BMT Defence Services completes Submarine Secondary Systems options study

BMT Defence Services Ltd announced today the completion of a study into Submarine Secondary Systems Options, as commissioned by the Ministry of Defence's (MoD's) Future Business Group last year.

A nuclear submarine's secondary systems provide the power for its propulsion and all the electricity needed to power onboard equipment and sustain life. Although there are no firm plans for new Royal Navy nuclear submarines beyond the Astute class currently under construction, the MoD - in line with the recently published Defence Industrial Strategy (DIS) - considered it prudent and timely to review the design and technology of submarine secondary systems.

"In line with the DIS and recognising the continued interest in the capabilities of nuclear submarines and the many technological advances across all the systems of a nuclear submarine, it has been a good time to carry out this study," says Professor Chris Hodge, BMT Defence Services’s Chief Electrical Engineer and a Fellow of the Royal Academy of Engineering.

BMT has undertaken a thorough assessment of existing and new technologies and compared potential capabilities, looking particularly at the scope for enhancement, simplifying systems and improving efficiency and affordability.

"While nuclear submarines' secondary systems are already very well designed and are reliable, resilient, compact and quiet, we’ve been completely open-minded in our wide-ranging search for improvements," says Hodge.

Unlike nuclear reactors in the commercial sector, which are physically large and operate at relatively steady powers, the naval equivalent operates over a wide range of rapidly changing power levels and need to fit within a small submarine hull. These constraints also apply to the secondary systems.

In the past, full-load efficiency was vital to achieve the necessary full submarine speed. This resulted in an efficient, well-balanced and well-specified full-power design from the reactor to the propeller, but part-load efficiency was not considered as important and existing secondary systems are therefore less efficient at part load.

"As a general engineering characteristic, it is difficult to design for good efficiency across the full power range of a propulsion system, especially where compactness is essential," says Hodge. "This difficult objective is now very much in mind though, because the lengths of time submarines operate from a single reactor core have increased.

"We must also remember that although high speed is important, it is rarely used: nuclear submarines spend most of their time at slow speeds with low propulsion loads. This means that improved part-load efficiency can greatly increase the submarine's operational life."

The study also considered the capability of various technologies to improve overall submarine through-life costs by reducing maintenance requirements and improving reliability. It is here that simpler systems can have the greatest impact by reducing procurement cost and maintenance.

Another consideration of the study was how best to distribute electrical power throughout the submarine. With highly reliable power supplies, systems have become simpler as alternative and back-up supplies are no longer needed. In all these areas – including power generation, propulsion and power distribution – there have been significant advances in technology.

Following the completion of the study, BMT will model a number of possible systems and undertake detailed cost-benefit analyses to determine the best solutions.