Highland MP Paul Monaghan is calling on the prime minister to be “honest and open” about a plan to ship enriched uranium from Dounreay to the United States.
According to reports, the UK Government is preparing to transport 5kg of weapons-grade material to the US government’s nuclear power complex at Savannah River in South Carolina.
It is understood to have been taken to the north of Scotland facility after being airlifted out of the former Soviet republic of Georgia in 1998.
The SNP’s Mr Monaghan said David Cameron’s “denials and unanswered questions” were “a cause for alarm” in his Caithness, Sutherland and Easter Ross consistency.
But his claims were rubbished as “unnecessary scaremongering” by a senior government source.
SNP Westminster leader Angus Robertson raised concerns about the transport of “dangerous” nuclear material on public roads in Caithness at Prime Minister’s Questions earlier this month when George Osborne was standing in.
Mr Monaghan said this had been followed up with a letter from Mr Cameron denying there were any plans to move weapons-grade uranium – intended for use in nuclear missiles – from Dounreay.
Yesterday he added: “I am again calling on the prime minister for immediate openness and honesty surrounding the transportation of any exotic fissile material by whatever transportation method used.
“The people who live within my constituency deserve to know what is taking place in in the waters and roads in their own back garden.
“The infrastructure within my constituency is totally inadequate to guarantee complete safe transportation of materials of this nature.”
He also said that as a civil facility, Dounreay was not built to store the “raw materials for nuclear weapons”.
A second government source confirmed material had been moved from Dounreay to the US in the past, but insisted the material would not end up in missiles.
They told the Press and Journal no nuclear nation is allowed to transport nuclear material from one place to another for weapons.
A Downing Street spokesman said: “The decommissioning of Dounreay has been planned since 2013 and removal of nuclear material is, of course, necessary to achieve this.
“There has been, and continues to be, regular engagement between the local communities around Dounreay, the site operators, the Nuclear Decommissioning Authority (NDA) and the Scottish Government.
“The prime minister wrote to Mr Robertson earlier in the month explaining all of this.”
An NDA spokesman said: “Any movement of material is subject to stringent regulations and can only take place if it complies with legislation and is authorised by the independent regulator.”