Let's join in the fun and talk about "baby killer whales".
In the past two days on the Internet, we have seen many people talking about "small nuclear fish, little killer whales", and some people even said that they have begun to build in batches in China. I don't have the ability to prove whether this kind of news is true or false, because a retired old man doesn't have that much official news. However, I can talk about whether the "Little Killer Whale" is necessary or not, and what major technological breakthroughs are needed to really make the "Little Killer Whale" have the advantage of actual combat.
First of all, whether it is a "small nuclear fish" or a "little killer whale", it first involves a question of definition. Is it all-nuclear, or is it AIP powered by partial nuclear power? There is an essential difference between these two.
AIP is essentially an auxiliary power, while all-nuclear power is the main power that uses nuclear power as the main power. So does AIP have a technical advantage, and how significant is it? I have a question mark on this question, because the power system of submarines is inherently complex.
The old conventional diesel-electric submarine, it actually has two sets of power systems, one is pure electric propulsion underwater, and the other is diesel engine power on the surface and snorkel. However, such a power composition involves the storage capacity of the battery, and the underwater endurance is greatly limited, and only later did AIP power appear. After the AIP power came up, it actually further complicated the conventionally powered submarine, which was equivalent to adding a new set of power units on the basis of the original diesel engine, battery, and motor. It doesn't matter if you're a fuel cell or a closed-cycle diesel engine, there's one more thing.
What is the result of having one more set of things? It is certain that the more complex the system, the greater the technical difficulty, the higher the failure rate, the higher the cost, and the problems brought by the traditional conventional AIP are not only in the boat itself, but also in the shore logistics support system of the submarine. In the past, you could supply oil, water, and electricity, but now you need liquid oxygen, and even liquid hydrogen, and liquid oxygen and liquid hydrogen are not easy to serve, and they are all flammable and explosive materials, which is not a small pressure on logistics.
However, under the urgent need for submarine underwater maneuverability, despite this cost, the navies of many countries have stubbornly taken the conventional AIP. Is regular AIP the best? Certainly not the best. For one, it is limited in its ability to sail underwater, in other words, it is limited by the liquid oxygen you carry. In addition, the cost is definitely a hard expenditure, which is not only a one-time investment, but also includes the cost of operation.
We saw that after Japan's conventional submarines replaced their lead-acid batteries with lithium batteries, they abandoned the AIP. Why did you make such a technical choice? Because after adding lithium battery, the battery's power storage capacity has been greatly increased, and the underwater navigation capacity is almost the same as that of AIP. Is it necessary to install AIP at this time? The choice made by Japan is to throw away the AIP, and it is enough to have lithium batteries. In fact, this choice makes sense, and in a sense, it is also wise. Submarines can't pile up indefinitely, indefinitely, and in the end there are always problems, either they are too expensive, they can't afford it, they can't afford it, or they have a highly complex system with frequent breakdowns.
So, when it comes to this place, it comes to the issue of "baby killer whales". What exactly is a "baby killer whale"? Is it a purely nuclear-powered small pile, or an AIP submarine with nuclear power as auxiliary power? In fact, there are problems with both paths now. Using nuclear power as auxiliary power is a bit more than worth the loss after a little pondering. The benefits of nuclear power are not fully obtained, because the heap is small and the power is low. However, there are no fewer problems with nuclear power, such as the need to shield radiation from the tonnage size problems, such as the feeding of nuclear fuel, the problem of overhaul in the factory, and the problem of reprocessing after decommissioning. If your small pile is a pressurized water reactor in the traditional sense, then none of these things are indispensable.
Then there is another way to define it, which is a purely nuclear-powered small nuclear submarine. This small is relative and more typical. You belong to this category of "Ruby"-class nuclear submarines like the French back then. It is a purely nuclear-powered, but the underwater displacement is only more than 2,700 tons, which is even smaller than the displacement of some conventionally powered submarines today.
So how did the French achieve this nuclear power for a dinghy? In fact, it is just a high degree of compression and miniaturization on the basis of pressurized water reactors, such as the integration of pressurized water reactors, and the entire primary circuit is compressed into a pressure shell. This brings two benefits, one is that the size is greatly reduced, and the second advantage is that the natural circulation ability is greatly enhanced. Natural circulation capacity has been strengthened, there is no need for circulation pumps, the complexity of the system has been reduced, and circulation pumps are one of the main sources of noise for nuclear submarines. By removing this noise source, the quietness can be improved a lot. We see that the most advanced nuclear submarines nowadays, when it comes to quiet sailing, often use the natural cycle method.
What about the faults, the faults are also a bunch, the pure natural circulation method, the power, volume-to-weight ratio of the entire system will be reduced, that is to say, the power that the nuclear submarine can output will be reduced. If the whole nuclear reactor is integrated, including the first circuit, then if your nuclear reactor wants to be refueled, it will be troublesome, and if there is a problem in the first circuit, it cannot be repaired, and if it is repaired, it will be overhauled, and the pressure shell of the reactor will be cut, which is a "major operation". So in the end, the French Navy only engaged in such a generation of small all-nuclear-powered submarines, and then abandoned this idea. Giving up means that you can't go on.
Speaking of this, everyone may say, you blocked the two roads of the "little killer whale", is it that the "little killer whale and small nuclear fish" are meaningless and have no technical possibility? In order to truly achieve an all-round "little killer whale", what do you need to do?
At least three things need to be done. First, the complexity of the system does not increase on a large scale, and even if it does, the ratio of benefits to benefits is negligible. Second, the cost is controllable, if the cost of "little killer whales" and "big nuclear fish" is completely in the same order of magnitude, then what is the meaning of "little killer whales", just you can directly engage in "big nuclear fish". The third is that the use of protection should not be too troublesome. Only when these three points are realized can "little killer whales and small nuclear fish" really become popular.
How can we achieve these three points? The key point is not to think about the problem according to the traditional PWR thinking. If the traditional pressurized water reactor is still used to engage in the so-called "small nuclear fish and small killer whales", it will basically enter a technological dead end. Therefore, the advent of "little killer whales and small nuclear fish" is based on an essential breakthrough in nuclear power plants. It is not a matter of changing the pressurized water reactor, shrinking it, or pressurizing it.
So what kind of technological breakthroughs are needed to make "little killer whales and small nuclear fish" attractive enough? I've told you about it before, the so-called thorium-based molten salt pile. I'm not saying that the current "killer whales and small nuclear fish" are going to use thorium-based molten salt piles, I'm just taking it as an example. Because the thorium-based molten salt reactor is a high-pressure system unlike the pressurized water reactor, it has become an atmospheric system, so the volumetric weight is greatly reduced. The working fluid of the reactor has changed from high-pressure water vapor to molten salt, and the problem of nuclear radioactivity has become controllable, more specifically, safe and controllable. Thirdly, the power it can output is quite abundant and sufficient for a submarine. So from this point of view, if your thorium-based molten salt is piled up and matured, then things like "little killer whales, small nuclear fish" may be popular.
Speculation without a technical basis is pure speculation. Only with a technological foundation will it be possible to have a new generation of new weapons and equipment, and it is even possible to completely replace the equipment of the older generation. Finally, I say that thorium-based molten salt piles are just an example, don't think about it.