Controversial £30bn plans for a Severn estuary barrage tidal energy project have been scrapped.
Supporters had claimed the 10-mile (16km) dam stretching from Somerset to south Wales would produce up to 5% of the UK's energy.
Energy Secretary Chris Huhne said a study had found there was "no strategic case" for the scheme.
Mr Huhne also announced eight potential sites for building new nuclear power stations by 2025.
They are at Bradwell in Essex; Hartlepool, Tees; Heysham, Lancashire; Hinkley Point, Somerset; Oldbury, Gloucestershire; Sellafield, Cumbria; Sizewell, Suffolk and Wylfa, in Anglesey.
Dungeness, in Kent, and Braystones and Kirksanton, in Cumbria, were rejected.
The Severn barrage had been intended to run from Weston-super-Mare to Cardiff.
Conservative MP for the Forest of Dean Mark Harper said the feasibility study, carried out by the Department of Energy and Climate Change, showed it was right to look into the detail of the costs and benefits before proceeding.
'Die another death'
"However, it was expensive and I was not convinced it was the right way forward. Other low carbon options, like new nuclear power stations, seemed to make more sense. I am pleased that the Energy Secretary has also reached this conclusion."
A statement from Gloucester County Council said while it was disappointing that the barrage project had been axed, in the current economic climate it was "totally understandable".
But a spokesman for the RSPB, which was worried about the effect the development would have on bird habitats, said it was pleased to see the barrage proposal "die another death".
"The Severn is one of the tidal energy hotspots of the world and its future has to be one of a more sustainable technology - one that taxpayers, engineers and environmentalists can all celebrate."
The Severn estuary has the second-largest tidal range in the world with 42ft (12.8m) tides.
The feasibility report found it would be difficult to attract private investment and the project represented "high risk".
Mr Huhne did not rule out the possibility of the barrage as a longer term option in the future, if market conditions improved.
'Only real shows'
He said: "The study clearly shows that there is no strategic case at this time for public funding of a scheme to generate energy in the Severn estuary.
"Other low carbon options represent a better deal for taxpayers and consumers.
"However, with a rich natural marine energy resource, world leading tidal energy companies and universities, and the creation of the innovative Wave Hub facility, the area can play a key role in supporting the UK's renewable energy future."
Gary Smith, from the GMB union, which represents many power station workers, welcomed news of investment in the nuclear industry.
He said: "These are very big investments and the financing has to be properly under-pinned. Carbon capture and storage and nuclear are the only real shows in town in terms of supplying the base load for electricity in a carbon-free way.
"Other sources have a role but they cannot supply the base load of electricity the UK needs," he added.