Sellafield Ltd, the company that operates THORP (Thermal Oxide Reprocessing Plant) under contract to the Nuclear Decommissioning Authority (NDA), faces the prospect of having to close the plant for an indefinite period because of increasing problems with managing the dangerous liquid high level wastes produced by the site’s reprocessing operations. At the heart of the problem are two of the site’s three Evaporators which process the wastes and which are becoming increasingly unreliable. Whilst two new Evaporators are planned, the first is unlikely to come into service until 2013/14 at the earliest.
Evidence that drastic action may have to be taken on THORP has been mounting for Sellafield Ltd for some months. Recent behind the scenes reviews by Sellafield Ltd, in recognition of the worsening Evaporator situation, have had to assess alternative and draconian options for THORP’s future, including a moratorium on reprocessing at the plant and, as a second option, operating the plant for part of the year only.
The prospect of such scenarios arising has increased with today’s confirmation from Sellafield Ltd that one of the site’s three Evaporators has had to be shut down after a rise in radioactivity levels was discovered within one of its internal heating/cooling coils. The company is ‘working to understand the impact on Sellafield’s operational activities, including THORP’.
Responding to the announcement, CORE spokesman Martin Forwood said today “ This can only be bad news for THORP which already has a dreadful operational record. It would be kindness itself, and make the most sense, to put this white elephant out of its misery permanently”
Opened in 1994 with the assurance from its then owners British Nuclear Fuels plc (BNFL) that as Sellafield’s ‘flagship’ plant, THORP would reprocess 7000 tonnes of spent fuel in its first ten years of operation (the baseload contracts), two-thirds of the business coming from overseas customers. Today, in its sixteenth year of operation, THORP has completed just 6000 tonnes of that initial order book and is now, largely as a result of the suspect Evaporators, consigned to operating at an annual throughput rate of some 200 tonnes – less than 20% of its original design capacity of 1200 tonnes per year. There remain some 700 tonnes of overseas fuel from the original baseload contracts still to be reprocessed, a majority of it from Germany.
Sellafield operates three Evaporators A, B & C, which process liquid HLW from the site’s two reprocessing plant (Magnox and THORP) and the effluents from the Waste Vitrification Plant (WVP). THORP, by design, is configured for use with Evaporator C only, with A and B historically used to process (evaporate and condense) WVP and Magnox wases which, for safety reasons are given priority by the NII over those produced by THORP. As such, if either A or B break down and have to be taken out of service, 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 reprocessing is therefore dependent on the regular and reliable operation of A & B, a reliability conspicuous by its absence in recent years and one that has prompted not only the need for new Evaporators to be built but also, on the back of today’s announced closure of Evaporator B, with the potential to force THORP into imminent closure.
The ageing Evaporators A & B, built some fifty years ago, are each 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 within the Evaporators. Corrosion and vibration are the most significant mechanisms threatening the integrity and lifetime of the 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 high level waste sludges
Corrosion and subsequent failure of the coils has resulted in both A & B having to be taken out of service on numerous occasions in the last few years and both are now having to be operated with less than their full complement of heating/cooling coils. Heating and cooling provision for Evaporator B, for example, has been restricted for some time to its jacket and just two (of the original four) heating/cooling coils – one of which appears, from the announcement today, to have suffered sufficient further corrosion to require it to be taken out of service.
In the absence of B, THORP’s Evaporator C and Evaporator A will have to be pressed back into service (it has recently been out of action) to deal with Magnox and WVP wastes which, for safety reasons are prioritised by the Nuclear Installations Inpectorate (NII) for evaporation over wastes from THORP. Evaporator A however can only operate at a restricted rate because, in worse condition than B, it appears to have just one serviceable coil and has to rely for heating and cooling on its jacket only. Once again, THORP will be without any evaporative capacity and unable to reprocess.
Martin Forwood added “ Limping along on out of date Evaporators with less than complete cooling and heating systems cannot be safe and is wholly unacceptable. Any responsible outfit would now pull the plug on THORP, which has other problems that limit future operation, preferably for good but at least for four or five years until new Evaporators are available”.
The first of the new evaporators, Evaporator D, was expected to be operational in 2010/11. But the project, whose original cost of £90M is now understood to have doubled, has got little further than the site foundation work. Not now expected to be operational until at least 2013, the delay to the ‘politically sensitive’ project is blamed partly on the inability of the NDA to secure sufficient funding. An Evaporator E is also in the planning system with little indication of timescales. Both new Evaporators will be of similar design to Evaporator C.