Protesters who chained themselves to the gates of Hartlepool nuclear power station have been arrested.
The protest did not halt work at the plant
Police said 20 green activists from Reclaim Power arrived at the British Energy-owned complex early on Tuesday.
Police said six chained themselves to gates at the front and rear of the advanced gas reactor and had to be cut free by a Ministry of Defence team.
The group, arrested for trespassing, is angry at the government's plans to build more nuclear power stations.
The protestors, who chained themselves together using pipes and metal plates, were cut free on Tuesday evening and arrested on suspicion of aggravated trespass.
All 20 have been taken to separate police stations for questioning.
Supt Steve Ashman of Cleveland Police said all of the protestors had been given a chance to hold a lawful protest, but had blocked a vital access road to the plant.
Reclaim Power claims to be a network of green campaigners made up from other environmental organisations, including Greenpeace and the Camp for Climate Action.
Darren Locke of Reclaim Power said: "Nuclear power is not a solution to climate change.
"While it may be true that nuclear power results in fewer greenhouse gas emissions than burning fossil fuels, nuclear power produces deadly waste which remains radioactive for thousands of years."
Power generation began at Hartlepool in 1983. It is due to be decommissioned in 2014.
Earlier this year the government said nuclear power could make a "significant contribution" to Britain's future energy needs.