Anti-nuclear weapons protesters at Atomic Weapons Establishment's (AWE) Burghfield site oppose the renewal or replacement of Trident.
Burghfield and AWE Aldermaston provide the warheads for the submarine-launched missile system.
The activists were held on suspicion of obstruction of a public highway.
The UK's existing four ballistic missile submarines are to be renewed from the late-2020s.
The government's final decision on whether to renew or replace the missile system, the UK's nuclear deterrent, is due in 2016.
'Pose a danger'
Some of the protesters at AWE Burghfield have come from Finland, Spain, Scotland, Argentina and Japan to take part.
Police said there were about 20 tents as part of a camp near the West Berkshire site.
Action AWE, which is co-ordinating the protest with Trident Ploughshares, said in a statement they were taking part in “non-violent direct action”.
They said nuclear weapons were “immoral, illegal under international law, dangerous to maintain and pose a danger to peace on Earth”.
Ch Insp Lindsey Finch, deputy local policing commander for Newbury, said: “We will continue to work with protesters to facilitate peaceful protest and ensure that any criminal activity is dealt with proportionately.”
A spokeswoman for the weapons site said: “AWE on-site security, the Ministry of Defence Police and Thames Valley Police are currently in attendance and will remain for the duration of any protest action.”