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Nuclear Geothermal Power

Nature does it, so why not us?
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Today most of the heat coming out of Planet Earth's depths ("geothermal energy") originated from radioactive decay of various substances. In a sphere more than 12,000 kilometers in diameter, even a small percentage of uranium, thorium, potassium-40, and other unstable atoms in the mix adds up to a tremendous total quantity. A fraction of that is always breaking down, releasing nuclear energy which, by the time it reaches the surface, has transformed into ordinary heat.

There are places where we can conveniently tap that energy to generate power. Most of them feature a place where heat is coming out of the Earth somewhat faster than the average location, plus an abundant supply of groundwater, which that heat boils. Hmmmmm......

Let's take a largish piece of unused desert terrain and draw a 10-kilometer diameter circle on it. Next, all along that circle, we need to dig down pretty deep, maybe 3km, and install a flexible impermeable barrier. We'd like the local underground geology to be mostly impermeable, too (which makes installing the barrier more difficult; igneous rocks can be tough to penetrate.) That's the most expensive part of this Idea, probably, but it is the environmentally responsible thing to do.

Next, in the center of the circle, drill down maybe 3km and plant an appropriate nuclear bomb. This is not a Test, and so should not be in violation of the Test Ban Treaty. When the bomb explodes, the shock waves will crack and break a considerable amount of the surrounding rock. It can even compress rock and create a chamber, which then tends to collapse. Close to the surface, as observed during many tests, the collapse will lead to a depression in the ground, but we want THIS bomb to be too deep and not big enough to cause that.

Next, in many places inside the 10km circle, not terribly far from the center, drill down say 2km and prepare to pump water down half the shafts. It will permeate the cracked and broken rocks and can be pumped out again through the other shafts. But we don't do that second thing just yet, because ONE nuclear bomb isn't really enough for this Idea.

We need a special "plug" that can be placed in the shaft we drilled to emplace the first bomb. The bottom part of the plug will of course be destroyed by the blast, but the rest we would like to be able to remove fairly easily, so we don't have to drill through it, to plant another bomb. We would only need to drill through the bottom/destroyed part of the shaft-plug.

Most of the energy of the first bomb was expended by shattering a lot of surrounding rock. Now the second bomb is placed in the midst of that, and we have filled the cracks with water. THIS bomb will boil a LOT of water. So will the next bomb, and the next one, and the next one....

We now extract very hot water from the ground, just like we were dealing with a natural geothermal energy location. We use it to generate power, converting a lot of "swords" into used-up "plowshares" in the process. This water will be carrying a lot of rather radioactive dissolved stuff in it, but that's OK, since we recycle it by pumping it back into the ground. See why we need a FLEXIBLE impermeable barrier surrounding the site? It won't crack, and it will confine the radioactivity.

This Idea may not be original with me; I'm not sure if I once read about it somewhere and am only now remembering it. However, it is not widely known, so it perhaps may be allowed to persist here at the HalfBakery.

Vernon, Jan 03 2009

Metallic fusion Metallic_20Fusion
Fusion, explosions, what's not to love? [bungston, Jan 05 2009]

[link]






       wow. I don't think annotation will improve this idea at all. I hope everyone agrees.
WcW, Jan 03 2009
  

       I agree. Annotation is hardly ever useful. It usually starts with a complete derailment from the original topic and proceeds into Monty Python jokes and so forth.
Bad Jim, Jan 03 2009
  

       Bombs are not particularly more efficient or anything than using the exact same amount of fuel in a normal nuclear reactor.   

       So... why is this a benefit over a regular nuclear reactor? It's messier and harder to control, and it would be much more expensive to set up, since your huge shield would use a lot more material than a normal plant, and this special flexible material would be fancier than concrete.
Smurfsahoy, Jan 03 2009
  

       //So... why is this a benefit over a regular nuclear reactor?//   

       Presumably the abilty to use nuclear fusion, which has so far eluded scientists except in the case of the hydrogen bomb.   

       Of course, the primary motivation for using fusion as a power source, is it doesn't create nasty byproducts, an argument which does not hold if you are repeatedly detonating nuclear bombs.
Bad Jim, Jan 03 2009
  

       If you're talking about typical radioactive byproducts, it had also better be a durable shield, as they aren't going to go away any time soon.
The other issue is the nature of explosions underwater. While much of the water would vaporize I'm not sure this would improve anything, and even if so I suspect the shock-wave would travel well ahead of the thermal energy. As such, unless there is a lot of air space in the detonation chamber, each successive detonation is going to fracture out a larger and larger space, eventually creating a chamber that either breaks through to the surface and thus probably becomes unsealable, or breaks through the crust entirely, creating a volcanic hot spot that would likewise send your controlled radioactive material through the upper surface of your detonation chamber. I would think the former at 3km deep, but an air gap above the detonation pool would tend to transmit the shock downward exclusively, so it might be the latter.

Admittedly, in the latter case, once the radioactivity cools off in a couple thousand years, you would have a very nice natural geothermal site all ready for use.
MechE, Jan 04 2009
  

       [Bad Jim], yes, I should have specified fusion bombs in the main text. I'm aware that they are triggered by fission bombs, but most of the energy released does come from fusion, so that is why they are called fusion bombs.   

       [MechE], depths such as two and three kilometers are specified so that the blasts and the radioactive consequences are completely contained. Any reasonably flexible classic plastic (such as thick low-density polyethylene, the stuff Tupperware is made of) will work fine as the barrier, we just need a lot of it. Remember how environmentalists complain about how classic buried plastics can last for thousands of years? We will be using that here! And placing this barrier 5km from the blast site has the purpose of keeping it reasonably unexposed to heat and radiation and shockwave damage; its main purpose is to ensure groundwater doesn't get past it. Note that if groundwater doesn't flow, because it is blocked by a barrier, then it mostly doesn't flow toward the barrier, either. Radioactive dissolved stuff will only SLOWLY creep toward the barrier.   

       Next, broken rock will act as a pretty good shock absorber for blasts that follow the first blast. Remember that sand, super-broken rock, is used as a vibration-damping substance. And the rocks' absorption of shock waves will be convert that energy to heat, of course. I'm fairly confident that all the subsequent blasts can stay contained, provided they are deep enough (the 2km is an estimate). We also have the option of filling the first chamber created by the first blast with sand or gravel, specifically to reduce the effectiveness of blast-transmission through gases in the chamber. The vertical borehole through which the first bomb was planted, and through which we want to plant the next bomb, will of course enter the top of the chamber....
Vernon, Jan 04 2009
  

       Wow there is some seriously bad science in here. And bad ethics. Well...and bad engineering and....well ya know this idea is just plain bad.   

       Why not simply drill a bunch of geothermal wells, you would generate an equivalent or greater volume of power without any of the costs or consequences.
jhomrighaus, Jan 04 2009
  

       please. this isn't helping.
WcW, Jan 04 2009
  

       This idea reminds me of the recent idea posted by an HB newcomer, who proposed to generate a fusion reaction in liquid hydrogen and capture the explosively emitted energy with a lot of water. Linked.   

       Vernons iteration or the "capture energy from fusion explosiun" uses more proven technology except from the superdeep hole. The deep hole is really not necessary for this to work - one could do it less deeply with smaller bombs.
bungston, Jan 05 2009
  

       [bungston], the problem is that fusion bombs generally are much more powerful than fission bombs, and so if we want to use this Idea to get 'controlled fusion power', it is sort-of mandatory that we use deep-enough holes to make sure those big blasts are contained. Most underground nuclear tests only involved fission bombs, IIRR.
Vernon, Jan 05 2009
  
      
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