TONNES of radioactive metal from a nuclear submarine reactor is secretly being cut up in the Westcountry, the Western Morning News can exclusively reveal.

A massive section of the reactor from HMS Vanguard – which was refitted and refuelled at Devonport between 2002 and 2004 – is being dismantled at the dockyard in Plymouth.

Royal Navy sources told the WMN it was first time a submarine reactor had been cut up in the UK.

Campaigners against the storage of nuclear waste at the naval base said they knew nothing of the scheme and accused the Ministry of Defence (MoD) of ignoring public opposition to reactor disposal work in the city. They fear it is a precursor to the reactors aboard seven redundant submarines stored in the naval yard being cut up at Devonport.

The MoD denied it was paving the way for further disposal work while the nuclear regulator at the Environment Agency insisted that the work was safe.

Ian Avent, of the Campaign Against Nuclear Storage and Radiation (Cansar), said: "This is the first phase in Plymouth becoming a nuclear scrapyard. The Ministry of Defence are going to use this project to justify doing all the other submarines here.

"What makes it worse is that they are doing it behind our backs."

Two Vanguard-class nuclear-powered submarines – HMS Vanguard and HMS Victorious – have already been refuelled at Devonport.

Work on the third, HMS Vigilant, is currently under way. The last of the four ballistic submarines which provide the UK's strategic nuclear deterrent – HMS Vengeance – is expected in Plymouth as soon as that project is finished.

Cutting-up work on one of the reactor heads – a domed, circular piece of high-grade steel which measures 9ft across and is 3ft thick – began nearly two weeks' ago.

The project has been sanctioned by the Environment Agency, one of the Government regulators for nuclear work. Five years ago, the public emphatically rejected any plans to manage or store nuclear waste at Devonport after consultation on the MoD's controversial Interim Storage of Laid Up Submarines (ISOLUS) project.

The project has now restarted after recommendations by the Committee on Radioactive Waste Management (CoRWM) in 2006 that the waste from Britain's nuclear reactors should be dealt with through deep burial.

Mr Avent said the secret project at the yard "made a mockery" of the past consultation and the current ISOLUS scheme, which was now being led by the MoD.

"Quite clearly, the MoD are saying one thing to the public and going through the motions of being open and transparent while pursuing their own agenda behind closed doors," he added.

There are seven submarines awaiting disposal in Plymouth, each with more than 160 tonnes of intermediate and low-level waste on board.

Independent nuclear consultant John Large said it appeared the entire reactor head, estimated to weigh 28 tonnes, had been irradiated rather than being contaminated with small amounts of radioactive debris. He said it represented around a sixth of the total reactor.

Mr Large said alloys used in modern steel manufacture meant the metal could have a half-life of around 5,000 years. He said the huge reactor head had to be cut up to fit containers approved for storage as low-level radioactive waste.

In the past, low-level waste handled by Devonport has been transported to Drigg, in Cumbria, for storage.

Mr Large, who advised the government of Gibraltar when repairs were being carried out on the reactor aboard HMS Tireless, said the latest project was "beginning to look like ISOLUS".

An MoD spokesman said the reactor "closure heads" were not being replaced because of "any suspected or discovered defect". He stressed that the project "is not related to ISOLUS".

"The reactor pressure vessel closure heads on all four Vanguard submarines has been or will be replaced as part of each refit work package," he added.

"This is not because of defects – it is to accommodate engineering improvements consistent with achieving longer periods between maintenance inspections."

He confirmed that the heads had already been replaced on HMS Vanguard and HMS Victorious "as part of a routine upgrade package".

"The radioactivity levels on the reactor pressure vessel heads categorise them as low level waste," the spokesman explained.

"As a mature nuclear licensee, Babcock is well-equipped with modern standard licensed active workshops/stores and has skilled resources familiar with low-level waste processing and disposal.

"In order to dispose of the reactor pressure vessel head, it must be cut up to prepare it for shipment off-site and long-term storage as low-level waste.

"The reactor pressure vessel head from HMS Vanguard was transported off-site where it was cut up in active workshops before being prepared for storage as low-level waste in a licensed facility.

"Waste generated on the Devonport site is removed to nationally approved disposal sites which are agreed and approved by the nuclear regulatory authorities.

"The waste arising from the disposal of a closure head will be treated in similar manner and in accordance with the Devonport site licence conditions.

"The works are not being performed as part of any submarine disposal initiative. However, any low-level waste-processing experience will serve to positively inform and clarify ongoing technical programmes."