Errors during maintenance work resulted in a breach in the primary containment of the reactor compartment for HMS Vengeance, one of the submarines that carry the Royal Navy's Trident nuclear weapons, during refit work last year at Devonport dockyard.
The reactor's primary containment – the principal barrier preventing a release of radiation to the surrounding environment – was breached when reactor compartment salvage valves were inadvertently removed during early stage work in the refit programme. According to the Office for Nuclear Regulation (ONR), the event was initiated “through a series of misunderstandings regarding the significance of these valves”. The breach took place at a stage in the refit programme after the reactor had cooled down from operational temperatures, and the risk of a nuclear release was extremely low.
The event has been investigated by Devonport Royal Dockyard Ltd, a subsidiary of Babcock International Ltd which operates the Devonport dockyard and is responsible for delivering the Navy's submarine refit programme, and a number of recommendations have been made with the aim of preventing similar incidents in future.
The incident, which took place in November 2012, came to light when details were reported in the latest quarterly site report for the Devonport dockyard published by ONR.
HMS Vengeance is currently undergoing Long Overhaul Period (Refuel) refit in 9 Dock at Devonport dockyard. During the refit the submarine will be fitted with a new reactor core with sufficient fuel to provide power for the remainder of its operational life.
Concerns about inadequate quality of work in the Ministry of Defence's nuclear programmes have been raised regularly by the Defence Nuclear Safety Regulator (DNSR), with fears that working conditions and culture might not be sufficient to prevent a more serious incident. DNSR's annual report for 2012 stated that “a number of 'control of work' issues have arisen during the reporting period; this remains an area of regulatory focus”.