The Government will have to look for another site to bury nuclear waste after a council in the Lake District rejected any plans to create one in its area.
Leaders of Cumbria County Council voted by 7-3 against studying the possibility of having the £12 billion facility in the region.
Ministers said the decision was disappointing, while unions representing nuclear workers described the move as "short-sighted."
But there were huge cheers from environmental campaigners outside the council chamber in Carlisle when the decision was announced, and Greenpeace said it was now clear that "dumping" waste in uncertain geology near one of the country's most pristine national parks was not a solution.
The county council vote over-rides decisions on the waste site taken by borough authorities in the area.
Earlier, leaders of Copeland borough council voted 6-1 in favour of moving to the next stage in the search for a site to bury radioactive waste.
But members of Cumbria's cabinet disagreed. However they urged the Government to invest in improvements to the existing surface storage facilities at the Sellafield site, so that there was a more "robust" surface storage arrangement in the decades to come while a permanent solution for the country's higher-activity radioactive waste was found.
The decision effectively ends the county council's four-year formal involvement in the managing radioactive waste safely (MRWS) process, and puts an end to the "doubts and concerns" of many local people, said the authority.
Cabinet members made it clear at the meeting that it had been a highly contentious issue which had polarised opinions. Council leader Eddie Martin (Conservative) said: "Cabinet believes there is sufficient doubt around the suitability of West Cumbria's geology to put an end now to the uncertainty and worry this is causing for our communities."
Copeland Council leader Elaine Woodburn said it was not clear whether the borough could go ahead without Cumbria's approval. Asked if Copeland could "go it alone", she told BBC Radio 4's PM programme: "I don't know. Our priority was for Copeland to make its decision today. There's a problem that needs to be resolved. We'll have to have that discussion with the Government." She added: "It's too important to say 'This is the end' or 'We are going to do this or that'. It's too important - it needs us to take time to take a step back then talk to Government to see what is the next step."