As the title says; why can’t we just melt down the old fuel rods?
What would happen if we did melt them down?
Couldn’t we mix/contaminate them with another element to dilute the radioactive effects?
Most reactors work by heating water and turning turbines, why can’t we turn the spent fuel pools into a slow running reactors rather then using energy to keep them cool?
In: Physics
Spent fuel is extraordinarily radioactive. Also it’s not like a single solid material. You have zirconium cladding, which is the shell. Inside is fuel material, the ceramic fuel pellets. But you also have fission products, you have radioactive gasses, and all sorts of nasty stuff as a result of the random process of splitting atoms.
The radioisotope inventory is ridiculously high in the fuel rods. Melting them means breaking the zirconium shell that prevents lethal amounts of radioisotopes from escaping.
The spend fuel rods will be highly radioactive for millennia but will only generate heat so you need do cool them in spent fuel pool for 10 to 20 years.
The heat output is not that high so non have used it to produce power likely because the cost of the stuff you need is to expensive and would complicate thing and and increase the risk of a accident so it is not done.
The fuel rods can be reused where you remove the radioactive elements that is produced for storage and extract the uranium for new fuel rods. That is called [Nuclear_reprocessing](https://en.wikipedia.org/wiki/Nuclear_reprocessing). Part of the problem with it is that is how you extract plutonium for nuclear weapons so nuclear reprocessing contribute to nuclear proliferation ie the spread of nuclear weapons and what is needed for them. So today there is only plants in countries with nuclear weapons and fuel from other countries are reprocessed in som of them.
We do have some reactors that can use spent fuel, but it does get to the point where enough energy just simply isn’t produced. The other problem is that spent fuel needs stored somewhere where it can cool effectively and not spill radiation into the area. Fuel rods are dangerous to any living thing in their area. Risk plays a role in how we deal with them too. New reactors are able to use spent fuel though. That helps reduce some of the waste.
Fuel rods aren’t simply one kind of material to just melt down.
The easiest way to reduce their radioactive effects is to put them in a shielded location that people have minimal access to.
When they are spent, sure they do produce some heat, but not even close enough to produce steam to drive a turbine.
Sure, we could. However, there is a tiny problem. One of the radioactive byproducts is Plutonium. Melting spent fuel rods has to be done in a way that doesn’t facilitate the separation of this Plutonium and using it to make nuclear weapons. That’s increasingly difficult to convince the whole world you are doing. So, most of the time reprocessing isn’t done.
I will try to explain what is currently being done in France. Most of the spent fuel is firstly cooled done for a while in actual pools of water. (water is a great biological barrier). After that it is sent to a reprocessing plant where the fission products (aka all of those elements that are “useless”, usually beta decayers) are separated from the plutonium and the uranium. Successively Pu and Uranium are also divided, by using very acid environments and complicated chemistry.
The Pu and the Uranium can then be utilized in a second cycle, in the form of MOX fuel, which is simply a ceramic fuel that contains a specific mixture of Pu and Uranium.
Problem is, when the MOX fuel is irradiated in the 2nd cycle, things get tricky, there’s a lot of bad radio isotopes that are being generated via neutronics capture, like Pu241, Am241 and Cm243. And handling these isotopes becomes very very fucking hard, especially in industrial scale.
That is why, it was decided not to deal with irradiated MOX and dissolve it into a vitreous compound.
The real hope would be being able to reutilize this fuel, but Generation IV reactors are still too complicated to be built, so governments are opting for geological depositorises for now. Hope that answers your question.
The best option is to just take spent rods and consolidate the nuclear material back into a usable rod, but a lot a people don’t want to. For fear of this technology falling into terrorist hands. So now the US is up a creek with out a paddle as the spent rod pools are over capacity, and Obama put the kabash on the Yucca Mountain site.
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