The cost of clearing four decades of nuclear waste at Dounreay in the Scottish Highlands has soared by £200m, after major changes were made only two years into a 10-year contract.
The engineering firm managing Dounreay, Babcock International, is understood to have warned the Nuclear Decommissioning Authority that it cannot get away with significantly altering the clean-up programme without additional costs. The contract is worth £150m a year until the 69-year-old site, where scientists experimented with plutonium and uranium, is environmentally safe, between 2022 and 2025.
Babcock is believed to have asked for the additional money in what is known as a "change order", with negotiations set to last through the summer.
A Dounreay site spokesman said the "information was as good as it could have been" when the contract was awarded, but "more enhancements to security" are needed. There are also extra transportation costs in the earlier years of the project, as the fuel on the site is now being transferred to Sellafield in Cumbria.
The news comes days after a Babcock-led consortium surprisingly won the £7bn contract to decontaminate the Magnox reactor sites, from Hunterston in Ayrshire to Dungeness in Kent.
The four consortiums that bid for the contract are preparing to appeal the decision. An NDA spokesman said that no legal challenge has been mounted "at this stage".