3 ms·

I can think of a few possible answers: 1) wouldn't you just insert/remove control rods as needed to restart the nuclear chain reaction? i'm pretty sure most re

• arethuza 13y ago
  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: http://en.wikipedia.org/wiki/SL-1 http://en.wikipedia.org/wiki/SL-1
• VLM 13y ago
  #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.
  • joshAg 13y ago
    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.
    • VLM 13y ago
      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...