They do still need nuclear engineers and technicians to operate the small nuclear reactor onboard the 04X SSK-N.
Rumoured "mini-nuke/diesel" Submarine SSK-N(?) thread
- Thread starter ACuriousPLAFan
- Start date
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.
on the other hand, you need a whole lot of isolation around reactor and engine. If you task a sub with more capability like moving along at lower depth, it's going to produce more noise too.
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.
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.
you wouldn't use sterling engine if you have a reactor. you'd want to eliminate all the diesel/ICE related stuff and just go with battery and have nuclear reactor generate electricity which with power the boat. rather than having nuclear reactor power the shaft.
I'd actually be curious what how much noise gets generated in this case.
you don't need coolant pump or reduction gear or shaft.
with my very rudimentary understanding of nuclear reactor, the steam generator & turbine is what generates the electricity. So that i would imagine can get quite noisy (just have turbine rotating would make noise), but since you don't have requirement for 30 knots, the steam engine would be much less powerful.
Maybe 20MWt vs 200MWt (like on OK-650). I don't know how much less noise would be made when output is reduce by a magnitude.
take a look at what actually takes up room.
Let me point a few things out:
1. the reactor space is not the only space taken up by the propulsion system. Notice that the reactor is connected to a steam generator, which connects to a turbine, which turns a shaft. The shaft is connected both to a generator and drives the propellers.
2. The problem is, a generator shaft spins fast, but a propeller spins slow. That means you need a transmission gearbox to turn the fast spinning low torque generator shaft to the slow but high torque propeller speed. You also need the transmission gearbox to be able to change gears for different speed conditions.
3. The shaft is straight. You can't bend it or change its direction. All that takes up room. You need significant clearance around the moving shaft and gearboxes for maintenance, as they're moving parts. Thus, a direct drive engine actually takes up a huge amount of space with the heat exchanger, steam generator, turbine, generator, turbine, etc and their associated engineering spaces.
Let me point out how big and complicated a steam generator is. Diagram to show complexity, then a photo to show size.
Just a minor correction.
"The problem is, a generator shaft spins fast, but a propeller spins slow. That means you need a transmission gearbox to turn the fast spinning low torque generator shaft to the slow but high torque propeller speed."
-> Yes, referred to as the "reduction" gearing.
"You also need the transmission gearbox to be able to change gears for different speed conditions."
-> No, the sub does not shift gears.
Such behaviour explicitly breaks rules of this forum:
It also shows lack of common courtesy to users who don't know Mandarin sufficiently well to understand it without help of translators.
Personally I am very much in favour of providing, whenever possible, the original text in a format that allows users to copy it and use translation, since that helps both with interpretation of the text and also familiarisation with the language. If popularising knowledge about PLA is the forum's primary purpose then popularising the use of Mandarin sources should be the secondary one. I also think that people who know Mandarin should feel obliged to do their part in popularising use of Mandarin. Otherwise they're just pests breaking the rules, littering the forum with useless posts and contributing nothing of real social value.
Confucius says quite a lot but none of it is polite language. Don't disappoint Confucius by choosing to be self-important pests. Instead make Confucius proud by choosing to follow proper rules of conduct and being socially useful.
Anyway, that's not why I'm posting here.
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On the rumoured new submarine:
First of all it is not a hybrid nuclear-conventional submarine. It is a nuclear submarine. Not an "SSN-K" or "SSK-N" but an SSN. A low-performance SSN is still an SSN. An SSN with operational and tactical profile of an SSK is still an SSN.
What makes a conventional submarine "conventional" is not the electric batteries but a combustion engine as the energy source. What makes a nuclear submarine "nuclear" is not its speed but a nuclear reactor as the energy source. There is nothing that suggests that a nuclear submarine has to operate at high speeds for long periods of time since most of the time SSNs operate at low and very low speeds. They only use sustained high speeds in emergencies.
Nuclear-powered submarines were invented when a 3000t SSK like Kilo on battery power had a maximum range 750 km at 3 knots or energy reserve of about a week. At maximum speed of 20 knots Kilo has range of 70km if I remember correctly.
Those numbers are why nuclear propulsion was revolutionary. All the other capabilities like being able to move thousands of kms under ice or spend weeks within enemy waters only came later - 10 to 20 years after Nautilus first went to sea. If you want to understand any innovation you have to understand it in its immediate context - what the innovators wanted to achieve at the time, and not what the technology allows for one or two decades after introduction.
Secondly there is nothing unusual about combining a 10MW reactor and 1,3MW quadruple Stirling unit in an experimental submarine.
10MW is very low power output for a naval reactor and at the same time too much for a SSK and not enough for a traditional SSN. Rubis which had comparable size (2600t / 73m x 7,6m) had 48MW of peak reactor power producing maximum speed of 25 knots. At 1/5 of that this new Chinese SSN with a steam turbine would have never been able to move faster than 10 knots. The loss of energy would be too great.
Instead the reactor is likely going to power an electric motor in a non-linear arrangement which will propel the submarine indirectly and charge the batteries. This way the submarine will have all the advantages of modern SSKs as well as avoid the noisy turbine-propeller shaft, with none of the disadvantages.
10MW is likely peak power that allows for large variability in power output while most likely using LEU as fuel. LEU reactors are very inefficient per fuel mass which could mean that 10MW is achieved when the reactor uses up all its fuel while during standard operations it uses as little as 2-3MW or perhaps even less. This way the reactor.
The Stirling engines likely fulfill two functions:
- They serve as a backup since it's an experimental submarine that will be used to develop completely new operating procedures - there is no way to explore the possibilities without risk.
- They serve as secondary source of energy for charging of batteries when the sub runs on maximum reactor power due to inefficiency of the turbine/motor.
Gotland (1600t / 60m x 6,4m) is powered by two United Stirling AB V4-275R engines rated at 100kW each which allows for sustaining of maximum of 5 knots or recharging batteries. 4x320 is 6x what Gotland has and Gotlands operate regularly for days while using Stirling as main power source. Also it can operate on just a single Stirling engine. The second one is a backup.
Kilo (3100t / 73m x 9,9m) has two 1 MW diesel generators and one 5 MW electric motor. This way Kilo can discharge a lot of stored energy (measured in kWh) in short amount of time to reach 20 knots on batteries but at limited range (see above). Under snorkel it can only generate 2 MW of power to move at 17 knots and slowly recharge batteries at the same time.
At 1,3MW the new sub is at 60% of Kilo which makes it already that much more capable than the already capable Gotland. It is excessive.
Which leads me to believe that the purpose of this sub - or two subs to be precise - is to test the solution in practical conditions. I think the propulsion has been already tested and now it's going to be put to use in actual combat exercises or scenarios. I would even expect the power output of the mini-reactor and the Stirling unit to be greater than necessary precisely so that the submarine can test options for a hypothetical serial production.
For example - what is better: 6MW reactor + 4x 0,3MW Stirlings or 4MW reactor and 2x 0,3 Stirlings or perhaps 10MW reactor and 2x 0,3 Stirlings?
And here's my main thought:
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.
039 would also immediately become extremely attractive as an export offer considering that countries could buy a SSK and later upgrade to SSN. This is relevant for Pakistan as well as for basing of PLAN 039s in Pakistan.
Naturally I don't have the relevant numbers so I have to make somewhat-informed guesses but at first glance a "new 10MW SSN" doesn't make any sense for a country with the world's largest shipbuilding industry. Especially that in many aspects submarines benefit from the same economies of scale that affect carrier design - bigger is better. Why build small under-powered SSNs when you can build large properly-powered SSNs?
But it makes perfect sense when it's not about a new 10MW SSN but something more radical than that: a change in strategy. Anyone who has read Sun Tzu will know that it is best.
This is obviously just a speculation, but I wanted to put it to record. In terms of grand strategy fits China's needs too well, so who knows?
ANY engine that uses the Stirling thermodynamic cycle is a Stirling engine. It does not matter what the original source of the energy is whether it is burning cow dung or putting it in the sun or burning diesel or a reactor. It does not matter, only matters that there is a temperature gradient.
Why Stirling engine over turbine (Rankine engine)? I can think of many advantages such as less moving parts, no need for steam generation and regeneration, etc.
The only sound generated is metal against metal in a piston (minimal based on how quiet piston combustion engines have become) and the generator.
OK got it, so speed changes by reducing output? That means a throttleable reactor.
Based on my understanding, less. Stirling engine is a reciprocating engine, turbines are rotary.
A reciprocating engine can be very quiet since the only motion is 2 lubricated metal cylinders sliding past each other.
Turbine engines have 2 sources of noise: working fluid flowing over the rotor blades, and the shaft noise at resonances.
The Stirling engine that was developed for 039B/C subs had 320kW power @ 40% efficiency. That's really pretty weak for this scenario.