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British Ministry of Defense (MoD) has decided to refuel the nuclear reactor in one of the country's four ballistic missile submarines at a cost of about 120 million pounds (200 million U.S. dollars), British Defense Secretary Philip Hammond said Thursday.
The decision came after low levels of radioactivity were detected in the cooling water surrounding a prototype core that has been running at the Naval Reactor Test Establishment at Dounreay in Scotland since 2002.
The purpose of the prototype is to help MoD evaluate the performance of the reactor cores within submarines, seeking to identify in advance related issues that may arise in the lives of the operational reactor cores.
These low levels of radioactivity are a "normal product" of a nuclear reaction that takes place within the fuel, but they would not normally enter the cooling water, Hammond explained in an oral statement to the British Parliament.
The water is contained within the sealed reactor circuit, and there has been no "detectable radiation leak" from that sealed circuit, he added.
Hammond said the refueling plan is a "precautionary" measure, as there is no evidence at this stage that the problem detected with the test reactor will likely affect the operational reactors.
Based on the International Atomic Energy Agency's measurement scale for nuclear-related events, the issue detected with the test reactor has been classed as "Level 0", described as "below scale--no safety significance," according to MoD.
The refueling will be carried out within the planned maintenance period for Vanguard from late 2015 and will last for about three and a half years, Hammond said.
The maintenance is expected to have no impact on deterrent operations before Britain's fleet of new generation "successor" nuclear submarines begins to be delivered from 2028.
Britain is undertaking an ambitious upgrading of its Trident system, a sea-based nuclear weapons system that can fire ballistic missiles from submarines.
