Opposition politicians have called for a parliamentary inquiry into the handling of a radiation leak at a nuclear test reactor.
Public confidence has been damaged by the incident at the Vulcan Naval Reactor Test Establishment in Dounreay, Caithness, according to shadow defence secretary Vernon Coaker and shadow Scottish secretary Margaret Curran.
UK Defence Secretary Philip Hammond revealed details of a small internal leak of radiation on Thursday as he announced that the nuclear submarine HMS Vanguard is to have its reactor refuelled at a cost of £120 million.
Mr Coaker and Ms Curran said there were "significant questions" about the handling of the incident, particularly the two-year delay in making it public.
Replacing Britain's nuclear deterrent has proved a flashpoint for the Coalition with Liberal Democrats opposed to "like for like" replacement and Conservatives committed to a full renewal of the UK's fleet of four Vanguard-class submarines by 2028.
Liberal Democrat Defence Minister Nick Harvey has been conducting a review of possible cheaper alternatives.
The first of the four Vanguards had been due to leave service in 2022, but the Government extended the vessels' lives as part of the 2010 Defence and Security Review.
Final decisions about ordering replacements do not have to be taken until 2016, after the next general election.