Nuclear sub

A Canadian Hybrid Submarine Design: A Case for the Slowpoke-2 Reactor

David Dunlop, 28 February 2020.

Nuclear propulsion of submarines is ideal for long distances and extended under-ice missions. But is there a better, more affordable and collaborative way? Off-the-shelf air-independent propulsion (AIP) submarines such as the French Barracuda Block 1A class being designed for Australia or the Japanese Soyru-class AIP design with lithium ion battery (LIB) technology are alternatives that extend the endurance of diesel submarines. But neither of these options are completely satisfactory for Canadian submarine needs. The dominant paradigm for a modern nuclear-powered submarine is a steam generating reactor driving turbines that directly drive the propeller. The French Shortfin Barracuda Block 1A being built for Australia offers a limited hybrid design that enables electric propulsion for low-speed cruising and turbo-mechanical drives at higher speeds, but is not competitive against nuclear-steam turbo-mechanical for blue water or Arctic operations.

Outrageous cost estimates for nuclear-powered submarines tend to cloud Canadian thinking about recapitalizing the submarine fleet. DND’s proposal for extending the lives of Canada’s four Victoria-class conventional submarines for another 6-18 years appears to be a bargain. But is there a better way? The first challenge to costs is volume. Development, or non-recurring engineering costs, make up a sizable percentage of the cost of a small fleet of subs. If an existing, proven, hull can be slightly modified, it is a major cost saver. That will require DND to end the habit of imposing onerous modifications that inevitably cause costs to explode. Another route to substantial cost savings is to share the development costs of major items like the propulsion and power plant with partners.

Technologies like AIP or LIBs extend the endurance of diesel submarines but introduce major compromises in performance. But neither of these options are satisfactory for Canadian naval requirements. With or without AIP, diesels are far too ‘short legged’ – they are dependent on logistically complex supplies such as liquid oxygen that deplete quickly; and the engines are mechanically complex. These are distinct disadvantages given the long distances missions that Canadian subs must undertake.

Whenever a diesel ‘snorts,’ it leaves a very visible plume of smoke and heat that is readily detectable. Radar can pick out periscopes or snorkels. Then there is the deafening noise of diesels, even when equipped with the latest quieting technologies. Thus, nuclear propulsion in some form is still the ideal for Canadian requirements. Due to their endurance, nuclear submarines tend to be blue water, ocean-going, and compared to the Victoria-class at about 2,500 tons, they are large vessels. A fleet nuclear submarine is neither necessary nor ideal for Canadian waters. A smaller nuclear-powered attack submarine that is large enough to support a good sized crew and carry unmanned systems would be ideal for Canada but, presently, none is available.

A hybrid submarine offers a novel solution. A fleet of hybrid nuclear submarines (6,000+ ton range) would be ideal for Canada. But building such a submarine with this kind of displacement with a 60 day endurance, transit speeds of 20 knots, burst speeds above 30 knots, state-of-the-art signature management technologies and support for unmanned platforms would be cost prohibitive for all but the largest navies. Canada does, however, have an excellent technology that can contribute to a joint venture with, say, the USA, France or Japan for a new hybrid nuclear/AIP submarine design – the Canadian Safe LOW POwer (K) Critical Experiment, or ‘Slowpoke-2’ reactor. This would be just about ideal for a smaller nuclear-powered/AIP submarine. A nuclear, battery-electric hybrid is a potentially attractive alternative to the dominant nuclear turbo-mechanical drive. One or more modular reactors can be used to generate power to drive generators or constantly top-up LIBs.

Slowpoke-2 Reactor

The ability to completely shut down a reactor module, and match energy demand with supply, reduces the amount of excess (waste) heat dumped – don’t forget, that heat dump is detectable. Machinery noise from the nuclear turbo-mechanical generator can be more readily controlled if the system is operated at (and optimized for) a relatively narrow power band with no requirements for rapid throttling as with a turbo-mechanical drive. Electricity generated can be stored in state-of-the-art LIBs. Reactor shielding can potentially make use of lead acid cells doing double duty. Electric power from batteries driving propulsors offer the prospect of extremely low radiated noise and yet maintain a high degree of ‘throttlability’ with only limited compromises in sustained high-speed cruising that would be a function of the nuclear plant’s power ramp and maximum output. Making the propulsor jets steerable and eliminating control fins is an additional benefit in minimizing the active signature.

One of the biggest advantages of Slowpoke-2 reactors in a modern hybrid AIP submarine design is that ‘snorting’ of the submarine would be a thing of the past as energy would be continually stored in LIBs for better under-ice endurance. This would also open up potential lucrative markets for this Canadian nuclear technology.

During the mid-1980s Canada briefly considered converting its Oberon-class submarines to nuclear power using a Slowpoke-1 nuclear reactor to continuously recharge the ship’s batteries during submerged operations. The Slowpoke-2 design is a larger, improved version of the Slowpoke-1 reactor. The upgraded design has a high ratio of neutron production to fission power, with a nominal power level of 20 kWA. A good deal of work has been done on potential marine applications of the reactor at Royal Military College in Kingston Ontario. The main advantages of the Slowpoke-2 reactor is the reliability and ease of use of this design. The Slowpoke-2 is small enough and inexpensive enough to make it accessible for smaller submarines. It is the only type of nuclear reactor licensed in Canada for unattended operation in automatic mode. In 2001 the Slowpoke-2 digital Integrated Reactor Control and Instrumentation System (SIRCIS) was implemented using professional development software. SIRCIS increased the functionality of the original analog system and improved the overall user interaction.

Who might partner with Canada? France, Japan and Australia are all potential partners. Each state’s existing or planned submarine designs are potentially good candidates. In fact, the French are already working on a new hybrid Barracuda variant for Australia. A collaboration with Japan, which has begun work on its next generation of electric Soryu-class AIP submarines, could contribute certain technologies like LIBs in which Japan excels.

If Canada contributed a major portion of the development costs of modular Slowpoke-2 power plants for hybrid submarines, it could be used to negotiate a better price on the subs, perhaps less than 1B CAD per sub (substantially lower than any standard nuclear sub being built today). It will also be the only small naval reactor power plant available that can potentially be used on surface vessels like the Canadian Surface Combatant or civilian vessels. As well it could reduce greenhouse gas emissions from shipping and potentially open up lucrative markets for Canadian nuclear technology.

The question is, can such a unique hybrid sub design be built in quantity (more than 20) for less than $1B CAD a copy? The technology of the Slowpoke-2 reactor is there, and has been constantly up-graded over several decades and is on the brink of success. An updated National Shipbuilding Strategy with this innovative hybrid submarine design would be a game-changer for Canada. Faith in this program by Canadians and the government will forever banish the ghosts of the DeHavilland Avro Arrow fiasco. It will be challenging, but Canadian ingenuity is up to it.


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