Hybrid submarines, an efficient alternative

DANNY LAM  –  Aug 15, 2017

15 Aug 2017

Outrageous cost estimates for nuclear-powered submarines tend to cloud Canadian thinking for recapitalizing its submarine fleet. The US Navy is presently building Virginia class nuclear-powered submarines for USD$2.6 billion per unit. At CAD $1.5 to $3B (assuming no cost overruns), DND’s proposal for extending the lives of its four Victoria class conventional submarines for another 6-18 years appears a comparative bargain. But there must be a better way.

Off-the-shelf submarine designs that are direct or equivalent replacements to the Victoria class, like the German Type 212s presently are in the 300 to 400 million euros range (U$350-470 million), Swedish Gotlands are in the U$200-300 million range, while the Japanese Soyru is around U$550 million. These costs are roughly comparable to the high end of extending the life of Canada’s existing fleet. However, they do not reflect foreign military sales “markup” and likely exclude the weapons suite – nor are these prices based on quantity.     

If any of these candidates can be built in quantity – and an exception made to arcane Canadian military procurement rules that require the design to be manufactured wholly in Canada or have restrictive industrial and technological benefit demands – it is undeniably possible to substantially lower costs.    

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. 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 like the CSC or Maritime Helicopter program. Another route to substantial cost savings is to share the development costs of major items like the propulsion and power plant with partners. 

Nuclear propulsion was a major innovation in submarine technology. It significantly extends endurance to the point where it is limited only by food and consumables, and crew stamina.

Technologies like air independent propulsion (AIP) or lithium batteries that 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 and extended under-ice missions that are unique to Canada. 

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.  

The dominant paradigm for a modern nuclear-powered submarine is for a steam generating reactor driving turbines that directly drive the propulsor or propeller. The French Barracuda offers a limited hybrid design that enables electric propulsion for low speed cruising and turbo-mechanical drives at higher speeds. The Tullibee (SSN-597) and Glenard P. Lipscomb (SSN-685) were two nuclear-electric vessels that experimented with the technology, but it was not competitive against nuclear-steam turbo-mechanical for blue water operations. At the other end of the spectrum, a “mini” 400 ton nuclear submarine NR-1 was used for many key deep-ocean, bottom-exploration tasks.   

Due to their endurance, nuclear submarines tend to be blue water, ocean-going vessels.     Los-Angeles and Virginia class fast attack submarines displace 6-8,000 tons. French Barracudas are about 5,000 tons, UK’s Astutes are 7,000 tons, while the Shortfin Barracuda (conventional version) is about 4,000 tons. Compared to the Upholder/Victoria class at about 2,500 tons, they are large vessels.    

A small 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 because nuclear submarines are historically optimized for stealth in blue water. Much of Canadian waters in the Arctic are relatively shallow, and along the Pacific and Atlantic coasts up to the continental shelf where Canadian submarines are most likely to operate. A fleet nuclear submarine (6-8,000 ton range) is neither necessary nor ideal for Canadian waters.  

The dominant design for nuclear propulsion places a premium on sustained high speed, even though most submarines cannot do so while maintaining acceptable radiated noise levels. Sustained high speed, except for “getaway” or transit, is a capability that is rarely needed. Because nuclear reactors react relatively slowly to throttling, it also means that nuclear energy generates a large infra-red signature that is a much bigger liability in littoral vs. blue waters. Hybrids offer a novel solution.

A nuclear-steam-electric hybrid is a potentially attractive alternative to the dominant nuclear turbo mechanical drive. One or more modular reactors can be used to generate steam to drive a turbine generator. The ability to completely shut down a reactor module, and tightly 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 lithium batteries. 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.

Building such a submarine within a small displacement (2,5-3,500 tons surfaced) 60 days endurance, transit speed of 20 knots, burst speeds above 30 knots, and state of the art signature management technologies and support for unmanned platforms would be cost prohibitive for all but the largest Navies.   

Canada, however, has potentially very good technologies that can contribute to a joint venture for a new hybrid nuclear submarine design. The Canadian SLOWPOKE reactor has been operating in Canada since 1971 and is licensed for unattended operation. A later variant was rated for 2-10MW per module, just about ideal for a small nuclear-powered submarine. It is conceivable that the design can be freshened, miniaturized, compacted and “fitted” into an existing conventional submarine design displacing 2,500 to 4,000 tons, though quieting radiated noise of a small displacement submarine is challenging and require considerable ingenuity and technical competence.

Packaged with a turbo-generator plant, a SLOWPOKE reactor can also have many civilian applications such as being a steam generating plant for low GHG heavy oil extraction SAGD facilities, or a stationary energy plant for Northern communities. The more units deployed, the lower the fixed costs. That will also spread the political constituencies in favour of the program from just the coastal provinces to Ontario, Quebec, Alberta, Nunavut, and NW Territories: A major consideration given the political fault lines in Canada for a multi billion dollar program.  

If Canada contributed a major portion of the development cost of a new modular nuclear power plant for a hybrid submarine, it can be used to negotiate a good price on the vessel. It will also be the only small naval reactor / power plant available that can potentially also be used on surface vessels like the Canadian Surface Combatant or civilian vessels – reducing GHG emissions from shipping potentially opens up lucrative markets for Canadian nuclear technology. Who might partner with Canada?

Germany, Sweden, France, Japan, Australia are all potential partners. Each nation’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 submarines, can contribute certain technologies, like lithium ion batteries (in which they excel). Any of these would deliver a state-of-the-art nuclear-powered submarine for a fraction of the cost of “going it alone” or the Australian “built in Australia” technology transfer model. The key will be that the new co-developed hybrid nuclear submarine must find additional markets beyond the needs of the partners. 

The question is, can such a new vessel be built in quantity (more than 20) for less than US$700 million a copy?  

Success in this program will forever banish the ghost of the DeHavilland Arrow.

It will be challenging, but Canadian ingenuity is up to it.

– Danny Lam