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.
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?
Remember, it's called the silent service for a reason. Those who know, don't tell; those who tell, don't know.
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.
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 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.
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.
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.
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.
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.
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.
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.
http://void.printf.net/~conor/sa/LHCb/LHCfuel.jpg
Without that insignificant-looking bottle the whole machine would have nothing to do.
(Edit: I do have to wonder how wise it is to paint a bottle of hydrogen to look like a fire extinguisher.)
That's not even getting into the whole red-green color blindness issue that could lead to confusing 'Flammable' with 'Inert' contents.
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.
If the room's on fire and I'm in it, I'm a 'safety responder' whether I want to be or not.