British Nuclear Fuels has posted pre-tax losses of over £200 million sterling because of poor performances at the Magnox power stations and its showcase THORP reprocessing plant.
The results prompted environmental group Friends of the Earth to call for the National Audit Office (NAO) to investigate the running of the nuclear group.
"BNFL is losing money like a Soviet steel works", said Mr Mark Johnston in a statement criticising the British government for failing to supervise BNFL on behalf of taxpayers.
The audit office last investigated government supervision of BNFL in 1989.
BNFL chief executive Mr Norman Askew said the results reflected the closure of the Wylfa power station for most of the year and difficulties at a downstream treatment plant at its Sellafield site which hurt operations at the THORP reprocessing plant.
But Mr Askew said he was encouraged that nuclear power might see something of a revival.
In May US President Mr George W Bush announced plans to increase nuclear power production and this week Britain declared it was undertaking a review of the country's energy policy including looking at nuclear power.
"We have got the best portfolio of new reactor designs (via subsidiary Westinghouse) anywhere in the world. If demand for new nuclear build comes, we are ready to go." Mr Askew said.
He added the group was eagerly awaiting a British government decision on whether it could start up its £482 million Sellafield MOX Plant (SMP) built four years ago to make reactor fuel from combination of uranium and plutonium oxides.
The Labour government is set to make a decision sometime this summer after it considers a report by independent consultants on MOX's economic viability.