from reprocessing and are therefore less demanding on the Evaporators.

It is ironic that as the worldwide economic downturn forces household-name businesses into liquidation across the UK, reprocessing at THORP - arguably the UK’s largest white-elephant of all – should continue to get the backing of the UK Government and the plant’s owners the NDA despite its woeful performance and its increasingly poor commercial prospects. It apparently owes its survival, not on any merit as a spent fuel management option, but solely because of the revenues it continues to bring in from the now disgruntled overseas customers who signed up with THORP decades ago. The NDA, funded by the taxpayer, uses the revenues to offset some of its spiralling clean-up and decommissioning costs at Sellafield and other UK sites.

Whilst Sellafield Ltd will be keeping its fingers crossed that the site’s Evaporator problems can be overcome, it will also be working hard to understand and improve the weakness in associated facilities that similarly threaten THORP’s future. One such is the continuing underperformance of WVP whose ability to deal with the HLW from reprocessing is essential in reducing the overall stocks of HLW at Sellafield (currently just under 1000 cubic meters) as required by the NII’s 2001 Specification, to a buffer stock of 200 cubic meters by 2015. Then there is the condition of the storage tanks in which the HLW is stored prior to vitrification. Having been subject of particular NII concern over recent years because of corrosion problems, plans are now being drawn up to build new tanks, though their installation and operation is not envisaged for at least ten years.  

Whilst THORP is owned by the NDA, its operators Sellafield Ltd now come under the management of Sellafield’s new Parent Body Organisation (PBO) appointed late last year by the NDA. The PBO – Nuclear Management Partners Ltd (NMP) is a consortium of the US Washington International Holdings Ltd., AMEC and AREVA. NMP will hold shares in Sellafield for the next 17 years under a contract estimated at some BP 22 billion (US$ 36 billion, 26 billion Euro). As relative newcomers to Sellafield, NMP’s view on the future of THORP and reprocessing remains unknown.

Source and contact: Cumbrians Opposed to a Radioactive Environment (CORE). Dry Hall, Broughton Mills, Broughton-In-Furness, Cumbria, LA20 6AZ England.

Tel/Fax: +44 1229 716523