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Old 11-11-2018, 02:12 PM   #11
malloyd
 
Join Date: Jun 2006
Default Re: DIY Nuclear Reactors After the End

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Originally Posted by Ulzgoroth View Post
Though you don't actually have to achieve criticality to produce usable power. A safely sub-critical reactor pile would require a lot more mass and especially a lot more fissionable material than a proper reactor of the same power, but is a much easier engineering task if you somehow have enough material for it. (Essentially a giant RTG.)
RTGs only work because the isotopes have a really short half life - i.e. they decay fast enough they're generating significant amounts of heat. This means natural sources are very diffuse (since they are only around as short lived decay products in masses of something much more stable that has lasted long enough to form ore bodies) and hence ridiculously expensive to refine.

You're a little better off in the near term post apocalypse, since there are still chunks of artificially enriched or produced isotopes around - if you don't care about killing your workers you can pull spent fuel rods out of their storage pools and stick them in smaller volumes of water that will get much hotter than the pools do - the stuff sitting around in pools at most nuclear plants will probably be producing several percent of the heat output of the operating plant for decades, but even high level nuclear waste has quite a limited supply, and it's too "short-lived" a resource for more science-fantasy settings, a century or two on and even it's too dilute to be very useful.
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Old 11-11-2018, 02:49 PM   #12
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Default Re: DIY Nuclear Reactors After the End

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RTGs only work because the isotopes have a really short half life - i.e. they decay fast enough they're generating significant amounts of heat. This means natural sources are very diffuse (since they are only around as short lived decay products in masses of something much more stable that has lasted long enough to form ore bodies) and hence ridiculously expensive to refine.
A sub-critical mass can still undergo fission much faster than the natural half-life of the isotope, though.

Obviously, yes, sourcing the fuel for that is unlikely to be feasible in ATE contexts unless you're burning through a pre-fall stockpile of refined material.
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Old 11-11-2018, 03:12 PM   #13
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Default Re: DIY Nuclear Reactors After the End

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Edit: If you want a settlement to have locally produced electric power, I really recommend either hydroelectric, or (wood or coal fired) steam engines, both of which are scalable all the way down to projects individual hobbyists or off-grid fanatics, can and do put together themselves with parts well within the reach of a small machine shop. Even getting nuclear fuel is hard - there's a reason we haven't had a terrorist movement or even small civil war deploy a nuclear or radiological attack yet.
Another option is wind power. It's not reliable, so you'd use it to charge batteries on a small scale and to run industries that can use power when it's available and don't need a constant supply (making things in batches, etc.). Supplement it with hydroelectric power to run the stuff that needs a constant supply, and coal/wood if that's not enough.
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Old 11-11-2018, 03:20 PM   #14
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Default Re: DIY Nuclear Reactors After the End

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A sub-critical mass can still undergo fission much faster than the natural half-life of the isotope, though.

Obviously, yes, sourcing the fuel for that is unlikely to be feasible in ATE contexts unless you're burning through a pre-fall stockpile of refined material.
I think at this point you're looking at getting a few fuel rods from a pre-ruin reactor or waste facility, and having someone you don't care about carefully push them closer and closer together until they're hot enough to boil water. You then have yourself a boiling water reactor, and the rest of the system is a straight-forward steam plant. The problem is that if it ever runs out of water, you have a meltdown and no more plant. Another problem is that the thing is going to be killing workers fairly regularly, and probably contaminating whatever watercourse(s) you're dumping your coolant and working fluid into.
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Old 11-11-2018, 03:36 PM   #15
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Default Re: DIY Nuclear Reactors After the End

There are alternatives.

IIRC a Nuclear Reactor is basically a kettle to heat water to produce steam to turn a vane connected to a generator.

A generator is more or less magnets and wires to generator electrical current that can be utilised by a motor or light bulbs etc.

Wind and Water power would more likely be easier methods of generating power.

Of course depending on the size of the generator would depend on the power required to turn it to produce power. This may then return the question back to the nuclear option.
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Old 11-11-2018, 03:58 PM   #16
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Default Re: DIY Nuclear Reactors After the End

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I think at this point you're looking at getting a few fuel rods from a pre-ruin reactor or waste facility, and having someone you don't care about carefully push them closer and closer together until they're hot enough to boil water. You then have yourself a boiling water reactor, and the rest of the system is a straight-forward steam plant. The problem is that if it ever runs out of water, you have a meltdown and no more plant. Another problem is that the thing is going to be killing workers fairly regularly, and probably contaminating whatever watercourse(s) you're dumping your coolant and working fluid into.
If you run out of water, you have someone expendable whack the fuel rods a bit further apart with a fireplace poker before they get hot enough to melt.

Obviously that isn't a perfectly reliable procedure, but it's something.
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Old 11-11-2018, 04:10 PM   #17
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Default Re: DIY Nuclear Reactors After the End

I have seen proposals for what's basically artificial geothermal energy by just dumping a large amount of radioactives (probably nuclear waste) down a hole large and deep enough to be well insulated (for example, dig a hole and drop a nuke down it), letting it heat up, and running water pipes through it. This is probably something that you could do AtE if you happened to have a large amount of radioactive waste (say, Yucca Mountain ever actually gets completed) though it's certainly a temporary thing (if you have a large enough blob, it will remain hot considerably longer than the high level wastes, but not forever).
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Old 11-11-2018, 04:22 PM   #18
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Default Re: DIY Nuclear Reactors After the End

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I have seen proposals for what's basically artificial geothermal energy by just dumping a large amount of radioactives (probably nuclear waste) down a hole large and deep enough to be well insulated (for example, dig a hole and drop a nuke down it), letting it heat up, and running water pipes through it.
That's a rather clever response to the environmentalists screaming that residual heat will be warming stuff for kilometers around the burial site for centuries. If it actually ever gets hot enough to be a problem, it's a valuable resource instead.
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Old 11-11-2018, 08:31 PM   #19
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Default Re: DIY Nuclear Reactors After the End

Does it have to be made after the end? Can a settlement stumble upon a hidden, automated, underground reactor from before the end of the world that’s still running on autopilot and decide to use it as their own?
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Old 11-11-2018, 08:55 PM   #20
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Default Re: DIY Nuclear Reactors After the End

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That's a rather clever response to the environmentalists screaming that residual heat will be warming stuff for kilometers around the burial site for centuries. If it actually ever gets hot enough to be a problem, it's a valuable resource instead.
Not really, since as a response it doesn't address environmental concerns in any way. And might not even be true, depending on how much warming constitutes a problem.
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