The race to take over the Sellafield nuclear reprocessing facility could be delayed by a legal battle over the cost of a radioactive leak.

The management of the site, which is currently undertaken by British Nuclear Group Sellafield, is being retendered as part of the break-up and privatisation of the state-owned British Nuclear Group (BNG).

A number of construction firms are considering making a bid for the reprocessing contract as a way of entering, or strengthening their positions in, the nuclear market.

However, it emerged this week that a writ has been served on BNG from German energy supplier Eon, which is attempting to bar it from recovering the costs of a leak of radioactive material at Sellafield in 2005.

The case could saddle the Sellafield site manager with higher costs for repairing and operating the plant, together open-ended legal costs. This will come as a blow to firms such as Bechtel and Serco that had expressed an interest in the running the plant.

The claim from Eon and two of its subsidiaries, Grohnde and Brokdorf, relates to the leak of 83,000 litres of radioactive fluid from a broken pipe at the Thorp plant.

In October, the Health and Safety Executive fined BNG 拢500,000 for the incident. BNG has been trying to recover some of this money, as well as other costs, from Eon, which uses the plant to reprocess its waste.

A number of firms were considering making a bid for BNG as a way of entering the nuclear market

In its writ, Eon claims the leak 鈥渉as given rise, and is likely to continue to give rise, to considerable expenditure by BNG鈥�. Eon says it has already been invoiced by BNG Sellafield for some of the costs, but says it believes BNG is not entitled to recover them because they 鈥渁re the result of, or have been increased by, BNG鈥檚 own breach of statutory duty and/or contract and/or negligence鈥�.

A source close to the case said: 鈥淏NG has indicated that it will try to recover the costs, and Eon鈥檚 writ is a protective measure against this. We are talking about sums far in excess of 拢500,000. There are costs associated with the plant being shut down, and a lot of knock-on costs. Who knows what it will amount to?鈥�

The writ is also a setback to the government, which has already released information packs to parties interested in the BNG break-up. Earlier this month, US Bechtel announced it had formed a consortium with UK support services firm Serco and US nuclear specialist BWXT to bid for the clean-up operation at Sellafield.

Amec, Atkins and energy giant Fluor are also thought to be interested in parts of BNG, and consultant EC Harris has expressed interest in the project services arm of the group.

BNG was unavailable for comment.