Finally, a HN thread that I can contribute to and I'm 9 hours late to the party.
I was serving in the engineering department on a USN aircraft carrier (non-nuclear) when a cascading casualty led to all boilers going off line. The ship had an emergency diesel generator aligned to automatically power up, but it failed to start due to a previously-unknown problem. So an 80,000 ton warship with 5,000 people on board slowly drifted to a stop, completely dark except for emergency 60's-era-battle lanterns that were already starting to dim.
No steam = no electricity (the normal ship's generators were steam-powered) and no electricity = no steam (because the start-up feedwater pumps and air blowers for the boilers were electric).
One of the other two EDGs was already down with a casualty which left a single diesel generator that had to be started with compressed air stored in two huge bottles--so basically had two chances to get the ship moving again. (No electricity = no air compressors to refill the bottles.) After a few hours of double- and triple-checking the alignment of the diesels, electrical systems, and boilers (the original steam plant casualty had to be diagnosed) using flashlights in temperatures well into the triple digits (no electricity = no air condi...you get the idea) we successfully started the one remaining diesel which provided AC to the boilers to start up.
By far the scariest day I ever had in the navy. Only saving grace was that we weren't flying planes at the time.
Could you have hacked something up using a starter cart or even an aircraft or APU or something (or a launch or cable to an escort), if the two tries had failed, but for some otherwise-corrected problem so a third try would work?
Or I guess just transported some compressed air from an escort, too -- I'm not sure what volumes you're talking about, and if the other gas cylinders a warship probably has on board would be suitable)
Presumably they have more than one of the same class of ship, which (further presumably) has the same emergency start tanks (and air pumps + power to refill them for additional tries).
Could be a loooong wait, though. I guess that's why they have two.
Square/cube law strikes again. You can only run an automotive starter continuously like a minute or so (at absolute best) before something melts down and the system is scrap. Scaling the power cube up by a factor of a thousand or so and the cooling square surface area up by a hundred or less and suddenly you get like one revolution of the motor before the starter windings and relay/contactor melt down. Not pretty. Of course you could make everything unimaginably immense but that starts making air tanks and air compressors look cheap.
I think it was because the system was simpler and more reliable with no moving parts besides valves, just a giant air bottle with pipes leading to each of the cylinders. No motor to worry about or lead-acid batteries to maintain. The whole system probably took up way more room than a starter motor would but excessive space or weight is not a big concern on an aircraft carrier.
I think it also had something to do with age - newer vessels (submarines, at least) use a large lead acid battery array for emergency power when needed... and by emergency power, I mean enough power to start the emergency diesel generator.
Submarines do have a large lead-acid battery for emergency power. In fact, the WWII-era boats had bigger and better batteries.
However the battery isn't there to start the Emergency Diesel Generator. Submarine EDGs are air started, for many very good reasons.
We still need the batteries since it's possible to suffer a loss of all AC power while the boat is submerged far beyond feasible snorkel depth, and have to recover from it without broaching.
1) wouldn't you just insert/remove control rods as needed to restart the nuclear chain reaction? i'm pretty sure most reactors design control rods to be manually insertable/removable, even if there are other way to insert/remove them
2) a standby diesel generator with good ventilation, especially passive ventilation?
3) a large dc power source (ie big, charged batteries) to "jumpstart" either a diesel generator or the nuclear reactor the way my car battery jumpstarts my car when I turn the key
4) some other form of stored potential energy and a generator that can extract it (eg: compressed gas through a turbine) to start 1 or 2.
5) (really just a subsection of 4) human powered generator of some kind. perhaps a few stationary bikes?
#1 actually no, a lot of designs have a spring pulling the rod into the core, and an electromagnet sticking to the rod, so if the plant utterly loses power the rod snaps back into the core and can't be pulled out. In theory you could attach the rods to bypass the safety feature but its just not happening.
Another issue is you run the coolant pumps to dump a couple MW into the system to reach operating temp/pressure after a day or so, THEN light off the reaction so you don't have varying steam conditions affecting the nuke physics. You don't "heat up" a nuke under nuke power as most assume. Its already thermally hot operating temp when you pull the rods.
so if i'm understanding correctly, from a black start it would take at least a day for the nuclear reactor to come online?
then you'd need at least a couple diesel generators and fuel or power cells to get the reactor into a state where it could start generating power.
Since you said megawatts, there will probably need to be a smaller generator or two to start the generators that will start the reactor, since i think MW diesel generators take a fair amount of work to get started themselves.
And we haven't even talked about backup generators in separate parts of the boat/ship in case of engine fire/damage.
Also, there would probably need to be at least another generator/power cell whose only job is to ensure that the sub can blow its ballast at any time (and of course, just regulate it) that comes up as soon as the reactor goes down.
I was mostly talking about stationary plants. You'll never get a straight story from the navy guys.
There's the slowest safest possible way to carefully test and monitor a power up guaranteed to cause minimal maint issues and longest possible life and highest safety to the civilian city downwind, and then theres OMG the missiles are flying we gotta get outta port right now. And there's numerous engineering changes you can apply to make things faster. And a tiny little 10 MW plant or whatever a sub has is a whole different kettle of fish than a 1 GW stationary plant. And the stationary plant has to care about efficiency because they're trying to pay off construction loans so any PITA that increases output is a win, but the sub boys have no (direct) loans to pay off and as long as the boat moves when the skipper says, the efficiency doesn't matter.
So they're going to be different.
But yeah, even booting up a sub is going to be some time and some work, even if you're in a hurry.
And there's historical issues like xenon poisoning which boils down to if you shut down a reactor in a "bad" state of the chemical shim system (which is kind of like intentionally dissolving a control rod in the coolant) after it was run hard and put away wet such that Xenon builds up in the core, that dude is not going critical for a day or so even if you pull the rods completely out, until the shim system cleans up the coolant... at least on land. I suppose if I was in the .mil I'd have a way to dump distilled water into the coolant for just such a situation and/or I'd have regs to never run the shim system that high and/or I'd have so much excess reactivity in the control system that, well, a landlubber would be nervous about it, so you could just burn thru the xenon poisoning anyway. And/or a regulation that says no shutting down the reactor in a rode hard / put away wet scenario so xenon would never be an issue. I mean if you're not paying for the fuel, and you're worried about xenon poisoning, one way around it is never shut the thing off, ever, unless its a major radiological issue. That's certainly one way around it.
Generally subs compress air before they need it, so there's usually plenty available before something "happens". If you're just pumping up the tanks right before you need them you've probably got serious problems or doing something completely ridiculous...
"Black start" of a sub would strictly be mid-ocean adventures which are probably classified and/or completely BS sea stories. Normally they power up off shore power while in port. I would imagine this does nothing for secrecy, the lights dim at the harbor and the backup generator is idling, hmm, I wonder whats shipping out tomorrow?
There are often no backups. The front of the sub usually isn't as sensitive as the engineering spaces and the engineering spaces aren't large. There's no snorkel coming out of the forward torpedo room so there's no backup diesel in there, besides, where would the torpedos be? I'm told by actual sub people that the front half of plastic models of subs are usually pretty realistic and usually based off completely declassified stuff, but the back half of most models is pretty much modelers artistic license time, and that's all they'll say, which I guess is how it should be...
I know the air is compressed when they flood the tanks, but I'd assume that some power is needed to blow or regulate ballast, just from a mechanical standpoint of opening and closing doors.
I'd be surprised if there were no backup generators at all. Maybe not in the front, but somewhere where the primary backups aren't. Shit happens.
Compressed air can be directed wherever it needs to go by installed piping and valves, and the valves themselves can be hand-operated.
Submarines do indeed carry an emergency diesel generator, and they also have a fairly large battery, but the emergency main ballast blow system can be run off of nothing but previously-stored energy and a hand-actuated valve.
Your mention of manual removal of control rods reminded me of the SL-1 reactor accident - where some unfortunate chap went to raise a control rod a few inches but accidentally pulled it out 26 inches - the resulting huge power surge and water hammer caused a very nasty accident killing all 3 operators:
Big ole batteries - you'd need them anyway to run systems in the first place, should the reactor be shut down at depth. It looks like something like, say, a Los Angeles class sub can actually run its generator from batteries
"[...]power can be provided from the submarine's battery through the Ship Service Motor Generators (SSMGs)."
This is a problem that the engineers designing nuclear submarines have thought long and hard about - the USS Thresher and all crew were lost in part due to inability to rapidly restart a scrammed reactor.
Everything I learned on the boat just taught me that I have so much to learn. So many minor details that a ship designer thought up went into each successive class of U.S. submarine. There were many days when I'm surprised again that we haven't lost more submarines due to design flaws or misfeatures.
Hah, that is surely one of the many differences between reading about a sub and serving on one.
Me: US navy nuclear submarines are a much-cited example of the successful design, development and deployment of high-reliability systems.
You: I sometimes wonder how it is that more of us are not sleeping with the fishes.
Still, everyone from designers to crews must be doing something right since it's apparently possible to drive such a machine into a rock at flank speed[1] or through a boat[2] or have it commanded by someone exhibiting strikingly poor judgement[3]. Without killing everyone on board and better yet, the planet.
I'm certain nuclear power submarines have two nuclear generators always running to prevent this from happening. I also think they may have a diesel powered generator for bootstrapping.
Only 1 U.S. submarine has ever had 2 nuclear reactors (bonus points for those who know why it was designed with 2).
Soviet submarines often had 2 though.
For the U.S. submarines they frequently would test shutting down the 1 operational reactor at-sea and trying to recover from the casualty, just to prove that it could be done when you didn't have time to pre-plan.
Edit: U.S. subs do have diesels though. So next question: how do you bring up the diesel engine and its required auxiliaries without AC?
Here's the black start procedure for the 1950's-era ship I worked on. No idea if this is at all similar to how they start diesels on a modern sub.
1. Hand-crank a small diesel engine connected to a small air compressor.
2. Use the small air compressor to build up pressure to start the emergency diesel generator.
3. Start the emergency diesel.
4. Using the emergency power, run one of the large air compressors to build up pressure for starting the main generators.
5. Start the main generators.
The emergency diesel was near the stern of the ship, away from the generator room, to ensure an generator room fire couldn't take out the emergency diesel.
It's actually similar on a submarine, except that there's no need to hand-crank an air compressor as we have tons of compressed air already available on a submarine.
Also, once the diesel is running it is used to power the electrical buses that provide the minimal pumps and other gear needed to recover the reactor and eventually restart (or emergency restart) the turbogenerators that provide ship's service power.
Unfortunately there's no room to have separate emergency generators and emergency diesel so they are co-located.
I skipped quite a few in fact. I love getting people interested in submarines but I have no great desire to irritate my friends at NR by creeping past the rules regarding NNPI (whether of the U variety or otherwise).
I can appreciate that. And I was just having a little fun with you.
But I was simply referring to the part where you surface the boat before starting the diesels. I think some folks might be under the impression that you can run those while submerged which is most decidedly NOT the case.
What I think many people don't realize is that a reactor shutdown is likely to be a mission-over/career-ender type of deal for almost the entire officer corps onboard. It's not supposed to happen EVER. It's like forgetting your gun as you exit the helicopter.
BTW, It was "supposed to work" but didn't isn't an excuse. You (as an officer) are responsible. That's what maintenance and drills are for. Reactor shuts down and diesels won't come up? Wow. Major UNSAT. A dead-in-the-water carrier is almost as bad as running the damn thing aground.
I'm wondering how the CNO felt about that poodle-screw.
You can run the diesels underwater though. Obviously there is a limit, but surfacing the boat is neither required (sea state permitting) nor desired ("OH LOOK, A SUB!!").
DIW on a CVN is a big deal, that is true (though hardly a career killer by itself for O-gang, even the ones in Reactor Department). NR takes nuclear safety very seriously and the carrier won't sink just from loss of propulsion so the reactors will very much be configured to fail conservative if necessary.
Even on a submarine, which can flounder without propulsion and only has a single reactor, we do scram drills all the time. A scram can occur for no better reason than that reactor protection was feeling finicky that day, so the drills are designed to assume a scram will happen, and recover safely and efficiently.
On the other hand, an unplanned scram really is one of those things which may get someone disqualified from watchstanding, and possibly de-nuked completely, since those usually represent a crew that doesn't properly respect the power of the reactor.
I don't know that I'd call running with the snorkel up anything but non-submerged. Although I will give you that running at p-depth is almost the same thing. I'm sure you'll agree that anything other than underway on main propulsion is a far less preferable situation than normal ops.
BTW, I spent some time as a bubble-head, so I do understand what you're talking about here. Just keep in mind that not everything you've heard about subs is true and not everything I knew about subs is still true. A lot has changed since I was in.
Technically, you mean the only USN SSN with two shafts, but even that is incorrect. Nautilus was a conventionally-driven submarine with counter-rotating screws just like its diesel-electric WWII-era forebears.
The first single-shaft U.S. submarine was a diesel research vessel, USS Albacore, which proved the feasibility of many innovations which were later ported over to the nuclear submarine fleet. USS Skipjack was the first nuclear submarine to include most of those features, including single-screw design.
Never been in the navy, so just guessing. Just kicking around ideas...
Option A: You hand-crank the beast somehow? To get the glow-plug going, you again use a hand generator? Hopefully enough to bootstrap the generator (maybe it's a smaller generator that runs a larger one)? Generators all the way down?
Option B: You blow ballast somehow and use the inrushing water to drive a turbine that runs the generator or gets it going?
Option C: You manually pull the control rods and switch the coolant loop to run a small turbine to prime the generator?
Option D: You mayday and get a jump from the Russian/Chinese/Iranian sub following you around?
Option E: You try something dumb and dangerous with hydrogen peroxide from the torpedoes (I think/hope that that's phased out now)?
I think it's mostly batteries, a sub operating at constant depth and in motion is negatively buoyant. If something goes wrong and it loses propulsion, power has to be available immediately to operate the systems that can handle the emergency - whether it's blowing ballast or restarting the reactor. This is a somewhat different constraint than the procedure described by the other reply - ships float without power, subs, not always.
I mentioned this upthread - USS Thresher[1] seems to have suffered a loss of both propulsion and ballast control while near test-depth with, unfortunately, tragic results for the vessel and all on board.
Option F: Compressed air. Turns out mechanical systems are stupid simple to hand-power and yet can store a ton of energy usable without fancy equipment. Plus it turns out we might need compressed air for this no matter what depending on where the boat is at.
All merchant ships are required to have enough compressed air for several starts (and we're talking about much larger diesel engines). I'd assume it's the same for a nuclear sub.
With a storeable dc power source, just like a car or truck.
I suppose if that failed or had somehow discharged incorrectly, there should probably be a way to handcrank the diesel generator, like how early cars required hand cranking to start.
PS: I had to look it up, but that's an interesting reason why that us sub had 2 nuclear reactors.
That was the most interesting part of this article. Even the largest power plant comes down to a simple 12V battery needed to bootstrap the first generator.
You can't confuse acetylene or nitrogen, old or new style; acetylene uses maroon for the whole bottle, nitrogen uses black for the shoulder only. Also the cylinders are quite different shapes.
Also the colours are for "the room is on fire, quick what's in that gas bottle over there?" situations. Are you allowed to be a safety responder if you're colour blind? For everyone else the rule is pretty simple; GTFO, and if acetylene is involved, GTFO out of the postcode.
