The Vulcan Naval Reactor Test Establishment in Scotland has assumed a third crucial role in the support of the Royal Navy’s nuclear submarine fleet.

The first Naval reactor core assemblies, which powered the early generations of ballistic missile and hunter-killer submarines – including today’s Swiftsure and Trafalgar-class boats – were all put through trials in the DSMP, or Dounreay Submarine Prototype at Vulcan, near Thurso in Caithness.

The military site, on the north coast of Caithness has five Naval staff heading a workforce of around 300 Rolls-Royce workers.

Royal Navy reactors have been put through their paces at Vulcan in a rigorous regime of tests since the first, Core A, went critical in 1965, eight years after work began on building the complex.

That assembly of radioactive fuel modules and control rods heated water in a primary circuit, which passed its heat to water in a secondary circuit, creating the steam which drove the turbines. The materials and specifications have changed over the years, but the concept is the same.

That first core, along with subsequent versions (B, Z, G and H) were all built by Rolls-Royce, based in Derby, which has been operating the reactors and associated equipment at Vulcan from the first day.

Each reactor went to Vulcan to be tested ahead of use in submarines, so that any problems which may have arisen in a particular design would have arisen at Vulcan long before it became a problem in an operational boat.

The land-based reactor is always at least two years ahead of its sea-going counterparts – in the case of Core A, depletion occurred by 1967, by which time a great deal of experience and useful data had been gathered for operational purposes and for feeding back into the development of new reactors.

The Vulcan reactor – designated Dounreay Submarine Prototype 1 or DSMP – also served as a full-scale training rig, allowing RN nuclear plant operators to gain hands-on experience.

But by the time Core A was burned out, a simulator had been opened, and training transferred on to it that same year.

Core A was removed in March 1968, and after the plant was overhauled, Core B was installed – which gave Vulcan the honour of achieving the first refuelling of a submarine reactor in the country. Maintenance and refuelling procedures still number among the prime tasks of the Vulcan site.

Core B went critical in June 1968, and far outperformed its predecessor before it closed down, its job done, in 1972.

By this time the Admiralty Research Test Establishment, as it was originally known, had been commissioned as HMS Vulcan (the HMS prefix was lost again in 1981), and Core Z was the centre of attention.

That reactor had been installed in 1974 after another major refit to the DSMP, and it lasted more than a decade. Core Z is fitted to the Navy’s current fleet of hunter-killer Swiftsure and Trafalgar-class boats.

With the completion of the testing of Core Z, and the commissioning of the Shore Test Facility (STF) for PWR2, DSMP was defuelled, decontaminated and brought back into service as the LAIRD, or Loss of coolant Accident Investigation Rig Dounreay, proving the soundness of the Rolls-Royce reactor and support systems under the most challenging of situations.

LAIRD was commissioned in June 1987, and shut down for modifications just over a year later on successful completion of the first phase of trials.
Restarted in July 1989, the LAIRD was the only full-scale plant in the world capable of doing this specialised task.

LAIRD ran more than 250 trials in five years, using a giant electrical heater to reproduce the conditions in a nuclear reactor at the point of shut-down.

And it is this ability, to create simulated nuclear power plant conditions, that has opened the door to a third lease of life – one which not only provides work for the specialised equipment and the technicians who operate it, but which also saves the Ministry of Defence a tidy sum.

A major contract was awarded to Vulcan and Rolls-Royce in 1993 to refurbish the main coolant pumps from British nuclear submarines, a task which required the kind of precision and high levels of skill which Vulcan had in abundance.

Previously, these large pumps had been automatically replaced at approximately every ten years, at considerable cost, as they needed to be as close as is humanly possible to perfect reliability.

But the Vulcan organisation – currently headed by the Naval Superintendent Vulcan, Cdr Charles Hume – saw an opportunity to land its first major commercial contract outside the operation and maintenance of nuclear reactors.

Pumps arriving at the MCP (Main Coolant Pump) facility at Vulcan from a submarine in refit – in recent months the site has handled equipment from HMS Spartan and HMS Trenchant – are decontaminated, then stripped and inspected in the designated decontamination area.
Vulcan then issues a report with its findings and recommendations to the Ministry of Defence.

The MOD will then, if all is well, reply with approval for the recommended course of action, and refurbishment begins.

The pumps are brought back to original specification and then reassembled ready for testing on the LAIRD.

The tolerances to which the team work are staggering – down to 0.002mm in certain elements.

The pumps are also checked for stress and cracks by metallurgists.

They are balanced and endurance-tested – for as long as four to six weeks, 24 hours a day – before being returned to the workshop where they are again stripped down to the basic components and thoroughly inspected.

Any source of noise in nuclear submarines makes them easier to detect and less able to detect external threats, so Vulcan staff dynamically balance the coolant pumps under service conditions to minimise such noise.

Each pump will undergo at least four calibration runs before computers work out the optimal number and positioning of counterbalances to keep the pump running smoothly and silently.

The components are then transferred to a clean room, where they are cleaned to a high standard, reassembled (a process which can take five days) and finally sent to the submarine for which they have been earmarked.

They do not have to return to the same boat – the reactor systems in every boat are identical, and by swapping sets around refits are not subject to delay by the lengthy refurbishment process.

The painstaking nature of the work means Vulcan takes over a year to refurbish a set of pumps to the most exacting standards, and in the last year the team have just proved themselves capable of refurbishing pumps from the reactors on Vanguard-class boats as well.

The process is laborious, but necessarily so, eliminating any chance of error along the way.

Everything is done by the rulebook, and a Rolls-Royce expert will watch at least one reassembly for each set of pumps, as well as checking for the resolution of any abnormalities identified at an earlier stage.

LAIRD’s unique ability to simulate the conditions in a nuclear reactor allow the pumps to be tested safely in situ before they are refitted in the real thing.

Cdr Hume said: “This is a classic example of innovation in the use of Ministry of Defence facilities and the considerable skills base at our disposal, which has enabled significant cost savings to be realised.

“Not content to rest on their laurels, the local team continue to improve their processes year on year, and have won a number of industry awards in so doing.”