A vote is being held on whether to go ahead with a search for a site to store high level nuclear waste.
Further investigations into building a £12bn underground nuclear waste store in Cumbria have been rejected.
Executive members of Cumbria County and one of either Allerdale or Copeland Borough Councils must agree if "Stage 4" of the process is to go ahead.
Cumbria County Council vetoed a move to "Stage 4" of the search for a site for the radioactive waste facility.
This would include detailed geological investigations and discussions over the social and economic implications.
The stage included detailed geological investigations and discussions over the social and economic implications.
Even if the £12bn underground repository is approved, construction is not expected to begin before 2025.
The county council ruled out Allerdale Borough, although that council was due to vote on the issue. Copeland Borough Council voted in favour the plans.
Cumbria is the only area still considering such a facility.
The council voted seven to three against continuing with the plans.
Nuclear power is seen as an essential part of the government's environmental plan to tackle climate change.
At the meeting Cumbria council leader Eddie Martin said it was the "most courageous and pivotal decision" the council could make.
The government appears willing to offer firms sufficient cash to build one or more new nuclear stations.
The missing piece of the jigsaw is the other long-standing environmental question - where to put the UK's nuclear waste?
Experts generally agree that deep burial is the best long-term solution.
But Cumbria is the only area in the UK that has volunteered to consider hosting an underground store.
The region already faces a threat from above-ground waste stored in decaying holders which MPs said presented "intolerable risks" to people and the environment.
But there are still doubts about whether the geology will present a suitable underground alternative.
If an appropriate site can be found, experts say the risks will be greatly reduced. But the tourists so vital for the region may not see it that way.
Dungeness in Kent, which had initially shown interest, withdrew at the end of 2012 in the face of opposition from residents.
Currently, radioactive waste is stored above ground in various "long-term temporary" sites around the UK, mostly at Sellafield in Cumbria.
Unions representing workers in the nuclear industry have expressed support for studies to go ahead.
Garry Graham, deputy general secretary of Prospect, said: "Not only does the vote have vast implications for the economic wealth of West Cumbria, which relies so heavily on the nuclear industry for jobs and growth, it potentially casts a shadow over any nuclear renaissance in the UK."
However, the Lake District National Park Authority is concerned that an underground nuclear waste repository would impact negatively upon the tourist industry, which is currently worth an estimated £2bn annually.
The Cumbria County Council and Copeland Borough Council meetings began at 10:00 GMT, while Allerdale Borough Council's meeting is set to begin at 15:00.
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Are you in Cumbria? What do you think of the nuclear waste project? Please send us your comments using the form below.
