Hi Shawn re your June 1, 2025 comment:
South Korea's (SK's) KSS-III Batch III might turn out to be nuclear powered - a true SSBN or
SSN-SSBN hybrid. Various countries, like France with its K-15 reactor could help SK. SK has also experimented and built reactors for decades and
considered responses to Japan's Mutsu nuclear powered ship https://gentleseas.blogspot.com/2016/06/japanese-nuclear-propulsion-1-mutsu.html
Judging by public sources and Fleet Base West's Indian Ocean positioning
Australia's SSKs rarely visit NZ or South West Pacific islands. Further north of the Sydney base may be more likely.
Due to differing SSK vs SSN electrical fitouts, differing balance/buoyancies and in fact
far differing internal arrangements retrofitting even a small reactor into an
operational SSK has never occurred, to my knowledge. I think a French Navy non-operational, Daphne-class SSK was used as a reactor testbed (?) in the 1960s-1970s prior to the launch of the first Rubis class SSN in 1979. https://www.lynceans.org/wp-content/uploads/2015/09/Part-4_UK-France-Others-60-yrs-of-marine-nuc-power.pdf
page 56 onwards, may provide clues.
Retrofitting an intentionally small, hence low power, small modular reactor
(SMR) makes little sense particularly relying on an SMR with molten salt
coolant.
The US experimented with an earlier USS Seawolf (SSN-575) (built in the 1950s)
being the only US submarine built with a sodium-cooled reactor. That Seawolf's
S2G reactor was a liquid metal (sodium) cooled, beryllium-moderated nuclear
reactor. The Seawolf's sodium-cooled reactor faced challenges, including leaks
in the steam generators and performance issues. Its was later replaced with a
standard PWR. See https://en.wikipedia.org/wiki/USS_Seawolf_(SSN-575)#Comparison_to_Nautilus
The USSR also attempted molten salt in its Alfa-class SSNs https://en.wikipedia.org/wiki/Alfa-class_submarine#Propulsion
with negative results. In emergency shut
downs molten salt reactors freeze - preventing restarts - requiring reactor
replacements. Pier side heating was essential.
I regrettably reckon there is little SSK to SSN retrofit or alternative reactor
coolant flexibility. Otherwise someone would have tried retrofitting SSK to
SSN.
Too little is known about the possible Wuhan mini-SSN to draw conclusions.
https://www.orfonline.org/expert-speak/subsurface-setbacks-china-s-submarine-accident-in-wuhan
Cheers Pete
8 comments:
Pete I share your skepticism on this one too (SMRs to convert SAsKs to SSNs). I will leave the reactor design questions to others. From an engineering and naval architecture perspective the conversion would be very difficult.
Submarines moving underwater need to be balanced along 3 axes. This complicates sub interior design. You want the large heavy items close to the centre of gravity for stability. If you move heavy items around you upset the balance. You then need to move the location of ballast and trim tanks to compensate, plus all the piping and pumps associated with them. Its a big job.
So unless the SMR and former diesel are a close match in size and mass, its hard. The French had exactly this problem with the Attack class.
Looks like Hyundai is also making non-nuclear inroads into Portugal:
"HD Hyundai Heavy Industries has signed an agreement with the Portuguese
Navy to explore the joint development of futuristic small submarines.
Signed at the recent Marine Defense Exhibition 2025 (MADEX) in Singapore,
the agreement is part of a potential strategic partnership that includes ship
maintenance, repair, and overhaul, according to South Korean daily Chosun."
See:
https://thedefensepost.com/2025/06/02/hd-hyundai-portuguese-navy/
Hi Anonymous at 6/03/2025 1:34 PM
I agree.
All the electricals and electronics (including sensors) vary between SSKs and SSNs. eg. the SSN's bow sonar is much more powerful and would have a different database as well.
Also SSNs travel much faster underwater and would have far different seafloor drive oceanography settings.
All this was to amount to a 15 year redesign transforming the Barracuda SSN into the Attack SSK.
Cheers Pete
Hi Anonymous at 6/04/2025 2:05 AM
Hyundai may be benefitting from South Korea's old Dolgorae-class midget submarine experience https://en.wikipedia.org/wiki/Dolgorae-class_submarine.
SK's three Dolgoraes, in commission 1985–2016 displaced 175 tonnes. I'm guessing the Italians (longterm users or mini-subs and diver delivery vehicles) helped SK in the design.
Cheers Pete
Hi
Couple of comments:
First the term SMR (Small Modular Reactor) typically refers to reactors that are small in comparison to gigawatt size traditional nuclear power plants. At 300 MWe they are still several times larger than traditional submarine reactors.
Second, I agree that nuclear submarines are quite different beasts that conventional submarines and it is not easy to convert one to the other. Another option is the nuclear AIP - a very small reactor that can provide hotel load and cruise capability to a conventional submarine. This might replace some but not all of the diesel engines.
A couple of years ago I mentioned that back in that late 1980's in Canada there was discussion of an Autonomous Marine Power Source (AMPS) for submarines. Initially proposed as a 100kWe system (1.5MW thermal) a later version known as AMPS 1000 had a projected capacity of 1700 kWe in cold water or 1300 kWe in 30C water. The AMPS 1000 was designed to fit in a neutral bouyancy plug about 10 metres long and at least 7.3 metres in diameter.
The 100 kWe AMPS gives the equivalent of a fuel cell or stirling AIP without the need to carry fuel or oxidizer, while the APMS 1000 would allow a submarine to complete an entire patrol without surfacing or snorkeling. It was also initially designed to be added to an existing conventional submarine.
AMPS has a number of disadvantages as well. The project never gained traction and a lot of work would have to be done again, the design uses rotating machinery so you may loose the extreme silence found in conventional submarines, and while it allows creep and cruising on nuclear power it does not allow high speed transits like a conventional SSN, which may be an Australian requirement.
More details on AMPS can be found at:
https://inis-temp.iaea.org/search/search.aspx?orig_q=RN:27015817
Another possibility is the Rolls Royce micro-reactor:
https://www.rolls-royce.com/innovation/novel-nuclear/micro-reactor.aspx
While AMPS is old technology the Rolls Royce micro-reactor is still under development, but it could provide similar power levels in a more modern package. Rolls Royce has the advantage that they have experience building submarine reactors, including silencing.
Hi Bill at 6/05/2025 1:52 PM
"nuclear AIP - a very small reactor that can provide hotel load and cruise capability to a conventional submarine. This might replace some but not all of the diesel engines." has long been theorised but remains unimplemented in subs.
Part reason may be - Why go to the trouble of having a complex micro-reactor + diesel hybrid when full PWR has the major advantages of driving SSNs at 35 knots and SSBNs at 25. Such speeds provide offensive as well as defensive (escape threats) advantages.
Cheers Pete
Nuclear AIP may indeed give you all of the disadvantages of an SSN with only a few of the advantages.
I guess the question is what is the RAN looking for from an AUKUS SSN? Fast transits? Time on station? Low indiscretion rate? And when dies the RAN need it?
Availability of a traditional SSN reactor may be the bottleneck for Australian SSN production. I have no idea on how long it would take to develop a nuclear AIP system but it might be the only option to meet the Australian timeline.
Personally I like the idea of buying Korean built KSIII but I understand that is not politically viable.
Hyundai's also done other work on minisubs:
"A few years before the decision to build the HDS-400, Hyundai unveiled the
stunning HDS-500 midget submarine concept. The futuristic design featured
a distinct streamlines sail and 'X' form tail mounted behind an integrated
pumpjet. Less obvious innovations include a mini wet-dry hangar in the tail."
Source:
http://www.hisutton.com/HDS-400_Midget-Submarine.html
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