Is Reprocessing the Answer?

Andrew Mason

My understanding is that the IFR would greatly reduce both the quantity of waste and the length of time the waste would have to be stored (since the ultimate waste is short lived fission products that would only need to be securely stored for a few hundred years).

However, this recent article in the Bulletin of Atomic Scientists seems to suggest that even the Integral Fast Reactor (IFR) model does not present a solution to radioactive waste.

Is the author correct?

AM

joelupchurch

The short answer is no, he isn't correct. He seems to think that the disposal problems of fission products that have half lives in decades are equivalent to actinides measured in 10s of thousands of years. When you only have to secure the fission products for 300 years, then almost any approach will work. Also there is a huge reduction in the volume of the waste to a few grams per person per year. We are talking about 1 ton per gigawatt-year compared to 20 tons of spent fuel for the same amount of power from a LWR.

It's possible that a Thorium breeder reactor would be cheaper to build and operate than an IFR, but the waste disposal issues are similar.

Andrew Mason

I am not sure he does not recognize that because he does acknowledge that fast reactors would use up the higher actinides. He does not make it clear why a long term geologic repository would be needed:

He seems to be saying that not only is reprocessing not a solution to spent fuel storage for LWR reactors (which is probably correct) he seems to be saying that reprocessing is not economical for fast reactor fuel and, in any event, it doesn't alter the need for long term geologic repositories.

That is what I thought too. Garwin certainly does not make it clear that there is a huge difference between, on the one hand, storing the ultimate waste from a fast reactor (eg. IFR) which is short lived fission products, and, on the other, spent LWR fuel including spent MOX fuel. There is a huge difference in volume of waste and longevity.

He also does not mention that fast reactor fuel can be designed for reprocessing, such as the IFR using metal fuel that can be reprocessed using electro-refining techniques (I am relying on Morbius on this) and can be made much more economical to reprocess than reprocessing LWR uranium oxide fuel.

AM

vanesch

I think it is indeed safe to say that one will need a repository in any case. You cannot hope to burn up to the last atom of actinides or of plutonium - some waste will always occur. Also, even 300 or 500 years is a long time. So better bury it. What is true, is that the geological requirements of the repository are much less severe, because most of the confinement problem can be handled by human barriers, and what will diffuse into the geology is way smaller than with no reprocessing and no fast reactors. The consequences of a "leak" in 1000 years are much smaller.

joelupchurch

I discussed the issue of decay products with Kirk Sorensen over at EnergyFromThorium. He attached a useful chart of the decay products.



A lot of them are useful and it would be foolish to throw them away. We might need them badly down the road. I also asked him if some of the radioisotopes might have immediate applications and got this response:

Sr-90 and Cs-137 are probably the most useful radioisotopes in the mixture. They're also the bulk of the radiotoxicity from the fission products for the 300 years after discharge. Mo-99 (decaying to Tc-99m) would be very useful if you could get to it quickly, because Tc-99m is used in so many medical procedures. It's impractical to harvest Mo-99 from solid-fueled reactors because of its short half life, but LFTR would be different because Mo could be removed rather easily through fluorination (MoF4 -> MoF6).

Also, if it's Sr-90 you're after, LFTR could end up making much "better" Sr than LWRs. That's because only about half of the Sr in typical LWR fuel is Sr-90. The rest is Sr-89 and Sr-87, which are both stable and inert (if I remember correctly). In LFTR, the precursors to Sr-87 and Sr-89 are both gaseous Kr-87 and Kr-89, which will get swept out by the off-gas system. The Sr left behind in the reactor could be upwards of 90% Sr-90.

Xnn

Guess I don't see what the problem is with our current practices.

Put spent fuel (dry) into a sealed metal canister and the cannister into a concrete block.
The concrete block sits on a level pad the size of a small parking lot.
And then it just sits, surrounded by barbed wire and security guards
with not much else to do. If we had to, we could truck it some where, but otherwise it just
sits around until we either re-process it or decide to bury for the longer term.

It doesn't leak, it doesn't rust and eventually it's not even warm as rad levels continue to drop.