Pondering an approach to nuclear submarines for Sweden

[Micael]

So traditionally nuclear submarines tends to cost a whole lot, and tends to need to be fairly large, or as in the case of the French Rubis class which isn’t as large there tends to be some associated drawbacks.

I have been pondering a bit if there could be a feasible way that Sweden could acquire nuclear submarines, a way that isn’t quite as expensive and would still be practical. Since there is a Swedish company that is now working on bringing an SMR design to the commercial market it was a natural place to start my ponderings. Blykalla has designed an SMR caller SEALER-55. It uses lead cooling, as we’ve seen in some submarine reactor designs of the past, but it seems that they’ve managed to crack the big issue of those past designs with the lead corroding the materials around it, by developing new alloys that isn’t affected by this. The reactor also operates at one atmosphere and thus doesn’t require nearly as substantial of a reactor vessel as pressurized designs. Generating 55 MW is has a footprint of 5x5 meters. This output is slightly higher than in the French Rubis class (48 MW) and a bit more than a third of the 150 MW more common in SSNs. Blykalla is also in partnerships exploiting the design for commercial maritime transport and seem confident that there’s no inherent issue that prevents the design from being mounted in a moving vessel. The reactor fuel used is uranium nitride and it allows for 25 years of operation without refuelling in commercial operation, I would imagine a bit longer given the operating cycle of a submarine. (The French have, being a bit contrarian to others, opted for low enriched fuel in their latest classes which forces a refuelling every ten years.)

If plans come true in which Blykalla manages to establish mass production of the design by the early 2030’s (we shall see), it should also be comparatively inexpensive compared to the traditional submarine reactors. Conceivably you could use it in a small SSN design (such as the Rubis), or fit 2-3 of the reactors in a larger design. Being a completely passively safe design it would also avoid some of the issues with regards to the public, ie convincing them that there isn’t a safety concern with it.

Does anyone have any thoughts on this? If there are any major issues with this idea?

[Pdf27]

Lots. That sounds very big for a submarine reactor, and it will have serious issues with 135-Xe poisoning when changing power. Silencing the rest of the plant is non-trivial, and the benefits of a nuclear plant in the Baltic are very minimal.

[Micael]

Lots. That sounds very big for a submarine reactor, and it will have serious issues with 135-Xe poisoning when changing power. Silencing the rest of the plant is non-trivial, and the benefits of a nuclear plant in the Baltic are very minimal.

Well the size includes the external housing for land based emplacements, I’m assuming that incorporating it inside a hull could be done as the reactor itself would be smaller than the cubical footprint. The 135-Xe poisoning bit is very interesting, so you think that it’ll have more issues with that than a ”traditional” BWR? I’m wondering how Blykalla is planning to make the commercial maritime use happen then as it should also have to change power a fair bit. The silencing, well yes, but that’s a problem that can be overcome with enough work. I’m not primarily thinking the Baltic here, for that the Sterling AIP works well enough. I’m more thinking ahead to potentially operating nuclear launch systems and putting them out towards the North Sea.

[Pdf27]

The issue is that civil reactors just accept that 135-Xe poisoning is a thing and live with the time constant (France for instance manages this with vast amounts of hydropower). Nuclear submarine reactors can't accept that, so they're designed from the start with much more neutron flux available. Using lead/lead-bismuth eutectic cooling isn't an inherent problem (the Soviets built a number of submarines using this), but it requires a massive redesign.

Cargo ships are much easier - they're only going to go to low power in port where tugs are available, and nuclear propulsion is only really of interest for long distance voyages which will have enough loading/unloading time to climb out of the pit again. I suspect they're mainly included for the pitch deck to investors as well - compared to static SMR applications the paperwork for a cargo vessel will be deeply painful.

[Nathan45]

Micael, are you thinking that long term the Swedish navy would benefit from developing the infrastructure for nuclear propulsion, regardless of the difficulties in the short term? I can see the need for that, with the USN no longer looking like a reliable ally and the security situation with Russia being what it is. In practical terms, what are the advantages and disadvantages of nuclear power in the region?

[Micael]

Micael, are you thinking that long term the Swedish navy would benefit from developing the infrastructure for nuclear propulsion, regardless of the difficulties in the short term? I can see the need for that, with the USN no longer looking like a reliable ally and the security situation with Russia being what it is. In practical terms, what are the advantages and disadvantages of nuclear power in the region?

Yes essentially like that, but of course if we could leverage some civilian project like SEALER-55 to keep the costs more reasonable for a small country that would be preferable as we have a lot of other military things that we need to spend money on.

If we look at the Baltic Sea first, which have traditionally been our area of highest interest, for the most part the cons outweigh the pros with regards to nuclear propulsion. The submarines have to be of a size that makes it problematic for them to operate efficiently in the tight and shallow sea. They won’t be able to go in many places that a smaller conventional submarine can. AIP propulsion is also sufficiently advanced now to give enough underwater endurance for that area of operations.

If we look to the North Sea however the calculation changes a bit. While you can operate there with conventional submarines the nuclear ones have significant advantages in terms of extended endurance at sea, higher speeds if you for instance need to hunt down a Russian submarine (and not just wait for it to come to you.) Then we have that issue with potential nuclear weapons capability. If we were to acquire that it would, at least in the slightly longer perspective, be preferable if we could add a submarine launched capability to that. While it is possible to have even ballistic missiles on a conventional submarine (see Soviet Golf-class), and it appears that the new A26 could fit at least three Trident-sized tubes with a hull plug (or 18 Tomahawk sized tubes), it is clear that a nuclear powered one would be much better for that particular role. Perhaps not necessarily as large as some others, but the nuclear propulsion would still be key to lenghty hide and seek sessions in deep waters.

[Craiglxviii]

Stuart wrote an interesting essay on exactly this. The problems with adopting nuclear-powered vessels. I’ll see if I can find it.

[kdahm]

If we look to the North Sea however the calculation changes a bit. While you can operate there with conventional submarines the nuclear ones have significant advantages in terms of extended endurance at sea, higher speeds if you for instance need to hunt down a Russian submarine (and not just wait for it to come to you.) Then we have that issue with potential nuclear weapons capability. If we were to acquire that it would, at least in the slightly longer perspective, be preferable if we could add a submarine launched capability to that. While it is possible to have even ballistic missiles on a conventional submarine (see Soviet Golf-class), and it appears that the new A26 could fit at least three Trident-sized tubes with a hull plug (or 18 Tomahawk sized tubes), it is clear that a nuclear powered one would be much better for that particular role. Perhaps not necessarily as large as some others, but the nuclear propulsion would still be key to lenghty hide and seek sessions in deep waters.

I don't think the calculus changes that much, depending on what your submarine is intended to do. For a SSB or SSBN, nuclear is clearly superior because it allows for very long patrols, longer and quieter transits, and better launch spots. Also, the subs would not be limited to just the North Sea. And since these are very expensive, the best choice may be to simply buy into the British SSBN program.

For hunter/killer subs, I think the best choice would still be conventional AIP instead of nuclear. There's a significant cost and size increase for nuclear. Transits for Sweden in the North Sea and along the Norwegian coast are around 300-750 nm, easily within the capabilities of conventional subs, and there are plenty of friendly bases all around. From a design standpoint, a Baltic design and a North Sea design could be almost identical, with the latter having some hull plugs. I think the key question is endurance, and whether Sweden wants or needs to have subs that can stay away from port for more than three weeks or a month at a time.

[Craiglxviii]

Here is the essay.

Worth a read… it should answer may od the questions raised in this thread.

https://tboverse.com/viewtopic.php?p=50 ... bis#p50782