09III/09IV (093/094) Nuclear Submarine Thread

[BoraTas]

5. natural circulation is important but I would also include that in an overall category of "nuclear reactor design quietening" which may require a "quieter reactor" to be larger in volume compared to a "louder reactor" of the same output

There are quite a number of comments on the internet by insiders that claim natural circulation mode is rarely used nowadays. Apparently, pumps are very quiet nowadays. The catch is, though, a reactor that is capable of running on natural circulation would have optimized fluid flow paths. Having such fluid flow paths is a quietening measure on its own regardless of whether you are going to run the reactor in natural circulation mode or not. So bigger is probably better indeed. Size should allow more gradual curves and bigger pipes.

I would guess that everything in a contemporary sub that involves fluid flows would have a lot of fluid dynamics trickery ongoing to keep the pumps and flows quiet. Here is a trick for rotary pumps from the civilian world. Such suction diffusers are used on civilian nuclear reactors too.

 

[latenlazy]

There is quite a number of comments on the internet by insiders that claim natural circulation mode is rarely used nowadays. Apparently, pumps are very quiet nowadays. The catch is though, a reactor that is capable of running on natural circulation would have optimized fluid flow paths. Having such fluid flow paths is a quietening measure on its own regardless of if you are going to run the reactor in natural circulation mode. So bigger is probably better indeed. Size should allow more gradual curves and bigger pipes.

I would guess that everything in a contemporary sub that involves fluid flows would have a lot of fluid dynamics trickery ongoing to keep the pumps and flows quiet. Here is a trick for rotary pumps from the civilian world. Such suction diffusers are used on civilian nuclear reactors too
View attachment 135972
View attachment 135974

Tbh designing natural circulation should be a lot easier today than in the past since complex fluidic dynamic modeling, especially of corner cases and flow states under complicated conditions, is much more advanced now than it was 40 years ago. You can probably even design a system that still employs pumps and valves but uses them only very selectively.

 

[AndrewS]

the size of pressure hull mainly just affects 2 and 3 in your list. More space inside -> more space to isolate noise generating parts.

Once you've rafted an entire internal section (like we see with photos of the Yasen or Astute), then you only get one frequency being transmitted through the rafting mounts/springs.

Any additional rafting of components shouldn't make a difference to the vibrations being transmitted through solid material to the outer hull.

Then you've got noise being transmitted through the air from components. I would expect most of that to be absorbed by the anechoic tiles on the hull, although they might add in additional acoustic insulation/foam around particularly noisy components. But I don't this taking that much useful additional internal space.

Precision machineries is to get all this stuff that spins to be quieter.

Precision shouldn't make a difference to anything that spins.

Arguably you want to spin things faster, as higher frequencies dissipate and get absorbed easier than low-frequency vibrations which travel further. That means smaller fans, motors and pumps.

But the big exception to this would be the propellor (and connecting drivetrain) which is in direct contact with the ocean. So you want these to spin slowly and smoothly, so it does help for them to be as precise as possible.

 

[BoraTas]

Precision shouldn't make a difference to anything that spins.

Arguably you want to spin things faster, as higher frequencies dissipate and get absorbed easier than low-frequency vibrations which travel further. That means smaller fans, motors and pumps.

But the big exception to this would be the propellor (and connecting drivetrain) which is in direct contact with the ocean. So you want these to spin slowly and smoothly, so it does help for them to be as precise as possible.

Completely completely outside what is being practiced. RPM and noise have a log-linear relationship. You add ~15 dB every time you double the RPM. Furthermore, noises by rotating machinery aren't single frequency noises. There is a good article here on fan noise.

Please, Log in or Register to view URLs content!

I advise you to not make confident claims against what is being practiced.

 

[drowingfish]

People don't think about availability long enough when it comes to submarine usage

The latest out of UK is a bunch of subs that never leave the port

Please, Log in or Register to view URLs content!

America has 37% of its nuclear submarine fleet in the port undeployable last year. And this will continue to get worse as the fleet ages and are asked to do long deployment.

As I said before, the number of subs America has at disposal for Westpac at any given time to do missions is probably not that many. And some of them I would imagine be used to track Chinese conventional fleet.

So that's why this is the decade when underwater balance of power might really change.

first you need those mini-nukes because then your lower cost fleet can spend more time at sea and need to be dealt with.

Then you can as many attack subs sailing around as possible so they can get more time outside of first island chain.

It is one thing to have 7 subs and only 1 or 2 can leave the port at a time. It's quite another thing to have 25 and 8 of them are out at patrol.

when do you think PLAN can get to 25? that is quite a significant number...

 

[tphuang]

Tbh designing natural circulation should be a lot easier today than in the past since complex fluidic dynamic modeling, especially of corner cases and flow states under complicated conditions, is much more advanced now than it was 40 years ago. You can probably even design a system that still employs pumps and valves but uses them only very selectively.

natural circulation isn't that important. You need it for high speed operations. But frankly, that's not where the noise comes from.

Neither is the reactor itself.

I think we had a discussion on this with diagram of propulsion system of LA class a while back. There is a lot of stuff that spins in there.

btw, that's also why nuclear electric is so much better technology. It's just electric drive rotating electric motor. much fewer turning parts. If anyone ever listened to a EV presentation, they always talk about just how quiet their cars are. Just a much better technology than purely nuclear driving a shaft.

 

[Blitzo]

natural circulation isn't that important. You need it for high speed operations.

I don't think this is the case.

My understanding is that for a nuclear submarine, natural circulation can be attained to a fraction of a nuclear submarine's reactor maximum output, however at greater output (and higher speeds), they need forced pumping to occur as well, which presents a source of noise.

Being able to design a reactor that can achieve greater fractions of its full output on natural circulation is thus desirable of course, because being able to attain higher speed without using active pumping of coolant is preferred. If you didn't have natural circulation at all then you have to use your active pumping constantly.

So it's not the case that natural circulation is "needed" for high speed operations, rather that natural circulation is usable at certain lower speeds and at higher speeds you'll probably be turning on your active pumps.


As for the noise of a reactor, trivializing it as a source of noise probably shouldn't be said so casually. It should better be said that reactors can be feasibly designed to produce lower noise, however that wasn't always the case for the PRC.
For example, a reactor without natural circulation at all means its pumps will be always needed to circulate coolant, so yes natural circulation is absolutely important compared to a reactor which lacks natural circulation.

I think we had a discussion on this with diagram of propulsion system of LA class a while back. There is a lot of stuff that spins in there.

btw, that's also why nuclear electric is so much better technology. It's just electric drive rotating electric motor. much fewer turning parts. If anyone ever listened to a EV presentation, they always talk about just how quiet their cars are. Just a much better technology than purely nuclear driving a shaft.

Electric propulsion certainly looks like the next more widespread evolution of nuclear submarine propulsion, being able to remove the reduction gearings from drivetrain, which is indeed a source of noise.

But the reactor itself shouldn't be trivialized as a source of noise either, especially for the PLAN, who are still relatively new to proving their mettle at sufficiently high output submarine nuclear reactors that can also be low noise.

 

[tphuang]

I don't think this is the case.

My understanding is that for a nuclear submarine, natural circulation can be attained to a fraction of a nuclear submarine's reactor maximum output, however at greater output (and higher speeds), they need forced pumping to occur as well, which presents a source of noise.

Being able to design a reactor that can achieve greater fractions of its full output on natural circulation is thus desirable of course, because being able to attain higher speed without using active pumping of coolant is preferred. If you didn't have natural circulation at all then you have to use your active pumping constantly.

So it's not the case that natural circulation is "needed" for high speed operations, rather that natural circulation is usable at certain lower speeds and at higher speeds you'll probably be turning on your active pumps.


As for the noise of a reactor, trivializing it as a source of noise probably shouldn't be said so casually. It should better be said that reactors can be feasibly designed to produce lower noise, however that wasn't always the case for the PRC.
For example, a reactor without natural circulation at all means its pumps will be always needed to circulate coolant, so yes natural circulation is absolutely important compared to a reactor which lacks natural circulation.



Electric propulsion certainly looks like the next more widespread evolution of nuclear submarine propulsion, being able to remove the reduction gearings from drivetrain, which is indeed a source of noise.

But the reactor itself shouldn't be trivialized as a source of noise either, especially for the PLAN, who are still relatively new to proving their mettle at sufficiently high output submarine nuclear reactors that can also be low noise.

Now I re-read what I wrote and it makes no sense. I meant to say you cannot use natural circulation at those highest speed that your attack subs would need to go sometimes.

As for coolant pumps, my understanding is that it's also in the engine room next to the steam generator. So just one of the many items your passive noise absorbers need to handle.

I have not seen too many places that said reactor itself (not the coolant pumps) is a major noise generator. See HI Sutton piece here

Please, Log in or Register to view URLs content!

Originally only the propulsion and noisy machinery was raft mounted, and on some submarines this had to be locked in place during high speed operations. Nowadays in some designs whole deck modules are raft mounted, even in the accommodation and control spaces:

Doesn't seem to me the reactor itself needs to be raft mounted. Although, it looks like the control spaces and living quarters are even mounted now so that all the noise from machines gets absorbed also.

 

[tphuang]

it dawned on me that we are finally seeing Chinese submarines expanding because the domestic industries are ready for it.

As seen here with the Royal Navy, all that fancy submarines can't leave the dock due to lack of domestic industries to support them.

Please, Log in or Register to view URLs content!

So if you ramp up production of nuclear submarines, you need the entire upstream supply chain for nuclear, which they have just recently built. They have also just recently gotten to the next level on precision manufacturing and material science. All things they didn't really have 10 years ago.

 

[snake65]

So if you ramp up production of nuclear submarines, you need the entire upstream supply chain for nuclear, which they have just recently built. They have also just recently gotten to the next level on precision manufacturing and material science. All things they didn't really have 10 years ago.

The last two are the biggest plague of most of the Western Navies.

The area that has been most affected in infrastructure, spares, maintenance, training and manpower.