The UK's nuclear waste clean-up programme could cost more than £70bn, according to the Nuclear Decommissioning Authority (NDA).
The cost of cleaning up existing waste is higher than previously thought
The authority's previous estimate of the cost was £56bn.
The news came as the government backed British Nuclear Fuels' (BNFL) plan to sell its specialist nuclear clean-up business British Nuclear Group (BNG).
The sale of BNG was a "positive strategic move", said BNFL's chief executive Michael Parker.
Trade and Industry Secretary Alan Johnson said he believed a competitive sale was in the best commercial interest for BNFL.
"By bringing in external expertise more quickly, it also contributes to improved clean-up performance for the NDA and is therefore good for the taxpayer," Mr Johnson said.
NDA chairman, Sir Anthony Cleaver, said the cost for the nuclear clean-up itself - including decommissioning, the clean-up of existing waste and the running of existing operations until their planned closure dates - was estimated to be £62.7bn.
SITES FOR DECOMMISSION
Hinkley Point A
Additional costs linked to contaminated land would drive up the total to about £72bn.
Much of the land contamination was "chemical, not nuclear, but it is a cost nonetheless", Sir Anthony said.
Some of the operations the NDA is committed to run, such as the Mox and Thorp fuel reprocessing plants at Sellafield and some waste storage facilities, generate an income which the NDA anticipates could total £14.3bn.
This income could cancel out the running costs of its commercial operations, thus reducing the overall decommissioning and clean-up cost to about £56bn, an NDA spokesman explained.
However, whereas the cost of running NDA's commercial operations is fixed, the income they generate fluctuate in line with volatile energy markets.
Moreover, the Thorp facility at Sellafield has been closed for a year following a leak last April. Such unpredictable occurrences threaten to disrupt NDA's revenue stream.
Private sector rivalry
Until now, the bulk of Britain's nuclear waste has been stored above ground at 37 sites across the UK.
When measured by volume, 65% of Britain's total waste mountain is stored at Sellafield, which is owned by the NDA but operated by BNG.
Finding a long-term solution to dealing with Britain's existing nuclear waste is considered essential before any decision can be made about building new nuclear power plants in the UK.
Now the Government has approved the NDA's plans for the decommissioning and clean-up of its civil nuclear sites.
Decommissioning will be fast-tracked where possible in its strategy of making the reduction of high hazards a "key focus."
"We are confident that in light of what we know today, our approved Strategy provides the best approach - in terms of safety, cost efficiency and sustainability - to tackle the UK's historic 60-year nuclear legacy," said the NDA's chief executive Dr Ian Roxburgh.
The sale of BNG has met with much opposition from workers.
"Our union is opposed to the sale of the British Nuclear Group in principle," said Amicus national officer Dougie Rooney.
"But we are also concerned that it could compromise the government's stated objectives of decommissioning civil nuclear sites in the UK at a reduced cost to the taxpayer and a reduced timescale while maintaining safety standards."
The GMB union was equally critical.
"We consider that the proposal to privatise British Nuclear Group will set up a Railtrack in the nuclear industry," said Gary Smith, national officer at the GMB.
"Like Railtrack it will be dependent on public money, the private sector managers will look out for number one, and any corners cut could lead to a catastrophic mistake."
Environmentalists were also angry.
"Every time the costs of cleaning up nuclear sites are looked at, the cost for the taxpayer spirals," said Greenpeace nuclear campaigner Jean McSorley.
"It's just one more reason why it would be insane to countenance building more nuclear power plants across Britain."