What Is A Nuclear Submarine And Why Would You Want One?

That’s where the US comes in. Its Virginia-class nuclear-powered submarine represents a modern engineering triumph. Its 34-foot-diameter pressure hull contains a S9G reactor likely rated at around 190 megawatts, comparable to the Russian OK-650 reactor in Project 971’s Akula class. The Virginia class, however, has a life-of-ship reactor core life of 33 years and doesn’t require refuelling. These capabilities were only achieved through decades-long development of a US “nuclear navy” in the form of more than 200 submarines. Overall, the US Navy has logged more than 6200 reactor years with 526 nuclear reactor cores over the course of 240 million kilometres, without a single radiological incident.

A US Virginia-class attack submarine under construction in 2012.  

The United Kingdom has also developed and deployed nuclear submarines for decades, and the Royal Navy’s Vanguard-class nuclear-powered ballistic-missile submarine and Astute-class boast a “life-of-ship” reactor core, far superior to the once-a-decade refuelling required of France’s Barracuda. To achieve this, the US and Royal Navies have always used very highly enriched fuel in naval reactors. But core lifetime has vastly increased by using burnable poisons that have a great affinity for thermal neutrons and therefore permit much more of the highly enriched fuel being loaded. Since the burnable poisons will be consumed at about the same rate as the highly enriched fuel, the result is an almost uniform critical control rod height throughout the core’s life. For the Columbia-class, the Ohio-class replacement scheduled to begin operations in 2031, the core life goals are increased by around 25 per cent to achieve a life-of-ship reactor core of 42 years.

The next best thing to a nuclear power plant is an advanced variant of conventional power – which militaries restricted from using nuclear power for political reasons, like Japan and Germany, are turning to. So are countries, like China, with relatively limited nuclear-powered submarine programs.

One approach many navies, including China’s Yuan-class submarines with their Stirling engines, have adopted is air-independent power that doesn’t require, unlike most conventional power sources, regular surfacing. This greatly extends the time a submarine can cruise at low speed without draining its battery and risking detection by raising an air intake and exhaust tube (for perhaps as long as two weeks). It also saves the main storage battery’s energy for relatively fast evasive manoeuvres (for perhaps as long as two hours). Air independent power’s biggest advantage is it provides tactical flexibility to the submarine commanding officer. They now have both greater luxuries to choose when they recharge their batteries and the ability to use higher speeds if the tactical situation warrants it.

The most advanced air-independent power system are fuel cells. They contain no moving parts, yielding a very low noise signature, and no depth constraints, with the only byproducts of combustion being pure water and heat. Only Germany has deployed this technology successfully thus far, selling it to South Korea, Greece, Portugal, Israel, and Italy with their German designed submarines. ThyssenKrupp Marine Systems proposed the Type 216 with a fuel cell air independent power system during the initial bid for Australia’s future submarine program.

Distinctly inferior

The next most popular air independent power (AIP) option is the Stirling engine employed in Swedish, some Japanese, and China’s current Yuan-class submarines. It has the advantage of being relatively easy to build and is less expensive. It also has the benefit of burning the same fuel as diesels. Downsides include suffering limited efficiency in using oxygen (around 35 per cent as compared to upward of 60 per cent for a fuel cell system) and requirements that products of combustion be pumped overboard, creating depth constraints and additional rotating machinery noises. These can be reduced with traditional passive noise isolation techniques but not eliminated.

But, despite having some fierce advocates, AIP is still distinctly inferior to nuclear power. AIP systems use liquid oxygen as the oxidiser, necessitating large, heavy tanks and cumbersome, dangerous procedures. AIP cannot be drawn down quickly: Stirling engines can run at up to 150 kilowatts per engine, and German Howaldtswerke-Deutsche Werft fuel cells can run as much as 120 kilowatts each.

AIP does not add to the time a boat can operate at its maximum speed. The rate at which it can convert stored energy to power is small. Fuel cells have the highest efficiency in oxygen consumption per kilowatt, but hydrogen fuel stored in outboard aluminium metal hydride cylinders must be ultra-pure. It takes 40 to 50 hours of “soaking” the solid metal cylinders with hydrogen to refuel them. Even with AIP, a commanding officer still only has an hour or two at maximum speed as the majority of the necessary power still comes from the main storage battery, with little additional coverage.

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For conventional submarine propulsion, lithium-ion batteries appear to be the way of the future. They have great power density and weigh much less than their lead acid predecessors, but early lithium-ion batteries have a problem with thermal runaway that occasionally caused them to combust. The US Navy’s Advanced SEAL Delivery System burned itself out due to a thermal runaway incident with a metallic lithium-ion battery. More recent technology includes composite-based plates using silicon or carbon nanoparticles. These are safer, not quite as powerful, and are batteries submariners could accept. Germany is beginning to install lithium-ion batteries in its Type 212 and Type 214 submarines, increasing stored energy by as much as 400 per cent compared to previous lead acid batteries.

China’s Jin-class nuclear submarine. AP

Japan is making the most of its constrained situation. Unlike Australia, it has a politically overwhelming memory of nuclear tragedy, preponderant military threats in immediate proximity, and massive heavy industries offering the best possible conventional propulsion technologies – all factors precluding nuclear propulsion for now but driving the most advanced possible alternatives. Japan’s next-generation Soryu-class submarines will have lithium-ion main storage batteries instead of AIP. The rationale is large storage tanks for liquid oxygen make AIP too volume intensive, and volume saved will be allocated to habitability.

Chinese specialists are scrutinising these developments carefully and seek to parlay China’s substantial, if still limited, lithium-ion battery industry into submarine applications. BYD, China’s largest rechargeable battery manufacturer, is the world’s largest producer of nickel-metal-hydride batteries. This is the basis for most automotive hybrids and some electrical cars today, although lithium-ion batteries are starting to emerge. BYD has aggressively pushed the development of lithium-iron-phosphate batteries, a metallic type that is completely recyclable. This type of battery’s automotive experience is very recent.

It’s still not clear whether BYD’s battery design is a game-changer or not, particularly from a naval perspective. Lithium-iron-phosphate batteries are not as powerful as other lithium-ion types, which may support BYD’s claims that its batteries are safer. BYD’s battery technology appears to be not nearly as powerful (perhaps roughly half as powerful) as the type scheduled for deployment on Japan’s modified Soryu-class and is not as competitive as an AIP system. More research also needs to be done regarding BYD’s safety record to see if it lives up to its advertising. Since a submarine battery is still much larger and the power requirements are considerably greater than the sort of battery BYD developed for its all-electric buses, BYD would likely have to improve power density significantly. Whether its chosen design can support this remains uncertain. And, in any case, China finally seems poised to make major nuclear-propulsion progress.

China’s Russian link

Mastering naval nuclear power is a key part of Beijing’s global ambitions at sea. China became the first Asian country and the fifth globally to successfully design, build, and commission a nuclear-powered submarine: the 1974 Type 091 Han-class. The first hull was laid down in 1967, but the Sino-Soviet split and Cultural Revolution delayed efforts. Beijing is now determined to achieve world-class results rapidly and continue to advance, and it should not be underestimated in the long run – especially as Russian assistance may accelerate its success substantially. In September 2010, China and Russia agreed to expand their co-operation in the development of floating nuclear power plants. Russia had finished the design for Akademik Lomonosov, which would have two 150 megawatt KLT-40S reactors – reactors that are closely related to OK-650 reactors on Russian third-generation submarines built in the mid-1980s through the 1990s.

Initially, China was reportedly considering importing reactor technology from Russia but later decided to use an indigenously produced 200-megawatt reactor, the ACPR50S, designed by China General Nuclear Power. This reactor started its development in 2012 and bears a striking resemblance to the Russian KLT-40S with its unique primary coolant arrangement that employs a pipe within a pipe, which is associated with Russian naval nuclear power reactors.

Today, China remains behind the US and Britain and continues to suffer major weaknesses in its nuclear-powered submarine performance and quieting. It has developed its own versions of foreign diesel and gas turbines – and if Russia has indeed shared a third-generation submarine reactor design, then the world should expect the next generation of Chinese nuclear submarines to finally close the wide technological gap.

China has deployed AIP on its most advanced conventional submarines and is working to progress to next-generation lithium-ion batteries. It still lacks experience with nuclear power for aircraft carriers. All three Chinese carriers under construction or operational thus far appear to use traditional oil-fired boilers and steam plants.

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The complex and demanding performance parameters of naval propulsion make this a difficult field to master. Piecing together foreign and indigenous technologies of civil and military origin has served China relatively well in some areas but will not ensure naval nuclear power success given the degree to which components must work together as a sophisticated system of systems.

Irresistible logic

However, if Russia agreed to lend China technical support in designing a high-power density reactor for naval applications, such as a floating power station or a submarine, this process could be much faster. And if the Australians believe this to be the case, that may be one factor behind its nuclear submarine decision.

Advanced types of propulsion, particularly nuclear, are guarded zealously by leading foreign powers. For these reasons, a robust partnership is needed to fully access them – exactly what Australia has just achieved with the US and Britain as well as what China may be gaining, to some extent, with Russia.

Australia’s way forward now certainly involves access to and incorporation of US nuclear propulsion technology. The United Kingdom may play a major role in the construction and by supplying former Royal Navy submariners to help train and crew the new Royal Australian Navy’s nuclear submarines. This new tri-national venture will take considerable time, money, and effort to achieve sea power in practice, but the logic is clear and irresistible. Canberra, facing strategically seismic threats from Beijing, received an offer previously extended only to London, and understandably went all-in on one of the most game-changing military technology deals for decades.

The benefits will begin long before Australian nuclear submarines actually hit the water – perhaps a decade hence. Trust and alliances are further cemented, sensitive information and key personnel are in the process of being exchanged, and mutual facilities access beckons. The upfront process is as useful as the eventual product. It’s true that Australia’s six Collins-class diesel-electric submarines must lumber on as a gap-plugger, and China may well pose its peak Taiwan Strait and regional military threat before Australia has a fully operating nuclear fleet. Australia’s risk, however, can be mitigated by the forward deployment of US and/or UK submarines to Australian bases.

But meeting the challenge starts with confronting it from the firmest possible alliance foundation. And an empowered and encouraged Australia has much to offer for immediate value – from trusted professionals to leading human and technical intelligence to uniquely situated basing and training facilities.

Australia’s fait accompli should be celebrated by those favouring robust allied sea power as a bulwark against Chinese aggression –and at least understood by all who believe in national interests and sovereign decisions.

This updated article draws partially on Andrew S. Erickson’s book Chinese Naval Shipbuilding: An Ambitious and Uncertain Course, specifically ”Underpowered: Chinese Conventional and Nuclear Naval Power and Propulsion” co-written with Jonathan Ray and Robert Forte.

Andrew S. Erickson is a professor of strategy in the US Naval War College’s China Maritime Studies Institute and a visiting scholar in full-time residence at Harvard University’s John King Fairbank Centre for Chinese Studies.

Foreign Policy

Source : https://www.afr.com/policy/foreign-affairs/why-we-badly-need-nuclear-submarines-20210922-p58tqm

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