By David Dunlop, 13 February 2023
It appears that Australia's AUKUS submarine decision will be coming in March 2023 and it may not be anything that most expect. It was anticipated that either the Virginia-class or Astute-class SSNs would be selected. It appears however that neither one of these boats may be finally selected, but a future replacement of the UK Astute-class called the SSN (R). There are several scenarios that may occur ranging from leasing Astute-class SSNs by Australia or possibly refurbished Los Angeles-class SSNs to provide an Australian SSN attack capability sooner before the SSN (R) program comes on stream. Here are some Breaking Defence articles by Colin Clark and Tim Martin on 10 February 2023. There's another interesting article by Nick Childs (Senior Fellow for Naval Forces and Maritime Security), 23 January 2023 called "AUKUS and the Nuclear Reaction to this." See the following.
https://breakingdefense.com/2023/02/growing-signs-australias-new-nuclear-sub-will-be-british-design/
https://www.iiss.org/blogs/military-balance/2023/01/aukus-and-the-nuclear-reaction
17 thoughts on “Australian AUKUS Sub Decision Coming March 2023”
Hello David,
Just a few thoughts.
The first article quotes “…select…a mature design…where there already is a production run…” that sounds familiar :) we didn’t have much luck with that one for the CSC.
Australia has the ambition for a nuclear boat yet has no existing nuclear capability. That’s putting the cart quite a ways in front of the horse. Australia’s current energy mix is coal heavy to say the least https://www.energy.gov.au/sites/default/files/2022-09/2020-21_Energy_Flows_20220820-v19a-p
Building that technological capacity will take a very long time.
Lastly, I am surprised no French speakers have pointed to the ridiculous sound of AUKUS or [au cul]. Freudian slip? Someone will come out of this with a sore stern, and I’m not convinced it will be China.
Regards!
Hello Curious Civilian. Yes, you are quite right. Australia does not have a “real” nuclear capability. The prospect of nuclear power in Australia has been a topic of public debate since the 1950s. Australia does have one nuclear plant but it is not used to produce nuclear power, but instead is used to produce medical radioisotopes, research and analysis. Australia has 33% of the world’s uranium deposits and is the world’s third largest producer of uranium after Canada. In that respect, Canada is much further ahead as we do have several nuclear power plants dedicated to produce electricity. We also produce medical nuclear isotopes and we are strongly considering Small Modular Nuclear Reactors (SMNRs) in the “near” future in Saskatchewan, Ontario and New Brunswick. So in those respects Canada does and will have more nuclear expertise compared to Australia. But Australian SSNs are a different ‘kettle-of-fish’ for both countries and it will take many years for Australia to acquire that kind of expertise with any SSN technology that it decides to go with. That is why in my opinion Australia will decide to go with the future UK SSN (R) design. This SSN is still on the drawing board to replace the Astute class and will be longer and heavier (approximately 9,200 tons anticipated) with Vertical Launch Tubes and will be more like their Dreadnaught SSBN cousins now being built by Britain to replace their Vanguard class. It will take at least until 2040 before the first SSN (R) boat comes off-the-line for the Brits, so there is some time for Australians to gain that expertise before they do buy their first SSN (R). In the meantime, Australia will most likely lease either refurbished Los Angeles or Virginia class SSNs in order to gain that knowledge. So that’s about 17-18 years from now. Any which way you look at it though, it will be somewhat more expensive for Australia to do this but, they should be the wiser in the end.
@Curious Civilian Part of the CSC problem is that Canada bought a frigate that is intended primarily for ASW, then decided to fit Aegis (very expensive system) into it to make it more General Purpose (All rounder).
Aegis is a very power hungry integrated system which requires a large hotel load to run the sensors, this means the CSC power plant needs refining not to mention the COG COB calculations as aegis is heavy.
I believe Blair you are comparing apples to oranges as far as the AEGIS ‘system’ is concerned. You are correct in that the system is heavy. However the CSC Frigate is not using the AB AEGIS ‘System’ at all. Only the AEGIS software associated with that system as it relates to the CSC Frigate CCS 330 Combat Management System (CMS) in conjunction with the SPY 7 (V3) and the X Band Illumination Radars. These radars are not nearly as heavy as the AB Flt III ‘System’ and I’m sure that Lockheed Martin and the RCN have taken weight into account when designing the CSC Frigate. Cheers!
Hello again,
On the same breakingnews article, note from Defense Minister Richard Marles:
“Adding some detail to the discussion in a prepared Thursday speech before the Australian House of Representatives, he defended the likely high quantity of foreign content in the new subs, noting that almost all major Australian weapon systems depend on foreign content.
“Some argue that Australia’s reliance on our partners for the acquisition of naval nuclear-propulsion technology gives rise to a dependence that undermines Australia’s sovereignty,” Marles said. “Yet the reality is that almost all of Australia’s high-end capability is developed in cooperation with our partners. Submarines are no exception. And that dramatically enhanced capability dramatically enhances our sovereignty.
So Australia’s defense is highly dependent on parts and equipment from foreign sources (primarily US and UK), with relatively limited native production capability. As the Ukraine fiasco shows, logistics and ammunition/parts production is key. Should a conflict involve Australia against China, the former’s supply chains will be severely constrained, and that “foreign content” will be absent. How does that then enhance sovereignty?
A key lesson should be that sovereign countries develop their own capabilities. Once they can comfortably extract, process, produce and manufacture what they need through their own labour, and demonstrate a high degree of self-reliance, then they can talk about sovereignty. Most NATO members have actually shown themselves to not be sovereign.
Regards!
Hello again Curious Civilian. Defence Minister Richard Marles’ comments seem to be bang on WRT Australia’s SSN procurement down the road and makes a lot of sense. The same could also be said for Canada’s submarine decisions as well. I believe that Canada should procure a seat at the table soon as it relates to the AUKUS nuclear technologies program as well and decide to go the same way as Australia has done. Call it “AUCANUKUS”. No matter what happens for Australia next month, both Canada and Australia will be locked into US technology with a lot of US equipment with any submarine they both decide to buy in the future. If Canada does not take advantage of this opportunity with our allies, then the only other option I can see with a replacement sub for our Victoria class would be the Japanese 29 SS Soryu class submarines with LIB technology for our future sub capability.
Personally I can’t seen Canada going down the AUKUS route and obtaining SSNs or becoming part of it, but I do agree that SSN(R) would be the likely candidate for Australia. On a side note I also would like Canada to be part of the agreement so they can have a seat at that table, plus with shared technology and platform sharing that could make a big difference in cost per platform as well as reduced R&D costs .
I would also be hesitant regarding the replacement of the Victoria class with the Soryu class or even the Taigei. To note, as it currently stands the Soryu production has already ended being replaced with the Taigei class.
While this submarine is very capable especially in endurance with it not being fully AIP that means unfortunately under ice capability is not within its scope and the Arctic region is one of Canada’s focus areas and main strategic weaknesses.
Sorry Blair. My bad. You are correct in that the 29SS is called the Taigei Class and is a successsor to the Soryu Class. It does not have an AIP capability, strickly LIB batteries which will decrease their max speed somewhat, however their LIB technology with this class has dramatically improved over the last few years to the point of Japan not having to worry about AIP technology with this class as they are even quieter than the Soryu Class (SS512). They have said the first of class will be a “test vehicle” only and they will build the rest of the Taigei class based on lessons learned with the Taigei submarine. They have improved and modularized the new sonar of the Taigei to make it even quieter than the Soryu class and have reduced fluid noise and snorkel power generation compared to the German type 212CD/216. The silent drive system and the new high-efficient LIB power storage system with more LIB batteries compared to the Soryu class, dramatically increases submerged time however as said this comes with a slight decrease in max speed The class will also be approximately 100 tons heavier compared with the the Soryu class but will also be slightly smaller in over-all length. Their second in the class is scheduled to be commissioned next month in March 2023. On another not being part of the “AUCANUKUS” technology program would be a good move for Canada perhaps not getting SSNs in return but, who knows in the future. The 29SS design from Japan however seems to be a good design for Canada and by 2040 when the Victoria class is ready to finally be replaced, could be a very good option for us to invest in and buy. By that time, Japan will most likely have a replacement design for the Taigei class that would fit Canadas needs as an ocean going large, comparable to nuclear submarines, for both world-wide and high-Arctic missions in my opinion (IMO). Cheers!
The main issue I do find with Japanese submarines is that they have short service lives on average (usually 20-25 years) Canada is not going to want to spend billions replacing the Victoria’s only to do it again 20/25 years time, I think they will be looking for a 30+ year platform (probably closer to 40 years).
The Soryu is an awesome piece of kit and is a great submarine with a lot of technology inside it, I managed to get a tour of the Zuiryu in Yokasuka a few years ago and yes its a damn good boat. Problem with Japan is a lot of the technology is American so it would require American approval for transfer (as did the Australian bid), and while Canada and the USA are close allies and partners I am somewhat hesitant that this will happen.
The 212CD design can out-perform in terms of submerged endurance than even the Taigei the 212A recently did an entire 3 week transit without coming up to snort or anything something even the Taigei cannot do and with the CD being much larger that speed / range curve increases as they plan more fuel storage in the new boat.
Also to note the first boats could be in Canadian hands by 2030’s easily especially with the new building yard. Germany isn’t opposed to doing a tech transfer so they can be built in Canada either something the Japanese are not fond of doing.
The Taigei with even half the submerged endurance capability makes it vulnerable in the arctic, it can take days to find a polynya to surface through and if you don’t have that on tap then ultimately you’re risking the boat and crew. (not to mention the lack of speed could potentially cause another handicap)
Japan currently is working on a replacement for Taigei. It’s something they do as par for the course.
Indeed this does appear to be the lighter system in terms of hardware weight but how much is the hotel load going to be ?
The type 45 for example has had a lot of issues due to the high hotel load hence why we did the PIP upgrades, but this upgrade also adds weight to the hull which has an effect on speed overall.
Indeed I’m sure they have taken all relevant measures into account, it’s just personal experience with the type 45 program has lead me to be somewhat cautious because there we got it so wrong.
Hello Blair. It would be very interesting to find out exactly what the Japanese are working on now for a replacement for the Taigei class. Perhaps a strengthened sail and outer hull for arctic ice “breakthroughs” to start and improved LIB Technology for longer under-ice endurance. Perhaps missile silos as well? As you can tell I am very bullish on new/future Japanese subs as opposed to the German Type 212CD/216 as I believe Japanese submarines have better possibilities for the Canadian high arctic sub capabilities. Only my opinion own though.
Hello Blair. It appears from your last comments on SMRs that perhaps we are not as far along with SMRs/SMMRs as we need to be and much more research and technical aspects of of these SMRs needs to happen before Canada could use these reactors in any “Hybrid” sub build. Neutron leakage seems to be the biggest problem to solve first along with other problems. I really appreciate your technical expertise on SSNs and how they operate. So turning off a reactor at sea is not as easy as one would think. Perhaps just leave the reactor in a “hot standby” mode at all times. LIBs also seem to be another problem for now until the technology catches up. The Taigei class 29 SS seems to be a great way to go however how “safe” are they at present. Obviously the Japanese seem to be operating them with fewer problems now and perhaps by the time Canada is ready to replace the Victoria class, the LIB technology will be much impoved and safer. Again thanks Blair for your input and expertise. Cheers!
Let me bring in some thinking outside the box: what about a Nuclear Submarine based on a small micro reactor?
Out there small modular reactors technologies are soon to be released into the markets. One of those reactors, Westinghouse’s eVinci micro reactor (1) might offer the basics for a Canadian nuclear submarine. First, it is close to be commercially available (2), not military grade technology. Since the nuclear fuel is low enriched uranium (LEU) the U.S. should see no inconveniences to authorize its use for the Canadian Navy. There is already an ongoing project for a test plant in Saskatchewan (3) which might provide important lessons and experience.
Second, the electric power provided (5 MWe) would suffice to propel the boat at up to nearly 20 knots, assuming displacement within the range of 4000 to 5000 tonnes. While other nuclear submarines are faster, they also require a much larger reactor and military grade Uranium (HEU). At the end of the day, for patrols under the Arctic, speed of 8 to 12 knots (submerged) may probably fit the purpose.
One advantage of this technology, beyond its limited volume, is the little need for auxiliary systems and a reduced number of moving parts such as pumps, which also leads to lower supervision requirements. That’s why vendor promotes it as a “nuclear battery” more than a “nuclear plant”.
Finally, even tough the eVinci microreactor should be replenished every 8 years, depending on the operating conditions, this could be done during the regular long-term overhauls, as French do refuelling of their nuclear submarines. Moreover, the modular and encapsulated nature of this reactor makes it easier to replace it (compared to replenishment) and then work on the exhausted module for disposal at more appropiate premises.
Might the eVinci micro reactor be suitable for a submarine? For sure there would be a tremendous amount of further work to develop and “navalize” this reactor, still I believe it should be an option to explore for the expert group defining the future Canadian Patrol Submarine. Could even be previously tested in one of the polar icebreakers by using a containerized trial unit connected to the electrical system of the vessel.
That being said, AUKUS is more than just about submarines. It involves intelligence, AI and other forms of collaboration to which Canada should join (IMO).
References:
1) https://www.westinghousenuclear.com/energy-systems/evinci-microreactor
2) https://www.world-nuclear-news.org/Articles/Canadian-review-of-eVinci-design-begins
3) https://www.src.sk.ca/news/westinghouse-and-src-advance-micro-reactors-canada
Hello J. Cañadas M. Yes, I believe that emerging Canadian technology in Small Modular Reactors/Small Micro Modular Reactors (SMRs/SMMRs) would be ideal for a Canadian Hybrid/LIB Submarine capability I wrote an article on this several months ago and offer it here for your consideration. See below:
A Canadian Hybrid Submarine Design
A Case For The “Small Modular/Micro Reactor (SM/MR)”
Nuclear propulsion is ideal for long distances and extended under-ice missions that are unique to Canada. Off-the-shelf AIP submarine designs that are direct replacements to the Victoria class, such as the French Barracuda Block 1A class, or the Japanese Taigei 29SS class design with Lithium-Ion Battery (LIB) technologies or the German Type 216 submarine are interesting alternatives that extend the endurance of diesel submarines. But none of these options completely satisfactory Canadian submarine needs. The dominant paradigm for a modern nuclear-powered submarine is a steam generating reactor driving turbines that directly drive the propulsor or propeller. The French Shortfin Barracuda Block 1A 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 for recapitalizing its submarine fleet. DND’s proposal for extending the lives of its four Victoria class conventional submarines for another 6-18 years appears a comparative bargain. But is there a better, more affordable and collaborative way?
The first challenge to costs is volume. Development, or non-recurring engineering costs make up a sizable percentage of the cost of any submarine fleet. If an existing, proven, hull can be slightly modified, it would be 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 air independent propulsion (AIP) or LIBs 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, diesel submarines 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. Then there is the deafening noise of diesels, even when equipped with the latest quieting technologies. Thus, nuclear propulsion in some form is still ideal for Canadian requirements. Due to their endurance, nuclear submarines tend to be blue water, ocean-going vessels. Los-Angeles and Virginia class fast attack submarines displace around 8,000 tons. French Barracuda SSNs are about 5,300 tons, UK’s Astutes are over 7,000 tons, while the Shortfin Barracuda (conventional version) is about 4-5,000 tons. Compared to the Victoria class SSKs at about 2,500 tons, they are large vessels. A fleet nuclear submarine (6,000+ ton range) is 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. Canadian submarines are most likely to operate in Canadian waters especially in the Arctic, Pacific and Atlantic coasts up to the relatively shallow continental shelf. A Hybrid/LIB submarine would offer 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 unlimited endurance, transit speeds 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, does however, have an excellent emerging technology that can contribute to a joint venture from say the USA, France Germany or Japan for a new hybrid nuclear/LIB submarine design such as the Canadian Small Modular Reactor (SMR) or Small Micro-Modular Reactors (SMMRs) now being developed right here in Canada by Canadian companies. These SMR/SMMR reactors would be just about ideal for a smaller nuclear-powered/AIP submarine. A nuclear, battery-electric (LIB) hybrid is a potentially attractive alternative to the dominant nuclear turbo mechanical drive. One or more of these SMRs of say 20-30 MWe of power each could be used to generate power to drive generators to constantly top-up LIBs. The ability to completely shut down a reactor module, and tightly match energy demand with supply, reduces the amount of excess waste (heat dumped). 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. Electric power from batteries driving propulsors offer the prospect of extremely low radiated noise and yet maintain a high degree of “throttle-ability” 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 SMRs/SMMRs in a modern Hybrid/LIB submarine design is that “snorting” of the submarine would be a thing of the past as energy would be continually stored in much improved LIBs for much better under ice endurance. This would also open up potential lucrative markets for this Canadian SMR nuclear technology. The Canadian developed SMR/SMMR reactor systems could be made small enough and inexpensive enough to make it accessible and cost-effective for smaller nuclear submarines.
Canada is uniquely positioned to quickly develop the SMR/SMMR technology through National/International companies such as: The Atomic Energy of Canada Limited (AECL); Global First Power -an Ultra Safe Nuclear Corporation (USNC)/Ontario Power Generation collaboration; Chalk River Nuclear Laboratories (CRL) and UK based Moltex Energy. So, who might partner with Canada? The US, UK, France, Germany and Japan are all great 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. A collaboration with Japan, which has begun work on its next generation of electric Taigei class submarines, can contribute certain technologies, like LIBs in which they excel. SMRs/SMMRs would also be an excellent and clean source of power for future surface vessels as well.
Conclusion:
If the Canadian government contributed a major portion of the development costs of Small Modular Reactors or Small Micro Modular Reactor power plants for hybrid/LIB submarines, it can 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 world-wide). 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 (CSC) or even civilian vessels, reducing Green House Gas (GHG) emissions from shipping and potentially opening up lucrative markets for Canadian nuclear technology. The question is, can such a unique hybrid/LIB sub design be built in quantity (more than 20) for less than 1B CAD a copy? The technology of the SMR/SMMR reactors is here now, and has been constantly up-graded and miniaturized over the past several decades and is on the brink of success. An up-dated NSS Plan with this innovative hybrid/LIB 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 Arrow fiasco. It will be challenging, but Canadian ingenuity is up to it.
Hello David!
Good to know we row in the same direction. First I thought I had missed your article, later I have realized that you probably were referring to this one:
A Canadian Hybrid Submarine Design – Canadian Naval Review [https://www.navalreview.ca/2020/02/a-canadian-hybrid-submarine-design-a-case-for-the-slowpoke-2-reactor/], dated three years ago now. Time passes by so fast! I had then also commented your article (as JMCanadas) , as you may see below it.
While I mostly agree with your expressed ideas, on one side I am going a step further and bet for one of those microreactors, the eVinci, as it seems to me to be the one which needs less space and less moving parts, probably the most reliable and easy to maintain. Still these are only impressions, it is the RCN who counts with professional staff and would have access to the relevant information to analyze and study the different alternatives.
On the other side, just a little comment, I can not agree with this sentence: “The French Shortfin Barracuda Block 1A 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”.
While usually there is a lot of secrecy on the data of the SSNs, if we could rely on Wikipedia, either the English or the French version, the Barracuda/Suffren class features two Turbo-generator groups, 10 MW (electrical) each, which might drive the boat to a speed over 25 knots (1). I would definitely not say it is a “limited hybrid design (…) for low speed cruising”, neither say “is not competitive”. While Barracuda’s 25+ knots might not “compete” with Astute’s 30 knots, these French SSNs offer instead reduced crew (60-65 only) and dimensions. As for Arctic operations, even though the use of pump-jets may obviate the problem of ice blocking the propeller, it is usually preferred the electric drive over the mechanical one, as the first will disconnect (as a fuse) in case of blockage.
Nevermind, overall, as I said, I am delighted to share the main perspective with you.
Regards.
(1) 20 MW (electrical), according to my own estimates, is most probably quite enough power to provide the mentioned 25 knots for the Suffren-class boats, according to their displacement. In any case, just one such turbo-generator (leave the other one as reserve) would allow to reach more than 20 knots, for which the power required must be in the range of 6 to 8 MW. Please correct me if I’m wrong.
Hello J. Cañadas. Yes, my article was in the CNR for Forum members to comment on a few years ago. I am by no means an “expert” on nuclear technologies related to SSNs and percentage of U-235 required to produce nuclear fission for SSN submarines, but from what I understand Canada has taken the lead on SMR/SMMR technology. Both the US & UK use Highly Enriched Uranium (HEU)-about 93% in all of their SSN boats. That’s why their nuclear powered fuel lasts well over 30 years for their SSNs, as is probably the case for Russia, China & India as well. From what I understand, U-235 must be enriched to at least 50% in order for SSNs to operate. I would presume that the French Barracuda/Suffrin class would not enrich their u-235 for uranium as much but at least to 50 or 75 % but not as high as the US/UK boats. That’s probably why their fuel will not last as long (around 20-25 years). I believe that a Canadian SSN with SMR technology could use between 50-75% U-235 enrichment in order to produce a minimum of 10 MWe power output for each generator in order to produce “sprint” speeds of around 30 kts and cruise at 15-18 kts. One generator could be used to continually charge the LIB batteries so that when the reactor is in “hot standby” or “shut down”, would give LIB battery speeds of up to 12-15 kts for up to 20+ days of cruising. As I said, I am by no means an expert on nuclear SSN technologies and my assumptions may be well off. As this Canadian technology becomes more apparent in the future, we should begin to know more. If any more experienced CNR forum members have more insight on this topic, I would really appreciate your input. Cheers!
Currently the UK uses highly enriched (95+%) U235 that gives our boats the ability to operate without refuel for 25+ years. The French Rubis, Suffren and Charles De Gaulle platforms don’t use such highly enriched uranium hence they must be refueled after only 7-10 years which is a very expensive process.
SMR reactors being a smaller high yielding power low fuel reserve reactor (fast breeder in many cases) will require highly enriched uranium 95%+, they also produce around 5 times the waste of a normal reactor.
Links for reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9191363/ https://www.wired.com/story/smaller-reactors-may-still-have-a-big-nuclear-waste-problem/
With regards to running a hybrid Nuclear Electric system this has been tried before indeed the Soviets first put the concept to the test using a Project 651 modified to 651E (NATO Juliet class) submarine.
Given the state of their technology it actually by all accounts didn’t turn out so bad, it is indeed possible to run a hybrid system.
The problem arises when you constantly switch on and off a reactor, even our current generation is not designed to operate in such a manner, also even molten salt reactors produce Xenon gas which at low power rates doesn’t burn off and could ultimately poison the reactor vessel meaning that puts you in a very bad situation as you have to burn off the Xenon to get started again or leave the reactor shut down for an extended period for the Xenon to dissipate.
Simply turning on and off the reactor even a small one would not be wise you would have to keep the pile hot to produce the required output.
Current SSNs from a shut down state take many hours sometimes days to restart reactors back to stable levels, by that time your Lib batteries at 15 knots transiting speed would be all but dead.
Further more a reactor even a small one takes months to fully cool down its why when we decommission power plants or submarines we cant simply defuel right away in many cases it takes several years just to let the pile cool.
Reactors must be kept stable they do not like instability and to do that it has to be either on or off, no dancing about with it by having it on for a few days then off for a few days you could end up causing mechanical failure and pile degradation.
SMRs and nuclear reactors in general are designed for base loading, they are not designed even SMRs to provide on demand power hence why when you look at power plants across the world the nuclear ones are always on but coal oil and gas have shut down times usually during off peak load times, the same is true for a nuclear boat, therefore the Lithium batteries would only be an accessory power source when hotel load was in higher demand.
Moving on to the next part Lithium Ion batteries yes they are fantastic power stores and have extended lives over traditional lead acid ones but they do come with their own set of issues as the JMSDF found out in the early stages of the Soryu class boats.
Following Quote taken from Applied Sciences Fire safety risk analysis paper Link:https://www.mdpi.com/2076-3417/11/6/2631
4.2. Fire Risk—Lithium-Ion Batteries
The various failure modes of lithium-ion batteries are shown in Table 3, many of which lead to overheating. Safe operation of lithium-ion batteries can be assisted by a Battery Management System, however this is also has its own failure modes and vulnerabilities.
Most pertinent to fire risk is thermal runaway, a process where the uncontrolled temperature increase of a cell can lead to self-sustaining exothermic chemical reaction causing fire and potentially explosion [42].
For a large submarine which will require thousands of cells to be tightly packed, this brings the added risk of cascading thermal runaway where the heat from cells undergoing thermal runaway is transferred to neighbouring cells, in turn triggering further thermal runaway [39]. The typical stages of thermal runway are described in Figure 5 [40]. Thermal runaway can occur at temperatures of 150 °C, although the temperature at which thermal runaway is triggered can depend on failure mode, cell geometry and cell chemistry.
Overall the risks with the Lithium Ion batteries are manageable but putting it with a SMR and then introducing a incident maybe a little too much to bare.
That said however I do think by the time we get around to eventually sorting out the submarine issue in Canada the technology would have matured enough to make this hybrid possible.