Union leaders are calling for steps to be taken to protect the jobs of staff at Sellafield in the run up to the plant's decommissioning.
The Nuclear Decommissioning Authority takes over in April
The Cumbrian nuclear reprocessing plant is among a number of UK nuclear sites due to be decommissioned.
Union Amicus says permanent staff need to be retrained to carry out the decommissioning work and it will oppose the outsourcing of any core work.
Amicus general secretary Derek Simpson is visiting Sellafield on Wednesday.
The Nuclear Decommissioning Authority (NDA) will assume ownership of Sellafield in April next year and decommissioning will start.
Amicus says that no new jobs are likely to be created at the site during decommissioning and so the focus must be on training staff to manage the process.
Mr Simpson said: "We need to maximise the number of job opportunities available through the decommissioning process by re-skilling Sellafield workers.
"Unless we start training people now, we are in danger of damaging the whole of UK manufacturing and disadvantaging Sellafield workers and the whole Cumbrian economy.
"Amicus is committed to maintaining our members' terms and conditions at Sellafield - ensuring that pay and pensions provision are not threatened by the outsourcing of work."
The union says permanent staff at the plant are likely to be cut from 12,000 now to 4,000 by 2011.
British Nuclear Fuels Ltd, which runs the Sellafield site, said: "Training our workforce to meet the challenge ahead will continue to be an important part of our plans.
"At the same time the NDA is seeking best use of the supply chain to demonstrate best value for the taxpayer."