Thorp nuclear fuel reprocessing plant

The Thermal Oxide Reprocessing Plant, or THORP, is a nuclear fuel reprocessing plant at Sellafield in Cumbria, England. THORP is owned by the Nuclear Decommissioning Authority and operated by Sellafield Ltd (which is the site licensee company). Spent nuclear fuel from nuclear reactors is reprocessed to separate the 96% uranium and the 1% plutonium, which can be reused in mixed oxide fuel, from the 3% radioactive wastes, which are treated and stored at the plant. The uranium is then made available for customers to be manufactured into new fuel.

THORP is due to close in 2018 once all existing reprocessing contracts have been fulfilled.

Construction of THORP started in the 1970s, and was completed in 1994. The plant went into operation in August 1997.

Between 1977 and 1978 an inquiry was held into an application by British Nuclear Fuels plc for outline planning permission to build a new plant to reprocess irradiated oxide nuclear fuel from both UK and foreign reactors. The inquiry was to answer three questions: "1. Should oxide fuel from United Kingdom reactors be reprocessed in this country at all; whether at Windscale or elsewhere? 2. If yes, should such reprocessing be carried on at Windscale? 3. If yes, should the reprocessing plant be about double the estimated site required to handle United Kingdom oxide fuels and be used as to the spare capacity, for reprocessing foreign fuels?". The result of the inquiry was that the new plant, the Thermal Oxide Reprocessing Plant, was given the go-ahead in 1978, although it was not completed until the 1990s at a cost of £1.8 billion.

In 1998/99, the plant faced severe economic difficulties when it failed to reach its reprocessing targets. Shut-downs for six months in the first half of 1998 and for several further months from December 1998, due to leakages, resulted in a failure to achieve the target of reprocessing 900 tonnes of fuel over that period. Most of the reprocessing contracts were with Germany and Japan.

The chemical flowsheet for THORP is designed to add less non-volatile matter to the first cycle PUREX raffinate, one way in which this is done is by avoiding the use of ferrous compounds as plutonium reducing agents. In this plant the reduction is done using either hydrazine or HAN (hydroxylamine nitrate). The plant releases gaseous emissions of krypton-85, a radioactive beta-emitter with a half-life of 10.7 years. The Radiological Protection Institute of Ireland (RPII) commenced 24-hour atmospheric monitoring for krypton-85 in 1993, prior to the plant's commissioning.

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