Firefighters at Sellafield have voted for a series of 24 hour strikes in a dispute over pay and the grading of the role.
The GMB union said its members voted two to one to take the action.
They are due to hold talks with Sellafield bosses next week in an attempt to resolve their on-going issues, which may avert the strikes.
Members have expressed utter frustration to us at the way that the company has treated them and indeed it certainly appears that this has been taking place for many years.
Taking industrial action is a last resort to any worker and is a sign of them having no other option due to management action.
The firefighters do a vitally important job and they feel completely taken advantage of by management, relying on doing work over and above what they are paid for. It is sinful that this highly skilled group of workers have been put in this position.
The result is that they have turned out in large numbers to express their view and in so doing delivered a strong mandate for industrial action. The firefighters at Sellafield deserve better than this.
Hundreds of Sellafield contractors have returned to work following a walk-out last week.
The 1,100 contractors were angered by the state of a changing room on the nuclear site.
The Unite union now says that "it's confident" those issues can be resolved during talks this week.
Sellafield says it's will work with the union to address their concerns.
Around 1,400 contract workers at the Sellafield nuclear site in Cumbria have staged an immediate walk out.
A Unite union spokesman told ITV Border the unofficial action at Sellafield was taken first thing this morning following a meeting with the contractors at 7am.
The workers will be off site until Monday, and the strike action will cost them each around £500.
Changing rooms are at the centre of the row, with Unite claiming they are not up to standard, and that dirty towels are left for them to use after showering.
In a statement, Sellafield say they have taken measures to ensure safety at the nuclear complex.
We are aware of an industrial relations issue involving contractors at the site, and we are closely monitoring further developments.
We have taken steps to ensure that safety, security and operations at the site will be unaffected.
Former energy minister Chris Huhne has called on the government not to allow subsidies for the nuclear industry.
Since leaving Parliament, Huhne has forged a career as an energy expert.
He was commenting on the termination of a multi-billion-pound nuclear contract, due to a botched tendering process.
No subsidies for nuclear. That was the coalition government policy. It should be the policy again but the government seems to be relenting and saying 'no, maybe we should give a few subsidies', and it's opening the door to exactly a repetition of the sort of disaster that we see today.
It is genuinely the case that for example in Sellafield where there are a lot of research facilities, and which accounts for about 70% of the cost of total decommissioning, a lot of things were thrown away in the 1950s in the urgency to generate plutonium for the atom bomb programme, as well as generating electricity.
Those things weren't properly logged. We don't know what's in the silos, and therefore you need to have a really extensive investigative programme to find out what the problems are before you can clear them up.
And if you find out they are worse than you could conceivably have expected, that's going to cost more money, so that's basically what's been happening, and we've got this enormous increase in the cost of clear up.
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A huge machine has been assembled that will clean up the most hazardous building at Sellafield.
The 360-tonne machine will retrieve radioactive waste from the Magnox Swarf Storage Silo, when it's switched on.
It's an enormous step forward for us, 20 years in the making, of getting to the position where we've got the first machine that can start to retrieve waste from these silos."
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Toshiba's involvement in the Moorside nuclear project near Sellafield could be clearer today as the Japanese firm publishes its third quarter results.
The technology manufacturer said it was reviewing all nuclear business outside of Japan, raising questions over their future input.
The General Secretary of the Unite Union is visiting Sellafield today.
Len McCluskey is expected to pledge his support for workers who are involved in a dispute with the Nuclear Decommissioning Authority about their pensions.
The unions said 16,000 workers at 19 sites across the country face cuts under plans by the Nuclear Decommissioning Authority, to make savings of £660million.