Building work, costing £1bn, at a weapons research base and the creation of hundreds of new jobs have sparked claims of new nuclear developments.
AWE is the headquarters of Britain's nuclear development programme
Jobs have been created to work with new computer technology at the site.
Greenpeace said the international Nuclear Non-proliferation Treaty is being contravened at the Atomic Weapons Establishment (AWE) in Aldermaston.
But a Ministry of Defence spokesman said Trident nuclear missiles are not being replaced at the Berkshire base.
Greenpeace's claims centre on a video clip of Aldermaston's chief scientist Dr Clive Marsh, which the organisation said is aimed at potential AWE employees on Aldermaston's website.
'New nuclear weapons'
In the clip Dr Marsh said they aim to "develop our overall warhead design and assurance capabilities, including the ability to provide a new warhead lest our government should ever need it as a successor to Trident".
Blake Lee Harwood, Greenpeace campaign director, said: "The government is pretending to consult but they've already given the nod to a new nuclear weapons system costing billions of pounds."
Greenpeace claims that by developing new nuclear weaponary Article 6 of the Nuclear Non-proliferation Treaty is being broken.
This says: "Each of the Parties to the Treaty undertakes to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control."
The AWE at Aldermaston is the headquarters of Britain's nuclear development programme.
A spokesman said the MoD needed new scientists for computer modelling, laser physics and hydro modelling, with the last big recruitment being 30-40 years ago and current staff reaching retirement.
He said: "No decision has been taken to replace the Trident system. Trident will last until the 2020s."
The MoD plans to carry out computer-simulated testing in the new facilities.
"We have to keep warheads safe and reliable. Facilities are 20 to 30 years old," the spokesman added.
The new Orion laser computer-simulation facility is being built to replace the out-dated Helen facility.
Opposition to the building work had already been voiced in July, when anti-nuclear protesters attempted to disrupt development at Aldermaston.