Police made seven arrests during a mass trespass at the site of the proposed Hinkley C nuclear power station as determined campaigners dodged security staff and police to scale barbed wire-topped fencing.
More than 50 people from an alliance of anti-nuclear organisations were determined to breach the barrier to plant symbolic wildflower seeds on land they believe is being desecrated.
The protest started before dawn yesterday.
Hinkley Point is the proposed site of the first of the new generation of nuclear power plants which the Government and developer EDF Energy say are necessary to provide a mix of low carbon energy for Britain's future needs.
But campaigners say nuclear is too dangerous and want the land, which is still green fields, returned to "the people".
Dozens fanned out around the five-mile long fence while others held banners and placards outside the main security gate. A 14-foot banner reading, "Nuclear disaster zone. Boycott EDF" was hung across the gate.
One woman campaigner held a candlelit vigil.
By 11am the protesters had thrown 577 seed balls over the fence, representing the number of days since the Fukushima nuclear disaster in Japan.
Camilla Berens, spokesman for the Stop New Nuclear Alliance, said: "This is a major victory for the anti-nuclear movement. Because the government has refused to listen to us we have been forced to raise the game.
"We have successfully blockaded the main entrance to Hinkley Point on two occasions in the last year and now we have accomplished a mass trespass.
"Our message today is that we will continue to raise the game with peaceful protest until our voice in heard."
It is understood that some of the arrests were on suspicion of causing criminal damage.
Nigel Cann, C Site Construction Director for EDF said: "We are disappointed that a small minority of those who have travelled here today have chosen to ignore the arrangements made to facilitate a peaceful and lawful protest.
"There is an obvious difference in the security arrangements that are appropriate and proportionate for what is essentially a large field and those at an operational nuclear site.
"We have been able to carry out business as usual on the C site and to bring in workers and equipment needed for the maintenance programme at the B station.
"Nuclear power is a key part of the low carbon future of the UK and Somerset has the opportunity to lead the way."