Rumoured "mini-nuke/diesel" Submarine SSK-N(?) thread

[obj 705A]

This new submarine may be a test vessel for an upgrade of all AIP Type 039A/B/C which will be done the same way as the modernisation of Vastergotland SSKs in 2003-4 when they received the AIP module designed for Gotland. The test vessel for AIP was the previous class Nacken, refit in 1987.

If Sweden managed to upgrade two subs in two years then with 20 039s in Service PLAN could gain 20 new SSNs within 5 years at 4x the Swedish workload which should be easily achievable at Wuchang. And if the mini-reactor module is well designed all of the infrastructure is already in place. Nothing Huludao can do would match it in terms of quantum leap/paradigm shift shock to the system.

Well who knows maybe they would indeed upgrade existing SSKs with a nuclear reactor but IMO that sounds unlikely.

it would be much easier to just build brand new SSKNs than to upgrade existing ones.

 

[FairAndUnbiased]

The Stirling engine that was developed for 039B/C subs had 320kW power @ 40% efficiency. That's really pretty weak for this scenario.

No because you have to compare it to diesel and combustion Stirlings.

Gotland uses 2x 100 kW Stirling. Kilo is 1 MW diesel. 6x 320 kW is huge for a SSK sized sub. 40% efficiency is pretty good for a heat engine.

 

[tphuang]

No because you have to compare it to diesel and combustion Stirlings.

Gotland uses 2x 100 kW Stirling. Kilo is 1 MW diesel. 6x 320 kW is huge for a SSK sized sub. 40% efficiency is pretty good for a heat engine.

6x320kW might be fine for SSK sized sub, but how do we know they can fit 6 in a Yuan sized sub? The current Yuan fits in 1.

And also Yuan transits in PD, because going at lower depth even at low speed will use up its battery pretty quickly.

If we are doing the heavy lifting of putting nuclear reactor in there, 2 MWt of power seems insufficient.

Of course, if you just want it to ambush, it can do that.

but if you are doing the hard work of fitting nuclear reactor in there, you probably want it to be able to transit at harder to detect depth and also be able to move faster for longer duration in emergency situations.

Also, there is the additional headache of ventilation. nuclear subs has these atmosphere control equipment which removes the need for submarine to come up to ventilate. You would need more power than 2MW to support something like that in a mini-nuke

 

[Blitzo]

There is no reason for it to be less stealthy. If anything it could be stealthier than conventional SSK. It has unlimited battery for stealth. Besides noiss, it needs little radiation insulation because slide said it has comparable radiation to level conventional subs. Its size is SSK level. Its speed is not an issue because it can just mobe slower if needed. I think its stealth advantage over full sized nuclear sub is pretty solid. Possibly even better than SSK.

I never said that the "SSKN" will be less stealthy than a proper SSN, I said that in open ocean environments where speed matters more than littoral environments, the SSKN is likely to be inferior to a proper SSN.

Speed is absolutely vital for the missions that proper ocean going SSNs are expected to do; speed determines their ability to ingress and egress out of situations as well as the ability to outrun ASW search screens (whether it be surface or air).

SSKN is not invincible, it cannot solo the enemy without support. But I am certain all else equal it is much safer than other sub types. The only limiting factor is its weaker offensive armament, but that is outside its mission profile. It is like complaing F-22 cannot replace B-52.

Don't use a strawman -- I never accused you of saying that the "SSKN" is invincible.

What I am contesting is what you wrote here: "Not just the endurance, it will perform the role of nuclear attack subs exponentially better." -- I am saying that the SSKN will do a very different role of a nuclear attack submarine, so they cannot be compared.
If you were to force a SSKN to do the role of a proper nuclear attack submarine, it will be much worse.


If you agree that a SSKN is unable to do the role of a nuclear attack submarine exponentially better and if you agree that the SSKN is likely to be much worse at the role of a nuclear attack submarine, then we have no problems.

Despite sharing similar dimensions and hopefully cost to modern SSKs, the SSKN is a “true” SSN. It has a nuclear reactor that gives unlimited range and endurance at tactically significant speed.

Of the four inferiorities you listed, only the slower top speed is inherently true for the SSKN. The rest are not so much about SSKN vs. “true” SSNs but about smaller vs larger SSN.

SSNs grew to its current size for many reasons but perhaps the most crucial one is that larger hull diameter allows for more quieting equipment and better natural circulation reactors. This makes larger SSNs quieter than smaller SSN given the same technological level. The small low powered reactor+Sterling engine+battery+turboelectric drive design allows small SSN to be just as quiet if not more so.

Is a small SSN that trade top sustained speed for cost a good investment for a country whose primary threat have extensive naval presence with 1000nm, whose geography is surrounded by maritime choke points that demands continuous presence, and who already has extensive infrastructure sustaining 2-3000t class submarines? Absolutely yes.

The usefulness of the SSKN (if it's real) for the PLAN is not something I'm contesting.

I am challenging and outright denying the idea that a "SSKN" is able to take on the mission (let alone do it "exponentially better") than a proper nuclear attack submarine.


This SSKN discussion and platform is emerging into the scene where the role and mission profile of a nuclear submarine is already fairly well established, so yes the SSKN will have to be compared with what proper nuclear attack submarines are able to do, including perishables endurance, weapon and sensor loads, and most importantly transit and tactical speeds.

 

[Rank Amateur]

"You also need the transmission gearbox to be able to change gears for different speed conditions."

-> No, the sub does not shift gears.

OK got it, so speed changes by reducing output? That means a throttleable reactor.

I looked into the matter, and it appears that in the kind of sub the illustration of which you attached, shaft/propeller speed is changed by increasing or decreasing the steam flow into the turbines. There's a significant degree of self-regulation, in that flowing more/less steam inherently causes the reactor to generate more/less power until an equilibrium is reached at the new speed setting. Major speed changes might require some adjustment of the control rods, though.

Note that all of the above came from some quick online research. If I got anything wrong, I welcome correction.

 

[antiterror13]

Is there any rumours whether this SSK-N would be single or double hull?

 

[FairAndUnbiased]

6x320kW might be fine for SSK sized sub, but how do we know they can fit 6 in a Yuan sized sub? The current Yuan fits in 1.

And also Yuan transits in PD, because going at lower depth even at low speed will use up its battery pretty quickly.

If we are doing the heavy lifting of putting nuclear reactor in there, 2 MWt of power seems insufficient.

Of course, if you just want it to ambush, it can do that.

but if you are doing the hard work of fitting nuclear reactor in there, you probably want it to be able to transit at harder to detect depth and also be able to move faster for longer duration in emergency situations.

Also, there is the additional headache of ventilation. nuclear subs has these atmosphere control equipment which removes the need for submarine to come up to ventilate. You would need more power than 2MW to support something like that in a mini-nuke

But you also don't need fuel tanks or exhaust management system for it. The Stirling engine itself is tiny.

What takes up room would be the fuel tanks, the exhaust management, etc. The reason subs usually have 1x or 2x is not because they can't fit another Stirling engine, it is because they don't have the fuel to actually use it effectively.

But if you only have a high temperature heat exchanger leading up to it with no need for exhaust management or fuel, then you can just stack them.

 

[tphuang]

But you also don't need fuel tanks or exhaust management system for it. The Stirling engine itself is tiny.

What takes up room would be the fuel tanks, the exhaust management, etc. The reason subs usually have 1x or 2x is not because they can't fit another Stirling engine, it is because they don't have the fuel to actually use it effectively.

But if you only have a high temperature heat exchanger leading up to it with no need for exhaust management or fuel, then you can just stack them.

Stirling engine makes a lot of noise. China has to put significant raft mounting around Yuan's Stirling engine to keep the noise from getting out. Have 6 of them will require a pretty large sized rafting. Yuan's inner hull isn't that spacious.

And that's if you are satisfied with just 2 MWt in power. Which in my opinion is not enough. If you are getting mini-Nuke, you want it to be a lot higher than that.

 

[FairAndUnbiased]

Stirling engine makes a lot of noise. China has to put significant raft mounting around Yuan's Stirling engine to keep the noise from getting out. Have 6 of them will require a pretty large sized rafting. Yuan's inner hull isn't that spacious.

And that's if you are satisfied with just 2 MWt in power. Which in my opinion is not enough. If you are getting mini-Nuke, you want it to be a lot higher than that.

Compared to what?

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"The Stirling engine is quiet and vibration free. No vibrations spread out to the hull making the submarine silent in the water and therefore difficult to find. This technology is unique to Swedish submarines" remarks Sebastian Lenander, Manager, Assembly and Testing Stirling, Saab Kockums.

Unless China's mechanical engineering is just absolute shit compared to Sweden's, which I find difficult to believe seeing that China has a space program, lithography, EV program, etc all heavily dependent on mechanical engineering, and Sweden doesn't, the general principle should apply too.

The whole point of using a Stirling engine is for the noise reduction. Otherwise why not just fire up the diesel underwater and use a LOX regasifier, why doesn't anyone do that and go through the trouble of using a Stirling? How come nobody uses the French turbine AIP and everyone either uses fuel cell or Stirling? It definitely isn't for the power.

 

[tphuang]

Compared to what?

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Unless China's mechanical engineering is just absolute shit compared to Sweden's, which I find difficult to believe seeing that China has a space program, lithography, EV program, etc all heavily dependent on mechanical engineering, and Sweden doesn't, the general principle should apply too.

The whole point of using a Stirling engine is for the noise reduction. Otherwise why not just fire up the diesel underwater and use a LOX regasifier, why doesn't anyone do that and go through the trouble of using a Stirling? How come nobody uses the French turbine AIP and everyone either uses fuel cell or Stirling? It definitely isn't for the power.

compared to battery electric. I've spoken to submariners on this topic. How can you put a combustion engine in a submarine and expect it to be quieter than battery? You need to isolate the noise produced by Stirling.

Isolating 1 Stirling vs 6 requires entirely different size of rafting. Again, 2MW is not sufficient.

Stirling to me seems like it's for some very lower powered applications and not ideal for steam generator of a nuclear reactor