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Thread: Question on Nuclear Reactor Cooling Cycle

  1. #1 Question on Nuclear Reactor Cooling Cycle 
    Forum Freshman tdellaringa's Avatar
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    Hello,

    I write a Sci-Fi comic, and I've come here before for help and you all have been great, so I have another question. Here's the quick summary:

    Martians live underground on Mars, and there they have a nuclear reactor that provides power to the settlement. Let's assume it's somehow a little more advanced than what we do, but not much.

    The settlement lies next to an underground river, so they have a water source.

    I've read a bit from these two sources:

    Cooling Power Plants
    http://www.world-nuclear.org/info/co...ts_inf121.html

    Got Water UCS Brief (note: PDF file)
    http://www.ucsusa.org/assets/documen...-got-water.pdf

    The PDF has a nice graphic on the first page that I figure is what's going on - they superheat the water under pressure, it gets into the steam generator, where steam bleeds off somehow and powers the turbine, and they add a smidge of water back in after condensation to keep the whole system running.

    In my story, this alien who is supposedly a "technological wizard" from an advanced race tinkers with the reactor. Unfortunately when this guy "improves" something, invariably something goes wrong! In this case, I've made up the fact that his "improvement" (whatever it is) has resulted in more power output, but also more heat output - to the point where the water cooling can't handle it.

    This is where I fall apart. Questions:

    • Is it possible that a reactor could get so hot to overwhelm the water under pressure like that? If so, what would happen?

      And then, in what way might that problem be solved?


    Keep in mind this stuff doesn't have to be necessarily scientifically sound. It's an all ages comic. I like the stuff to be grounded in real science if possible - essentially I try to make certain things "plausible" I guess. I try no to do too much "Star Trek Science" if you know what I mean, but it does happen.

    Maybe I'm barking up the wrong tree, too. Essentially, I need a problem that results from more power output from the reactor, and then some kind of neat solution that might fix it.

    Definitely think outside the box and be creative, and keep in mind it has to be reduced to simple principles.

    Thanks for any and all help anyone can provide!


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  3. #2 Re: Question on Nuclear Reactor Cooling Cycle 
    . DrRocket's Avatar
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    Quote Originally Posted by tdellaringa
    Hello,

    I write a Sci-Fi comic, and I've come here before for help and you all have been great, so I have another question. Here's the quick summary:

    Martians live underground on Mars, and there they have a nuclear reactor that provides power to the settlement. Let's assume it's somehow a little more advanced than what we do, but not much.

    The settlement lies next to an underground river, so they have a water source.

    I've read a bit from these two sources:

    Cooling Power Plants
    http://www.world-nuclear.org/info/co...ts_inf121.html

    Got Water UCS Brief (note: PDF file)
    http://www.ucsusa.org/assets/documen...-got-water.pdf

    The PDF has a nice graphic on the first page that I figure is what's going on - they superheat the water under pressure, it gets into the steam generator, where steam bleeds off somehow and powers the turbine, and they add a smidge of water back in after condensation to keep the whole system running.

    In my story, this alien who is supposedly a "technological wizard" from an advanced race tinkers with the reactor. Unfortunately when this guy "improves" something, invariably something goes wrong! In this case, I've made up the fact that his "improvement" (whatever it is) has resulted in more power output, but also more heat output - to the point where the water cooling can't handle it.

    This is where I fall apart. Questions:

    • Is it possible that a reactor could get so hot to overwhelm the water under pressure like that? If so, what would happen?

      And then, in what way might that problem be solved?


    Keep in mind this stuff doesn't have to be necessarily scientifically sound. It's an all ages comic. I like the stuff to be grounded in real science if possible - essentially I try to make certain things "plausible" I guess. I try no to do too much "Star Trek Science" if you know what I mean, but it does happen.

    Maybe I'm barking up the wrong tree, too. Essentially, I need a problem that results from more power output from the reactor, and then some kind of neat solution that might fix it.

    Definitely think outside the box and be creative, and keep in mind it has to be reduced to simple principles.

    Thanks for any and all help anyone can provide!
    Thermodynamically, the energy output from a turbine comes from the difference between the temperature of the input stream and the temperature of the output stream, so the modification that you describe might have come from higher steam temperature. That could create a heat dissipation problem -- though the guy making the change would consider that if he were competent.


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  4. #3  
    Forum Freshman tdellaringa's Avatar
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    Well, the guy isn't exactly competent He has access to all this knowledge, but little or no experience. So he could (and does) make mistakes. But I should have mentioned that there are other Martian scientists around who come by when this happens, and they don't know how to fix the problem either. And *they* would know something like that, probably, because they are highly competent.

    So an ideal idea here would be something kind of strange or unlikely, that would cause a real problem.
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  5. #4  
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    This is the kind of scenario that nuclear engineers plan for regularly. If the power increases beyond what the reactor is designed for, the first thing is to stop the nuclear chain reaction by inserting control rods, which absorb the neutrons. The increased neutron flux, and the rising pressure, would be detected by instrumentation and the control rods would be released to fall into the reactor core. Chemical poisons like boric acid can also be pumped into the reactor so as to absorb neutrons and shut down the chain reaction.

    Even after the chain reaction is stopped, though, there is still heat being generated in the core. This is due to radioactive decay of the fission products and is perhaps on the order of 7% of the heat of the reactor. So the heat still has to be removed by an auxiliary feedwater system which boils water in the steam generator. The turbine being shut down, that steam would just be dumped to the atmosphere to dissipate the heat. If that fails (perhaps because somebody left the auxiliary feedwater valves isolated, like 3 Mile Island), then the pressure will rise and a relief valve will lift, and you will have to inject more water into the primary system.

    Narurally, there are a lot of other things that can happen, but this probably gives you a general idea.
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  6. #5  
    Forum Freshman tdellaringa's Avatar
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    Hm, so is the idea of too much heat not a good one? Somehow I need him to put the whole settlement in danger by "improving" the reactor. The Martians were an advanced civilization (say 30-50 years ahead of us) when they built the reactor. So like you say, they'd probably know how to handle the extra heat.

    I actually have it as sort of a mini-reactor. It's contained in a fairly small room and gives power to a fairly small settlement. Maybe a couple thousand.

    I'm open to other ideas for sure.
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  7. #6  
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    Well, if you want some ideas on how to destroy a nuclear reactor, you could read up on the Chernobyl accident. The operators really didn't understand the design of the reactor. They needed to run a test, but it had to be done at a certain power level. As they were shutting down the reactor, they missed out on their chance to run the test. They bypassed some of the safety features that would have automatically shut the reactor down and prevented them from doing the test. Kaboom.
    http://en.wikipedia.org/wiki/Chernobyl_disaster
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  8. #7  
    Forum Freshman tdellaringa's Avatar
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    Yes, I actually read about that. Pretty scary (and sad) stuff. The idea here though is this guy actually "improves" the reactor. He does in fact make it better, there's just a bad side effect. (His character plays out like that - his good deeds have consequences that need to be dealt with.)

    Maybe heat is a bad idea. Maybe there's some other side effect that could be just as bad? I'm just looking for unique, creative ideas. They don't necessarily have to be scientifically sound.
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  9. #8  
    . DrRocket's Avatar
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    Quote Originally Posted by tdellaringa
    Yes, I actually read about that. Pretty scary (and sad) stuff. The idea here though is this guy actually "improves" the reactor. He does in fact make it better, there's just a bad side effect. (His character plays out like that - his good deeds have consequences that need to be dealt with.)

    Maybe heat is a bad idea. Maybe there's some other side effect that could be just as bad? I'm just looking for unique, creative ideas. They don't necessarily have to be scientifically sound.
    He hires his mother-in-law, a wicked witch, to monitor the control rods and optimize performance.. But some flying monkies dowse her with a bucket of wateer, melting her into a puddle, only her shoes remaining. The uncontrolled reaction goes critical, threatening a melt-down.
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  10. #9  
    Forum Freshman tdellaringa's Avatar
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    I think some of those characters are trademarked!
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  11. #10  
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    Quote Originally Posted by tdellaringa
    Hm, so is the idea of too much heat not a good one?
    You might be able to make that idea work. A nuclear reactor can be made to put out more power than it was designed for, but that would make it more dangerous. Maybe your alien makes some modification to the turbine to get more power, but doesn't worry too much about the safety margin of the reactor. When the reactor runs at higher power the fuel rods are getting hotter. If they get too hot, the metal rods could melt, releasing the radioactive material. Maybe there is some kind of transient. The turbine trips off and the reactor trips as it was supposed to do. But since they were already running at too high a power, the temperature increase from the transient is enough to melt the fuel.
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  12. #11  
    Forum Freshman tdellaringa's Avatar
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    Thanks for the suggestion!
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  13. #12  
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    they superheat the water under pressure, it gets into the steam generator
    Then you're describing a pressurized water reactor. In a boiling water reactor (OTOH) the water boils in the reactor in the nucleate boiling regime to remove heat rapidly from the fuel elements. If the heat flux increases too much the boiling regime can transition into film boiling which is far less efficient at heat removal and the fuel element can melt. The boiling crisis threshold is called DNB, for Departure from Nucleate Boiling.
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