The UK Ministry of Defence (MoD) has ceased operations of the naval test reactor in the Vulcan Naval Reactor Test Establishment (NRTE) at Caithness in Scotland.
The closure follows the NRTE's Shore Test Facility (STF) land-based reactor's 13-year prototyping activity to identify potential issues that could occur onboard a submarine.
UK Naval Nuclear Propulsion programme head Commodore John Corderoy said: "Much has been learnt about nuclear reactors and it was a valuable exercise to set up the shore test facility at the time that we did.
"However, the prototyping mission is now complete and so it is natural for the reactor to be shut down."
Commissioned in 1965, the NRTE has since operated five types of submarine reactor core.
UK Defence Minister Philip Dunne said: "This valuable work has been crucial in providing the MoD with a comprehensive and detailed understanding of the long term operation of nuclear reactor cores."
The STF reactor will begin post-operational activity in preparation for future decommissioning, including de-fuelling and clearance of fuel from the site.
The test reactor workforce will be re-deployed to carry out post-operational work.
Disposal of the reactors on the site and their components is expected to be carried out after 2022.
Dunne said that the ministry will reveal further updates with regard to the future of the NRTE at a later date.
Image: The land-based reactor was used as a prototype to alert potential issues that could occur on board a submarine. Photo: UK Ministry of Defence / Crown copyright.