Sellafield’s beleaguered Thorp nuclear reprocessing plant cost more than £110 million in lost revenues as it lay idle last year.

Unions have warned that the losses and Thorp’s continued inaction could raise concerns over the plant’s future.

The Nuclear Decommissioning Authority, the nuclear clean-up watchdog, revealed that the closure of Thorp led to a sales shortfall of £112 million. The drop in revenues was one of the main factors that forced the Government to increase its support for the remainder of the state-owned nuclear operations late last year.

Thorp, the UK’s main nuclear reprocessor, was out of action for two years as engineers dealt with a spate of technical difficulties. Last month the plant, which handles waste for Japanese and European nuclear generators as well as British Energy, began limited small-scale reprocessing but there is no target for a full start-up.

Thorp is now struggling with difficulties with the evaporator system. This also affects Sellafield’s separate Magnox fuel reprocessing facility, which handles waste from Britain’s old generation of nuclear reactors. It had been intended that Thorp would re-open properly this summer.

Thorp is the key part of the Sellafield complex, which is being sold off as part of the Government’s privatisation of its remaining nuclear assets. Four consortiums are bidding to run the site, which should be capable of generating good returns from its overseas customers.

A spokesman for Sellafield Ltd said work was continuing to bring Thorp fully back on stream.

Mike Graham, national officer for the engineering union Prospect, said: “There need to be urgent decisions about Thorp. We can’t afford to carry on with losses such as these.”

Thorp’s continued problems are likely to push down the price the bidders for Sellafield are prepared to pay. Bidding for the work are CH2M Hill International Nuclear Services, the US group; Fluor, working with Toshiba; SBB Nuclear, a group including the UK companies Serco and Bechtel; and Washington Group International, working with Amec and Ariva.

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