The purpose of a reactor is to heat up some fluid which will be used to ultimately drive a generator. From this thread I gather that spent fuel is still very hot (nearly the melting point of the fuel) The problem is that it cannot sustain criticality. I still don’t know why it can’t be used to drive a generator while we’re waiting around for it to cool off.
On a related note, if the US were to keep reactor waste in temporary storage rather than moving it to Yucca Mountain or wherever, how much waste in terms of mass and volume will be accumulated in the next 40 years?
Temperature is not the same thing as power. If you tried to suck power from the spent fuel it would cool off very fast. Think of it this way: if you put a teapot on a hot stove burner on high, it will eventually boil. But if you heat the burner up red hot, turn the power off, and then put the pot on, the water isn’t going to boil.
One argument is that today’s useless, dangerous crap to be disposed of might be discovered to be very useful stuff in the future…so put it where it can be recovered should the need arise.
It depends on the power history of the fuel and how long it’s been since it was at power, but typically you be looking at 100 kilowatts per metric ton of Uranium initially in the pool. After five years it would be around 2 - 3 KW/MTU. A 1000 MW reactor would generate roughly 100 MTU spent fuel over five years.
The spent fuel does generate some power, but the cost of recovering it would far exceed its value. The people running these things aren’t dummies, it would be done if it was worth doing.
One of the waste disposal options for high level radioactive waste is to stick it nice and deep in a borehole in granite (in the middle of a continental sheet). The initial decay heat is enough to melt and flow the granite around the canister, then as it cools the granite recrystallises, entombing the waste in a solid granite mass, until the continental mass is recycled by tectonics.
Of course, this waste can never be recovered for reuse. And it has to be hot, high level waste. And the drill zone must be conpletely stable geologically.
The problem with subduction zones for disposal is that we don’t really know what happens underneath the crust. You can’t drop radioactive waste into a subduction zone only to have a volcano blow it all back out a couple of years later (radioactive lava - yum) because we don’t understand how things really work.