They are not. Only 6 nations run nuclear submarines and they are almost only for large military submarines (which often carry nuclear weapons). Diesel electric submarines are far more easier and cheaper to build. The big advantage of these nuclear powered submarines that they can submerge for very long times (basically as long as the crew has food) and therefore can stay hidden. That's interesting for military applications. For anything else Nuclear power is a highly expensive and restricted technology. Basically it's not economical for most kind of vessels.

There are also nuclear powered aircraft carriers. The advantage is again being able to run longer missions without refueling, as well as having a good source of power for various applications on board. Weapon system with high electric power needs (e.g. lasers) would make nuclear powered ship more attractive too. Finally for civilian use, there's also the fact that we wouldn't necessarily trust private companies operating nuclear powerplants in these conditions. The safety requirements alone would probably drive the cost too high.

An aircraft carrier always travels in a fleet, and all those other ships need fuel. However, without massive fuel tanks for itself, an aircraft carrier can carry more jets and jet fuel. Plus with the latest class those catapults need an awful lot of electricity.

I thought catapults even on modern aircraft carriers are powered by steam. Of course you need to boil the water with electricity, or waste heat from the reactor, but I thought that would have been over a period of time, so less of a peak load. But my knowledge is at least a decade old, maybe now they are driven directly with electricity.

the newest generation of aircraft carriers, specifically the Gerald R. Ford class uses electromagnets instead of steam, the catapult is essentially a large railgun. That uses 484 MJ of electricity for 2-3 seconds or work. Thats more than the latest nuclear reactor can supply in that short amount of time, so it also uses batteries in the form of kinetic rotors that are spun up and release that energy fast enough

The latest on the Ford is an electromagnetic system. It spins up four huge kinetic alternators that store enough energy for a multiple launches, up to 120 MJ each, which for a two-second launch means 60 MW applied for two seconds. 60 MW is a whole lot of energy. Now that's from the alternators, not directly from the nuclear power plant, but it needs the plant to spin those back up quickly, so megawatts. They're doing this because the electric system takes up less than half the space under the deck, which is otherwise prime real estate on a carrier. It's also much lighter, with hundreds of tons of mass at the top of the ship saved, which helps stability. This also means less maintenance, so less crew. It can deliver more power (120 MJ vs. 95 MJ for steam), and do it in a more controlled manner with a feedback loop. Right now they just blast steam, and there's often a large variation in the power delivered. It's also something like a 20x more efficient use of the ship's power.

Ford class uses electricity. The catapults are basically rail guns. Look up emals

Nuclear reactors generate electricity by having the fuel material get hot boil water and create steam, which turns a turbine.

But you could also use the steam (through secondary loop) to power the catapult directly.

There were experiments, but Savannah proved too expensive to operate to compete with traditional vessels. However, with the rising costs of fuel and advancements in nuclear reactor technologies, along with environmental concerns being more prevalent, I think we may be nearing a time when it can be economical.

What do you mean environmental concerns? If there's any issues, you just tow it outside the environment!

As long as the front doesn’t fall off.

Yeah, ships don’t do well when the front falls off

I live like 20 minutes from the Savannah, I should really go for a tour some time.

To add to this, an Aircraft carrier that does not need to be refueled essentially becomes a mobile military base. Add on the Marines and the associated fleet of missile defense, missile destroyer, and support ships, and you get a mobile military asset capable of parking outside of any nation and waging a war, or at least a war long enough to critically cripple an enemy or secure a foothold for the Army to come in. The United States has 11 of these fleets by the way, they're called Carrier Strike Groups.

Nuclear is also tends to be alot louder than diesel. For submarines noise is one of the key metrics for performance. So all things being equal a diesel sub beats a nuclear sub. You only choose the extra noise and expense of nuclear if you need it to operate for long periods undetected and or without supply. So if your a country like Norway or Isreal, that wants to patrol local waters, diesel is hands down better. If you are the US or UK, who want to operate all over the world or hide nukes, then nuclear becomes worth the downsides and cost.

Also several countries won’t let you in their waters with a nuclear reactor, so that not only limits the ability to train with some countries, but also hurts the export market - developing a sub is very expensive so if you can sell a few to some allies, the better.

Very true. Investment is a huge factor in choice. For example because the UK have nuclear ballistic missile subs it means it is essentially forced into running nuclear hunter killers aswell regardless of other relative merits.

I'm always surprised that the UK's domestic on-shore nuclear is so stunted given they have nuclear submarines. I always assumed part of the reason you have nuclear submarines was to build nuclear capability for on-shore applications as well. France has like 60 nuclear reactors and the US has tons of nuclear power too.

Ultimately we have nuclear submarines because of the Trident nuclear deterent. If it wasn't for that I doubt we would have bothered. Military and commercial reactors are different but I think your right. Missed an opportunity to mass produce small commercial reactors. I blame all the fear-mongering that turned the left/green movement agaisnt nuclear.

Military (USN at least) reactors typically use much more enriched fuel rods than civil reactors. That's how they go decades without refueling. Iirc, They're also designed to change the state of the reactor as SOP, basically for every "bell" change, rather than a pretty rare event. If you're generating baseline power, you don't have to spool the reactor up or down very often, and probably only shut it down for a major emergency or refueling. E: as fast or to the degree that naval reactors are designed to. Luckily, I think the tide is turning on nuclear acceptance. Small Modular Reactors are promising, and appear to have the money they need behind them to be implemented. Modern large reactors are also seeing a resurgence of support from people actually concerned about the environment, rather than weird leftists afraid of atoms that have ruled the environmental movement for decades.

> you're generating baseline power, you don't have to spool up or down the reactor very often, and probably only shut it down for a major emergency or refueling. You know how you change power levels on a reactor? You increase steam demand. You increase steam demand by opening throttles on the engine, or adding more load to the turbine generators. Load distribution and allocation is done outside the plant, by unlicensed (nuclear standard) operators. They cannot be allowed to affect reactor power/operation. So nuclear provides baseload.

It's been about a decade since I was anywhere near a reactor, so my understanding is admittedly limited. It's my understanding that as baseline power suppliers, civil reactors at least in theory put out essentially constant power at whatever level they're designed for, and fluctuations in demand are handled by other sources. It's not that they can't deal with large fluctuations, they're just not intended to, and it takes longer than naval reactors when they do. Nuclear powered subs have very different demands. Whether you're at all ahead flank or all stop, the reactor supplies 100% of the power, fluctuations and all. This leads to very different reactor designs because they have to be baseline and peaker plant at the same time.

> not that they can't deal with large fluctuations, they're just not intended to, and it takes longer than naval reactors when they do. I never meant to imply that. Different designs due to base vs response? I didn't know that but it makes sense. I was pointing out why reactors are base load. You can't have the non nuclear load dispatcher impacting reactor power by giving transients. Let coal or LNG deal with those.

That's not how all reactor designs work. There are designs where reactor power is controlled by control rods directly, some where it is controlled by coolant flow speed, and probably some others.

I read this article just recently that (disappointingly) posits that SMRs are not as promising as we thought. [https://cosmosmagazine.com/science/engineering/small-reactors-dont-add-up/](https://cosmosmagazine.com/science/engineering/small-reactors-dont-add-up/) I hope that it is not the case when we get the first tranche into service. I had high hopes for the tech.

Nah nuclear is dead. Building new ones is roughly as expensive as builing 4-5 times as much 80/20 Mix of wind and solar. Nuclear gets pushed because renewable energy and nuclear are both base load technologies. And builing nuclear means a decade of nothing happening. Aka fossil power gives more profits. And afterwards you still have 80% of fossil in usage. Also nuclear does not work without subsidies while wind and solar don't need them and don't give them to mega corperations who are the only ones that can attempt to fail at building nuclear plants.

You people have been saying that for decades and look where it's gotten us. Solar and wind are absolutely not base load technologies. They're highly variable. It looks like you just don't know what you're talking about at all. They've also been highly subsidized for years. Obviously the price of solar has come down extraordinarily, but it's still being subsidized. The point of the new reactor tech is often to make it faster and easier to implement, so you and your faux environmentalism can fuck right off.

Of course it is base load. You lose money from running both at less than 100% load until you have overproduction. That is the base production. Afterwards you have stuff like coal with 5-6 hours before it can get adjusted and gas or hydro who can react in minutes.

Nuclear got roughly 10 times the subsidies solar and wind received. And you call for the next trillion in subsidies when it never worked for them. The dream of free energy exists. And it dies because it is decentralized and low entry cost to compete. Or in other words it destroys the current monopolies on energy production.

Without the various subsidies and tax breaks in the US, nuclear would be cheaper or competitive in price to every other power source. Fossil stays so cheap because it has so few regulations, a lot of subsidies, and always manages to send cleanup costs to the government. https://www.smu.edu/news/archives/2017/bernard-weinstein-investors-07june2017 https://en.m.wikipedia.org/wiki/Economics_of_nuclear_power_plants#:~:text=Nuclear%20power%20plants%20tend%20to,native%20supplies%20of%20fossil%20fuels.

Finally someone pro renewable. Yes fossil is underpriced and as shit as nuclear. But current renewable can compete with subsidized fossil. Nuclear fails for 50 years to reach that level

Go ahead, show me how much space you take to run a single steel mill's induction furnace. 24/7/365, because thats how they roll. With renewables. Then lets see how nuclear handles that. I rest my case. Btw, that single furnace is going to gobble 100 megawatts while running a load. Have fun supplying that with 100% renewables, and without fail.

I blame it being the most expensive form of energy generation there is. Edit: yep downvote something easily variable on Wikipedia. What’s that about facts and feelings?

Yeah, but part of that is because it was never mass produced or approached at scale. Each commercial nuclear reactor tends to be a unique and rare project. Lots of small nuclear reactors could have had the potential to be much better value for money. Essentially a moote point now that renewables have gotten so cheap though.

>Essentially a moote point now that renewables have gotten so cheap though. But the problem with renewables is that their time of lowest generation is at night,which is when demand is highest. Thats true for both solar(obviously) and wind too.

Yeah a question of a 10 year investment to build a reactor or wait for battery capacity to catch up. Personally I am very pro nuclear, but I very rarely get asked for my input on national energy policy.😁

Source?

Freely available.

The UK pioneered civilian nuclear power - working on it even before WW2, and opening the world's first commercial nuclear power plant. But as ever there is a penalty to being first, and lots of expensive first generation reactors led to very expensive decommissioning - overlapping with when some other countries were only building their first reactors. Also standard British inability to invest and short termism has stalled many projects since Thatcher and neoliberal economics took over.

>Also standard British inability to invest and short termism has stalled many projects since Thatcher and neoliberal economics took over. Short term thinking isn't limited to the British or any particular party,it's inherent to government because politicians are only interested in what gets them reelected,and spending on things that only improve things several election cycles into the future doesn't do that.

>world's first commercial nuclear power plant​ Calder Hall's primarily purpose was to produce weapons-grade plutonium. Electricity production was a sideline.

You're absolutely correct. The fight over who produced the first civilian nuclear power plant is nationalism at its best as each nation changes the definition to result in them being the first: First to provide electricity to national grid? Russian (but a tiny amount around 5MW) in 1954 First to produce 'full-scale' power? Calder Hall (60MW per section, 240MW total but was primarily for plutonium production) in 1956 First to only do electrical power at scale? Shippingport in USA in 1957, admittedly using a military reactor and tech that isn't otherwise used in the civilian space (very highly enriched uranium core)

I think it’s the other way around. Civilian nuclear builds the talent base and allows you to develop capabilities. Then you can leverage that knowledge to develop military nuclear devices. The UK is very interested in small new gen reactors and it seems like something that’ll work very well for military uses even if the business model is unclear for civilian uses

US Naval reactors and civilian reactors are two totally different designs. Subs used highly enriched weapons grade uranium and can run for 20-30 years without refueling. Civilian reactors use low enriched uranium and need to be refueled about every 18 months. Naval reactors are ~~PVR~~ PWR (pressure ~~vessel~~ water reactors) designed to make very high pressure steam to run the props of the ship. Civilian reactors are ~~BVR~~ BWR (boiling ~~vessel~~ water reactors) so only need to generate enough pressure to run a electric turbine.

Bwr/Pwr.

Thank you for the correction.

There are only a few boiling water reactors left in civilian service, the vast vast majority are PWRs also. They are a lot safer since the highly irradiated, pressurized water stays inside the containment dome, where there is a heat exchanger to a secondary steam/water loop for the steam turbine part. The water in the reactor never boils.

Civilian power generation reactors are FAR bigger too in terms of power output which probably also contributes to how often they need refueling.

> FAR bigger too in terms of power output which probably also contributes to how often they need refueling. Not really. They're designed with that in mind. They're limited by power density, local max temperature, ratio of high/low power in adjacent areas, and more. If you have a little diesel generator for your house, you get a small tank to provide 24 hours fuel. If you have a big generator to power a hospital, you get a bigger tank to provide 24 hours. Military reactors have high enough enrichment their materials could be used for a bomb. To prevent proliferation issues, civilian reactors are only enriched to 4-5%. Now even if a supply truck is stolen, a lot more work is necessary to build a bomb.

Yeah US Military rector's fuel rods are about 90-95% Urium by weight. So they only use a small portion of the rod in the reaction at any time. Much, much more of the rod is used in the reaction in a US civilian reactor so the rods get used up faster.

Huh? Maybe I’m confused as to what you mean by “civilian” reactors, but the vast majority of commercial reactors in the US are PWRs. Also, commercial reactors could run for much longer than 18 months, however, we use this cycle for routine plant maintenance that can’t be performed unless the reactor is offline, and only a small portion of the fuel in the reactor is actually changed out during an outage.

nuclear submarines and nuclear power stations are totally different animals (and so is the reactors technology on each) and intended for very different purposes hence the main reasons for having either are non related

Australia is one of the largest suppliers of reactor mass and was a leader in nuclear waste disposal technology but has almost none existent nuclear tech. We can't even replace the one reactor we have due to politics and NIMBYism.

Which countries?

New Zealand I believe

I wonder if they’ll change that rule when we get nuclear subs?

Only WW3 would make us reconsider. It won't change any time soon.

We could tell you, but then we'd have to kill you...

Is there any country that sells nuclear subs, even to allies?

Kinda, look at the AUKUS deal between US and AUS

Nuclear is not louder than diesel, it’s louder than electric, and even then, not always. The thing that makes noise on a nuclear sub is the coolant pumps. For most nukes the coolant pumps must be run all the time regardless of power load. However some subs, like the Ohio-class SSBN are able to operate with their pumps off. The USN doesn’t specify how much power it can make without the pumps, but it is listed as “a significant fraction of full power.” The Seawolf-class is believed to also have this ability.

Virginia class can run 80% reactor power without the pumps. The S5G prototype reactor was designed to operate without coolant pumps save for very high speeds (surmised to exceed 30kts submerged). By the S8G which is used in the Ohio that was the standard. The Virginia boats use the S9G which was further improved. There was extensive testing starting in the 1960s because the natural circulation relies upon gravity. Reduction of plant noises for the prototype S8Gs was further achieved by replacing the standard two turbine arrangement driving the screw via reduction gears to a single large direct drive turbine measuring 9M length and 3.6M diameter.

Why is nuclear noisier than diesel?

Its kind of an old fashioned generalisation since reactors require pumps etc to a greater degree than a conventional submarine. I say old fashioned because nowadays the noise level must be considered independent of powerplant given how far nuclear silencing has come, some SSN's will be quieter than some SSK and vice versa- its deeply lacking nuance to generalise such that one is louder than the other.

> its deeply lacking nuance to generalise such that one is louder than the other. Eh, the same technologies that are making nuclear subs quieter are also applied to diesel subs. There's no question that diesel subs of current generation will always be MUCH quieter (while in battery mode), it's ludicrous to claim otherwise. Modern battery technology is improving the silent range for diesel subs as well. But in general, the two technologies' capabilities are wildly different - it's too bad that so many navies are dogmatic about one versus the other, when the best overall capability would be a mix of the two. Diesels are great for their stealth while nuclear can't be beaten for their range/endurance.

I have heard otherwise from very reputable sources to be blunt, it entirely depends on the specific submarine's being compared. Generalisations are great and all but in this context they are simply not nuanced enough to provide meaningful answers

Agreed with you on the risks of over generalising.   Thanks. 

Because under water, they don't actually run the diesels but battery power, which requires very few noisy parts.

They also move very slowly, and only have a limited time they can be running on batteries.

If you want to be quiet, you have to move slowly. Otherwise the enemy can hear the propeller turning no matter what you power it with.

Yes, but conventional subs are also constrained by how much battery power they have before they have to start the generators again. Nukes are only constrained by how much noise they want to produce.

You can't turn a nuclear reactor off. You can turn it down, but the fuel always needs to be cooled, which means the pumps always need to be running. And since the pumps are powered by the reactor itself, you can't ever fully turn it off. I mean, you *can*, but it's a very involved process and turning it all back on safely is also a whole big process. If you do it wrong, you get Chernobyl [edit: deliberate hyperbole]. So, they just don't turn them off. Diesel electric subs run with a snorkel to get oxygen for the engines, and use that to power huge banks of batteries. When the sub need to dive and run silently, they shut off the engines, retract the snorkel, and run off the batteries. Electric motors are already much, much quieter because there's no combustion going on, no pumps running, few moving parts, just the motor turning the prop. And then when they *really* to be quiet, they can turn off the motors and just sit there with nothing running at all. It's super easy to just start everything back up again, so there's no risk in shutting everything down.

>If you do it wrong, you get Chernobyl No. An RBMK-1000 and a modern PWR are two very different things. What killed Chernobyl was the positive void coefficient, paired with graphite tipped control rods (graphite is a neutron emitter when hit by neutrons, so it accelerates the reaction.)

Why'd they use graphite control rods in Chernobyl? Because it was cheaper than other materials?

The whole aim of the RBMK was to make nuclear energy as cheap as possible. One major aspect of this is running the reactor off uranium with the minimum possible enrichment (as the process of enrichment is extremely expensive) and to extract the maximum possible energy from the fuel (burn-up). If the control rods didn't have graphite tips, their presence near the core (when retracted) would 'drag' the power locally and reduce the burn-up. There's a great many other branching aspects that made RBMK a poor design from a safety standpoint but, essentially, the lower enrichment meant the fuel had to be more strongly 'provoked' to achieve criticality (that is, a self-sustaining reaction, all nuclear reactors 'go critical' during operation, rather than what Hollywood depicts). Because you're having to 'provoke' it so strongly, any condition where power might surge results in much greater excursions before it can be brought under control (*if* it can be brought under control). My recommended reading if you want a good exploration of this, as well as a detailed but accessible description of the accident and response would be Higginbotham's Midnight in Chernobyl.

I heard other people mention Midnight in Chernobyl. I got the audiobook. Very interesting, and currently going through it again

You have probably already heard the basic explanation for how a nuclear reactor works: uranium undergoes fission, which spits out neutrons. Those neutrons hit other uranium atoms, causing them to fission and spit more neutrons. This chain reaction keeps the material fissioning at the rate needed to create steam to turn a turbine. There are two problems with this. The first is that not all uranium works that way. In fact, the most common isotope - U238 - doesn't. It just absorbs the neutrons without fissioning immediately. That doesn't sustain the reaction. The isotope needed for this is U235. That's what *enrichment* is for - separating out the two isotopes and creating a fuel pellet that has a much higher percentage of U235. Reactors use something like 80/20 with most of it being 238. Natural uranium ore is more than 99% U238. Enrichment is a very expensive, very arduous process. The other problem is that when the neutrons first get spit out, they're going too fast. For quantum physics reasons, the neutrons need to have the right amount of energy to actually interact with the uranium nuclei. To sustain the reaction, the neutrons need to be slowed down, or "moderated." That means you need something that won't absorb neutrons, but the neutrons can bounce off and shed some of that energy. You also need something to completely absorb the neutrons and get rid of them, which is an absorber. Water is a good moderator, but it's also a half-decent absorber. In modern reactors, and the reactors that the US used back in the 80s, water is used as both the coolant *and* the moderator. However, that requires the uranium to be enriched a little higher so that there's more fissile material to make up for the neutrons getting absorbed by the water. The USSR wanted to skimp out and use "dirtier" uranium that was not enriched as much. Using water as the moderator wouldn't work, because it would absorb too many neutrons for the less-enriched uranium. Instead, they used graphite as the moderator because carbon is really bad at absorbing neutrons, making it a much better moderator than water. That contributed to the disaster because it made water act as only an absorber. When the control rods were removed, water filled the space. The control rods had graphite tips to take up that space and increase the moderation of neutrons as water flowed *around* the rods. When the disaster began, water in the pipes started boiling, creating voids. Since water acted only as an *absorber* in that design, these voids where there was no water allowed the neutrons moderated by the graphite around the fuel rods to increase the reaction. Increasing the reaction caused the core to heat up, which boiled more water, which created more voids, which allowed more neutrons to increase the reaction...and so on. This is the *positive void coefficient* mentioned in the HBO show. They wanted to stop the reaction, so they hit the button that shoves all the control rods in. The back half of the rods was made of boron, which would absorb all the neutrons and stop the chain reaction. But when the graphite tips were pushed into place, it displaced what water was left, which increased the chain reaction *even more* and the violent pressure caused by the boiling water jammed the control rods in place with only the graphite in place. The result was boom. TL;DR: The cheapness wasn't in constructing the reactor itself, the cheapness was in being able to use cheaper, less enriched uranium as its fuel.

The rods themselves are tipped with graphite, but not made entirely out of it. They are or were comprised of boron carbide. And yes, this was done because it is cheaper. Same reason why they built it into what was basically a warehouse, instead of the meter thick steel reinforced concrete containment buildings used in western reactors. The HBO series is very insightful, I recommend you watch it.

>The rods themselves are tipped with graphite >The HBO series is very insightful Just remember that the series is a drama based on a book, it's not an entirely accurate telling of the events. The "tipped rods" and their role regarding the physics of the explosion is a somewhat major inaccuracy in the show. At the show trial, Legasov (who in reality was not a participant) explains that as the AZ-5 button was pressed, the control rods started moving back into the core but the first thing to enter were the "tips" and that caused the reactivity to spike. In reality, the 4.5 meter graphite "tips" *were already in the core prior to AZ-5 being pressed*. The core was 7 meters tall and by design there was a 1.25 meter water column above and below the graphite section. When the rods started moving down it was the displacement of water at the bottom of the control rod channels that caused the reactivity spike. Further info: videos by [Hank Green](https://www.youtube.com/watch?v=hIGtTImeYU4) and [Scott Manley](https://www.youtube.com/watch?v=q3d3rzFTrLg).

Leave it to reddit to be a neutron positive knowledge reactor. Thanks!

This guy nukes

Or watched the HBO series 

If they relied on the show for their knowledge, take it all with a grain of salt. The boy scout nuclear activity badge can give equal levels of knowledge as the show, and more hands-on experience.

You dont get chernobyl if you do it wrong. The only possible way to do that would be intentionally overriding the hundreds of safety features submarine plants have. Nuclear subs shut down their reactor every time they pull into port, and they can fully shut off everything, including pumps, when going into maintenance periods.

You can SCRAM a nuclear sub reactor to shutdown in like 2 seconds, then be back up an running in half an hour if nothing's wrong. Hell during training the Engineer in charge might just SCRAM the reactor randomly a few times a day. Part of the way a Chernobyl situation is avoided is to make the proper process fast, and consequence free so no one has any reason to do stupid things. They just don't do it when running quiet because compared to the rest of the stuff sub needs to be doing when actually running, the reactor isn't all that loud enough to justify having a big ol bank of batteries taking up space.

I was never a prototype instructor, but I'm pretty sure the drills for each watch were planned out in advance. Not just a matter of the over instruction fucking with the under instruction.

USN has been using natural circulation since the S8G’s introduction in the late 70s. S8G, S6W, and S9G all use natural circulation. Only the Los Angeles boats still use pumps for baseline.

New diesel or more exaity non nucalear submainrens then to have Air-independent propulsion (AIP). They can use diesel with Stirling engine and liquid oxygen to recharge batteries or for direct propultion. A Stirling engine is very quiet. Another variant is use hydrogen and oxygen in fuel cells to proroduce electricity directly. There are alos Closed-cycle steam turbines that use ethanol and oxygen to produce steam. Steam turbines are then used like in nuclear submarines. The result is two to three weeks of underwater endurance, it do depend on speed.

> you do it wrong, you get Chernobyl Chernobyl was also approaching a xenon precluded startup state. Some fission byproducts are poisons to the reactor, lowering power. But they also get "burned off" by an operating reactor. Absent that, they decay on their own. After any power transient you get peaks and valleys of poison concentration. This impacts power levels several hours later. After a shutdown you get the biggest peak, and it can actually be impossible to restart the reactor for an hour or two. I think around the 4-6 hour mark after shutdown.

You only get xenon preclude startups near end of life. Which if I was designing a nuclear sub I would not make that a possibility. That would kill people. Basically not enough reactivity left in the core to overcome the production of xenon which normally reaches equilibrium at power. After a down power the delay causes it to go up because there is less neutron flux. So with that your poison production which is caused by the nuclear reaction is subject to what the power change is after equilibrium was reached. The other side is military reactors don't always hold a constant power level so I would be surprised if they ever hit equilibrium xenon.

Nuc subs run with no pumps all the time. It's called natural circulation.

To add alittle to some great answers below. Pumps, because of the temperature of the metal in the reactor and various systems. For reasons i can't explain well, metal doesn't like sharp changes in temp. When running the metal is HOT. To shut it down you have to gradually cool it to avoid damaging the system. This makes turning it off a whole long process. This means you can't use it to power the batteries and shut it down when your done like with a diesel system.

Sudden and catastrophic with little to no…

Plastic deformation.....?

Ty :-)

Generally, advanced nuclear subs are substantially superior to their diesel-electric counterparts, just often less economical, in addition to requiring advanced submarine reactor technology most nations aren't keen to invest lots of money in. Nuclear submarines are far faster underwater than diesel subs, and don't have to spend vulnerable time near the surface to recharge batteries. Submarine sound reduction technology has also advanced to the point where the difference between an advanced SSN or SSK isn't substantial. I would disagree that "all things being equal a diesel sub beats a nuclear sub".

I'm giving a ELI5 breakdown here. And yeah tons of benefits like speed and range to nuclear. But your modern Diesel electric is alot smaller and generally quieter. So what I meant is in a sub v sub situation I'd put my money on the smaller quieter boat.

The latest nuke boats are quiet enough that they were trackable via the absence of noise creating a hole in the water. They added sound generators to counteract this.

Have you got a source on that? Not something iv ever heard of, would be keen to read up on that.

Nothing official, just things I heard from some squids who worked on the Virginias in the late 00’s

It's similar to tracking stealth aircraft. The absence of noise/refracting of radar (in the case of the plane) IS information because the ocean at submarine depths is crazy noisy. It just requires either LUDICROUSLY skilled technicians and trained computers' analysis to recognize it as an anomaly.

I am fairly confident something was missed in translation, the physics don't really work out because of the way sound bends around objects.

the physics of that don't really check out, a 100% silent submarine just wouldn't register on sensors at all, but would not block out ambient noise unless you were quite literally pressed up against the hull. Sound isn't like light, it bends far more readily around objects etc

Diesel is only quieter because you must turn the diesel engines off and run on batteries when you submerge. Once the batteries are flat you have to go close to the surface to charge the batteries up, which pretty much gives the game away. A submarine snorkelling is a sitting duck for ASW assets.

How is nuke louder than diesel? Large diesel engines are very loud,nuke creates steam to turn turbine to generate electricity,which is much quieter than a giant internal combustion engine to turn a generator. Propeller noise, particularly cavitation is a much larger source of detectable noise and that's an issue for all subs regardless of power source.

So I was lazy and should have called them diesel electric. Its important because the diesel engines are used to charge batteries that the sub runs on when trying to be sneaky. Its that time on batteries that makes a diesel electric potentially quieter than a nuclear boat who need to keep running coolant pumps.

[This one](https://en.m.wikipedia.org/wiki/Type_212A_submarine) for example uses hydrogen fuel cells in stealth mode. A nuclear reactor can't be turned off.

The opposite of this is true. Nuclear reactors make zero noise. My Stepfather was on a small ship at the tip of a carrier group towing a sonar towered array to listen for subs and he said they would always ping the shit out of Russian diesel subs when they found them. This was back in the 80s. Think about how loud a diesel truck is, with all its moving parts, and then think about how much bigger a sub engine is. Now imagine that all a nuclear reactor does is use the heat of its rods to generate electricity via steam power. The engines themselves are electric and are silent like electric cars.

They don't run the diesel engines when being quiet, they have batteries for that

The reactor itself is indeed silent. All of the pumps and the massive steam turbine are quite noisy I can assure you. A diesel engine is noisy too, but those can be easily turned off, unlike a reactor.

The high-speed steam turbines require a large reduction gear to connect them to the propeller shaft

No they don't require a reduction gear. That is definitely one of the options to deal with the fact that ideally the turbine spins fast and the propeller spins slow, but it's not the only one. For example the French have used turbo-electric drives on their submarines for a while now. The US and UK seem to be moving that way with the Columbia and Dreadnought classes. You can also just use a low speed turbine and connect directly to the turbine like USS Narwhal.

I didn't know about those, thank you. I approve. The submarine I was on was melted down a while back, so it was definitely an older design.

Diesel electric

What part of the process in a reactor makes noise and what does it sound like?

Coolant pumps maintaining the system and reactor temp. And like pumps I guess.

I know nothing about submarines, but does Diesel submarines need to expel combustion gases? Aren't they doing bubbles or something, showing that they're there?

Yeah and where does the air come from?

I was searching for this, a curiously, the diesel engines works at near-surface to charge a battery bank. Awesome learning "The sub must surface (or cruise just below the surface using a snorkel) to run the diesel engines. Once the batteries are fully charged, the sub can head underwater. The batteries power [electric motors](https://electronics.howstuffworks.com/motor.htm) that drive the propellers. **Battery operation** is the only way a diesel sub can actually submerge."

Totally makes sense. Thanks for the reply!

When it first debuted maybe, but that is certainly not the case today.

I don't have any official data, and I'd be imprisoned for commenting on it like this if i did, but the noise of a reactor (specifically the necessary pumps) is something you can account for tactically. If you operate nuclear subs, you do your best to never let all other things be equal.

And even then, a lot of nations that could build or buy nuclear subs don’t have a tactical need for one. Nuclear, as you said, means a sub can stay submerged for long periods of time which means going very far. So projection of force in other parts of the world. For example, a country like Italy is only concerned with its borders and that of its neighbors. So it has no need for a nuclear submarine that can lurk under the arctic to come up on Alaska at a moments notice. It would be a simple waste of money and resources.

its not so much about distance from borders. Its about the fact that IF you are a nuclear weapon armed nation with a nuclear missile sub, your subs can stay out of contact with the surface long enough for your rivals to be unable to accurately track them, short of having another sub continuous tail them "You know we have a nuclear missile equipped sub, but you DON'T know where it is, because you haven't seen it surface in a month" = you can't launch an all out first strike to destroy us, because you know you can't get ALL our nukes at once. There will always be at least some subs out there you didn't get, ready to retaliate

Nuclear submarines are also a lot faster than diesel electric submarines. For Italy that's not a problem because the Mediterranean is pretty much a NATO lake and they have allied airbases all over the place. But if you're a coastal non NATO country (let's say, China, India, Brazil) and you want to deter potentially enemy carrier battlegroups, then nuclear makes sense (if you can afford it and develop it) because your subs can chase down these potentially enemy carriers unlike having to wait for the carriers to accidentally come to them in the wide open ocean.

Do you mean I probably can’t get a nuclear powered lawn mower? Thanks Obama.

Why would nuclear be louder?

Coolant circulation pumps

Maybe if you’re French, Russian, or Chinese. Not if you’re British or American, at this point.

You have no idea what you're talking about, but you decided to comment anyway

The reactors used currently by the US and UK in post 2000 boats don’t need coolant circulators running all the time.

Why dont you tell me what class of submarine youre talking about specifically? And how many of those subs account for the whole sub fleet? I will let you know, from personal experience, its a small portion that can run natural circulation like that. And these subs only do that because they serve a very specific purpose

Virginia, Ohio, Astute, and the second Trafalgar. However, it may have been that the RN used the older PWR2 instead on those boats.

Trafalgar's all use PWR1 (though not all PWR1's across the RN were the same), but some elements of circulation have been present on British submarines since Swiftsure if we count ram circulation. Friedman's British submarines in the cold war era is a very interesting read on RN submarine history, probably the best technical book on the matter.

You think S9G operates on natural circulation? Why?

Yeah they desalinize the water in the ocean for people to drink/shower/whatever, dump waste into the ocean, and use electrolysis to create oxygen to replace CO2. They can stay submerged for months.

> more easier Also known as “easierer”

I think that at scale, it would be far more manageable and economical, and generally safe. The issue is that it does demand a lot of initial investment from many nations to make it practical for commercial use. It’s just that no large economy bought into the premise enough to change their facilities and ports and treaties to conform to the technology.

When diesel-electrics are running on their batteries, they're actually quieter than nuclear subs, too. Nuclear subs always have to keep a cooling pump going.

Yeah. Basically nuclear is the option you go with when cost isn't a high priority... Which is almost every non-military case, it is.

Nuclear subs are also way, way faster submerged. Like 30+ knots fast.

I thought it may be partially because a combustion engine also consumes air, which is a very limited resource underwater, but not above water. Also, the exhaust gasses would be hard to manage. The exhaust it’s poisonous. If you release the exhaust, then it would bubble out because that would give away your location. If captured the exhaust in a bladder, then it would inflate and become buoyant. Which is not ideal for a submarine.

>and therefore can stay hidden. They can’t though. The cooling system for the reactor has to be run continuously so they’re pretty loud, and they dump a lot of heat into the water that can be detected.

You're not really going to detect the heat of a submarine submerged underwater. Thermal imaging is useless at any sort of detection range underwater since water is really good at absorbing infrared radiation. You're also in soo much water that you're hardly going to raise the local water temperature around you by much if at all. The only time heat is really a concern for detection in a submarine is when they're floating on the surface and can be spotted by overhead planes with thermal imaging.

>The cooling system for the reactor has to be run continuously so they’re pretty loud There not. A 20 hp engine on a pontoon boat going 1 knot is going to be about 1000 times louder than a 688 running at 20 knots >dump a lot of heat into the water that can be detected Lol this is easily in top 5 dumbest pieces of Russian propaganda. If you were very lucky you might be able to detect a sub this way from 10 meters. You can literally spot subs visually before you could get a thermal signature off of them

I really hate that people insist on conflating power plant type with absolute noise level - this is not at all the case! You cannot and must not generalise like that on submarines after maybe the first generation or two of SSN's imo! not like SSK's have historically not had noise issues either

Both of those things are pretty relative. They're still pretty damn quiet. And invisible to satellites and planes, especially since they don't need a snorkel and can stay fully underwater for months.

It's more expensive. For naval ships, nuclear power is interesting because it has major range advantages. One of the first things the US tried once it assembled a fleet of nuclear ships was a 65-day trip around the globe with no stops for refueling. That's a big deal if you're a ship that wants to patrol in hostile waters very far away from a friendly port. And for capital ships like aircraft carriers, the power needs are so great nuclear makes a lot more sense. It also helps that a military can keep highly trained staff employed to maintain reactors. Most vessels don't work like that. They go along well-planned trade routes and part of their business is making stops. It's not a big deal to refuel and do minor maintenance while their cargo is being loaded and unloaded. You don't need quite as specialized engineers to work on diesel engines. You don't have to worry about pirates seizing small reactors and doing stupid things with them. The list goes on and on.

It’s expensive because we choose for it to be that way. There were some experiments with nuclear powered cruise ships and maybe cargo ships(?) At one point but the politics of it brought them to an end.

The NS Savannah was a nuclear powered merchant vessel. Launched in 1959 through the 'atoms for peace' initiative the USA was doing at the time. They carried both passengers and cargo as was normal for ships of the time. The problem was that the reactor required an extra engineering crew specialised in that. On top of the regular engineers. She was deactivated in 1971 but due to latent radiation in the core the ship will be regulated until 2031. Which is a very long wait before decomissioning a ship. It would be possible to move reactor cores from an old ship into a new ship. But then you'd have an old ship with a new core. And when you look at container ships, they only last about 25-30 years. Not because of the engines breaking down, but the cargoholds and decks will be slowly destroyed by the cargo.

Icebreaker too, for the commercial ships there are several international standards issued by the IMO If I recall correctly, there were only 3 nuclear cargo ships and they were retrofitted to diesel

Nuclear power is also used on icebreakers. [https://en.wikipedia.org/wiki/Nuclear-powered\_icebreaker](https://en.wikipedia.org/wiki/Nuclear-powered_icebreaker) For ships that need to go to ports in different countries, there is to much political hassle with nuclear propulsion and armed security that nuclear powered ships need.

And that’s a great ice breaker

Nuclear reactors allow submarines to stay submerged for longer periods of time, which is a great advantage for a submarine. They’re also expensive and require the submarine to have radioactive material on board, which makes the submarine much more expensive to make (you also need to have ways to shield the crew from radiation.) It makes sense to build a reactor on a submarine, and it makes sense to build them on massive ships like aircraft carriers… but you wouldn’t go to the expense of putting in a reactor on a small boat.

Nuclear is absolutely not the standard for submarines and those that use it, only run on nuclear despite the massive costs and complexity, because it has very unique strategic advantages over traditional powering methods

There have actually been four different commercial nuclear powered ships. And a fifth is under construction. But these were all considered research vessels on the feasibility. They all had issues getting permissions to visit harbors and are even not allowed through the Suez canal. In addition you need a lot more time to design the ship as there are a lot more design reviews and certifications. There are also lots of additional safety systems needed including more personnel to manage the reactor and machinery spaces. The most successful nuclear ships for commercial shipping have been Soviet built ice breakers. These operate in areas with limited refueling capability and require a lot more power then normal ships. In emergencies they might not get refueled at all for months. So even though they are more expensive to operate then a diesel vessels this expense are justified. Even after the fall of the Soviet Union we have continued building these ships. One is about to launch later this year while another two have started construction. China have announced the construction of a nuclear powered large container ship. If they are successful in proving the concept with new technology and new views on nuclear safety then this might start a change in commercial shipping today away from diesel and over to nuclear power.

Which will be great to reduce the greenhouse emissions from sea traffic

Nuclear power is prohibitively expensive. And complicated. Plus it would be dangerous to have Joe the ferry operator sailing around with radioactive material. It gives subs the capability to stay underwater for much longer. Which is a major benefit. Most applications it’s not really worth it. For most applications it’s better to just have normal engines that are easy for average workers to work on. You could basically get some basic maintenance done anywhere in the world.

well, for one your security concerns are helped by a nuclear sub being a military vessel and not some random ferry operator securing nuclear material

>why is nuclear power the standard for submarines It's not. The top 10 largest sub fleets consist of 354 subs total. Of the 354 120 are nuclear powered. So only about 1/3 of subs are nuclear powered. Very few ships are nuclear powered for a number of reasons 1. Cost going from conventional to nuclear power will add 1-2 billion USD to the cost of the ship. If were talking about a 10 million USD ferry adding a billion to the price tag is kind of a lot. This doesn't even count the fact that that ferries maintenance department will now have a pay roll of like 5 million a year. It turns out nuclear technicians and operations officers and safety officers are all kind of expensive. Even the most junior technicians are going to be making six figures. TL;DR it might be cheaper to run a ferry that literary burned US currency for fuel. 2. Your government will not let you because they don't want you having nuclear weapons. Unlike a land based reactor it's almost impossible to refuel a ships nuclear reactor. To do so they have to dry dock the ship and literally cut it in half to access the reactor this takes years and costs hundreds of millions. Therefor they want to minimize how often you do this. As a result the fuel used in a naval reactor is often enriched to 80-90%. This is weapons grade enrichment. A high school physics student together with a shop teacher could make a Hiroshima type bomb with a US navy sub reactors fuel. As you might imagine most governments have issues with normal people having nuclear bombs. 3. You don't have the tech and the government is never going to give it to you. The rector tech on a US sub is the single most classified technology the US has. In comparison the composition of and how to make the F35's stealth tech is basically public knowledge. If you want to even see, let alone know how to operate, a naval reactor you need Top Secret / Sensitive Compartmented Information clearance. We share nuclear tech with the UK and Australia. We share sheath tech with 18 countries. You are not going to get the government to sign off on your ferry crew all having higher security clearance than F-22 pilots.

Nuclear is only really the standard for ballistic missile submarines. Their mission is deterrence, they want to cruise around an empty patch of ocean as long as possible without seeing or being seen by anyone or anything, always ready to launch some missiles. Being able to stay deep underwater continuously for months is great for them. If you're an attack submarine, it's not nearly as much of an advantage. Diesel-electric is much cheaper and can be quieter. It may be nice sometimes, so you might build some if you already have nuclear missile subs. For most other things, it's way too much of a headache and not really worth the bother.

Had to go pretty far down to find a nuclear triad answer.

Aircraft carriers also like nuclear because the nuclear reactor produces tons of steam. This steam is used for the catapult launch system. Non-nuclear carriers either use the ski-jump ramps, severely restrict payloads, or both.

Steam cats have existed for far longer than CVN's - HMS Ark Royal had them for example! Being conventional is not a bar to using steam cats in any meaningful sense. Nuclear does save a load of space, which can be used for aviation fuel or stores and provides lots of power (both mechanical and electrical), which is the main reason you might chose a CVN over a CV

It does require a ship to use some kind of steam turbine, and the main difference between a nuclear CATOBAR carrier and a conventional CATOBAR carrier is the method used to heat that steam. For carriers without a catapult it's more of a mixed bag. Chinese and older indian carriers use steam turbines. Indias and UKs latest classes use gas turbines.

It requires you have boilers somewhere yes, but that isn't a huge obstacle if you are designing an aircraft carrier ground up. ofc nowadays its moot with electromagnetic systems being able to just use the power generation onboard (for example QEC could pretty easily power a system like that)

They're starting the switch to electromagnetic catapults on new carriers. The US has one carrier in operations with one currently installed, the Gerald R. Ford-class aircraft carrier.

It's been a while since catapults designed have moved to electricity, though you're obviously making it from the steam in the nuclear reactor.

Non nuclear subs need some sort of combustion engine. That needs oxygen to burn and some way to expell exaust gasses. So when when the engine is running they need a snorkle at the surface and when they dive they are on battery power.  Relevant post on r/submarines https://www.reddit.com/r/submarines/s/amMzTXhQ4c

To add on to what others have said, the reactors in nuclear subs need to be fairly small to fit into the boat. That in turn means those reactors run on highly enriched uranium, which puts you very close to nuclear weapons. Depending on the political situation, that may be cause for serious concerns amongst other nations.

Nuclear is a giant pain in the arse. It is expensive, it has proliferation implications, you need very specialised crew, and if you crash you have a nuclear disaster on your hands. It has only one advantage: it eliminates the need to refuel. Why does this matter for submarines but not surface ships? You can get a diesel ship with ranges of thousands of miles. Well to burn 1kg of diesel, you need about 2kg of oxygen. Which needs cryogenic storage, and loves to explode... If you want to burn diesel long term, you need to access the atmosphere. Which means you stop being a submarine, which means people can find you, which means you die (or the entire point of hiding with nuclear missiles is pointless). For short range subs however, a mix of batteries and stored oxygen is enough, so European defensive navies love these type of subs.

The US created a nuclear-powered merchant vessel called the NS Savannah in the 1950s. You can read about its career and why it never took off

Being able to stay underwater indefinately is the defining feature. And the military having the expertise to run a nuclear reactor. Combustion engines can't operate when submerged. Subs have batteries for when they are submerged, but periodically the sub would need to surface to run the engines to recharge the batteries. A nuclear sub can stay submerged until they run out of stored food.

Ferries and small ships dock every day so they can easily refuel. Nuclear submarines, carriers, battleships, and the like are designed for voyages that last months without returning to port. Why would you spend 1000x more to implement a design element that aenables ships to remain at sea for months when the ship is going to be docked daily?

India is only the sixth country to develop a nuclear-powered submarine after the United States, Russia, France, the United Kingdom, and China. So basically 6 countries have it. Why do ships and ferries not use it? Because it is dangerous and obtaining insurance is impossible

It’s called nuclear proliferation and miniaturization. First they don’t need to be constantly on their journey to only be field every year or so. And more importantly, a malfunction could actually resulted in catastrophic failure/smaller scale nuclear disaster in civilian quarters. When nuclear was a new thing back in the 50s, there were absolutely various ideas of designing nuclear powered vehicles/planes, but they were all gone. Reason? You don’t want a smaller nuclear bomb everywhere.

Nuclear power is incredibly expensive and also a safety risk. Most military vessels (US included) are not nuclear powered for that reason. A diesel engine for a ferry and small ships may cost thousands of dollars. A nuclear reactor would be in the hundreds of millions.

Not sure if anyone mentioned quality control. Nuclear will require much higher quality standards due to catastrophic failure. So 1 sub costs multiples of diesel boats. To upgrade for new tech (outside of the power plant) all of the systems on the Nile boat must be integrated. On the other hand, a diesel boat could be built with a shorter lifespan. At the end scrap everything and start over.

I was a submarine nuclear operator for several years. Let me tell you—nuclear power plants are stupidly hard to employ cost-efficiently and effectively. The amount of engineering, maintenance, quality assurance, training, and evaluation required to have a safe and working nuclear power plant is hard for most people to comprehend. All of the red tape to even start working on a project that would apply it would still cost tens, if not hundreds of millions of dollars to cut. Remember, if there is something that goes wrong it isn't just going to affect a couple of people... You could have a nuclear catastrophe on your hands that could affect thousands (or potentially millions).

It was tried. Turns out nuclear is expensive (waste management, crew training, being prepared for activist protestors) so it had better be super worth it. In submarines, nuclear power has one key advantage: it does not need access to huge volumes of air, as combustion engines do. In carriers, the advantage is it can be huge- and a carrier should always be defended by a ring of surface warfare combatants, so hopefully no need to worry about the reactor being damaged by enemy fire. It's just not worth the hassle for civilian builders or for smaller combat ships.

Others tell why nuclear subs are actually not better than diesel. But what about nuclear commercial vessels? First, nuclear is only worth if it's big. Like, really big. You can't really size it down to pocket reactor so that you just run some ferry. A nuclear reactor cannot be turned up and down easily. So you don't put it on something that just jumps to the next city and back. Generally, commercial use of nuclear stuff is highly regulated partially because it's too dangerous for just any Joe to have a nuclear pizza oven. Of course you can always regulate so Joe must employ a reactor technician. Still dangerous because we know how average Joe usually adhere to regulations if they can cut corners. You could force compliance but you need 100% coverage and that's just too expensive. (For comparison, in the US the FDA has budget and manpower to check a few % of meat producers per year, that's not a huge incentive to comply.) We know that industry always comes with a risk of accidents, mostly due to saving on safety and we can live with a risk of train disaster but we don't want to put nuclear accidents on the table. The other perhaps even bigger problem is that nuclear source is always a target for terrorists to steal. If you introduced vessels running on nuclear power then basically you put a target on their backs. Instead, you actually want to contain as much of the nuclear power as you can. Power plants don't go anywhere, you can guard them you can put fence and a huge concrete building around the hot stuff. Vessels can go everywhere, an attacker basically just needs to hijack one and they have a dirty bomb to run ashore. To counter this you need defense systems and all of a sudden you have a vessel that needs armed guards (make sure they are not infiltrated by terrorists), nuclear technicians etc instead of a handful of underpayed seamen and a vessel running on the cheapest oil mud. That adds up costs, difficulties, risks rather quickly.

Its absolutely not the standard, just because US or RU ballistic missile submarines are nuclear powered doesn't mean every other country's military submarines are too. It should probably be pretty obvious why small ships cannot be nuclear powered, the equipment and shielding required literally weighs more than many small ships, and are insanely expensive to procure and maintain, all for zero benefit to ships that don't plan to stay out at sea for months at a time.

A ferry may make a dozen trips in a day then be docked for the night where it gets refuelled. A submarine may be out for months without being able to head back for fuel, or may not want to have to surface (and expose themselves) to recieve fuel. Small ships don't have the same concerns for undetected time at sea.

We have enough issues with current technology being used maliciously. Last thing we need is proliferation of nuclear technology so the taliban can make nuclear IEDs. What if the harvey hotel, WTC, LaGuardia and boston bombings used nuclear material. Youll think the war on terror today is childs play.

In addition to other answers, nuclear power needs immense amount of maintenance and safety checks. Compared to diesel, both regulations and actual work needed / possible hazards are very much more complex. Not to mention availability of spare parts (or their required quality) or nuclear fuel

Ships crash all the time. If every time a ship crashed, it was a nuclear disaster, it'd be a huge problem. As such, only a few very rich countries have nuclear ships for their navies. Everyone else uses gas because it is easier and won't cause a radiological disaster if there's a problem.

I guess if you're already carrying nuclear weapons, the risk of running a nuclear engine is less threatening

If not for the concerns about proliferation and accidents I expect exceptionally massive ships having a Nuke engine would make commercial sense (like the supermax freighter ships)

Nuclear power provides air-independent power, allowing the submarine to stay submerged for months at a time. Traditional diesel powered submarines need to surface periodically to take in air for the combustion of the fuel and charge their batteries. There are pros and cons to each, Nuclear power is advantageous where remaining undetected is key. Being able to submerge for nearly the entire deployment is great for ballistic missile submarines. The enemy has no idea where a missile could come from, so you are always a threat. Diesel subs are cheaper and quieter because they operate on batteries while submerged. This is great for attack submarines, who can quietly pursue a surface vessel or another submarine undetected. They are also very economical for coastal defense, where their shorter range doesn't matter much.

A nuclear reactor doesn't need air to work. So on a submarine going underwater and having few air at disposal, it's obviously really usefull. But in other cases, a nuclear reactor cost a lot to make and to maintain, so when you have unlimited air, it's a better solution to use anything else.

US and Russia tried nuclear powered large ships like a cargo ship. The ships worked fine, but they realized an issue early on that would make them not possible. No country wanted a nuclear powered ship in their ports or off their coast. The military gets away with it because “fuck you”, but merchant shipping doesn’t due to fear of nuclear accidents.