Can Plutonium from a Reactor be Reused?

[renigade666]

The plutonium that is produced in a nuclear reactor, is it still able to be re-used in another reactor?

If it can be re-used, does it need another special type of reactor to be effective?

Are they doing this and I am just unaware of it?


Thanks!

 

[Astronuc]

Plutonium and uranium are recycled and reprocessed into new fuel. The new fuel containing Pu and U in oxide form is known as MOX (mixed oxide), and usually has 6-7% Pu blended into the U in the form of (Pu,U)O₂. The recycled U fuel is ERU (enriched recycled U) or ERPU (enriched reprocessed U). The French have the biggest program, and the Germans the next biggest, then Belgium, UK, Swiss. Japan has a small program. Russian and China also have programs.

 

[vanesch]

The plutonium that is produced in a nuclear reactor, is it still able to be re-used in another reactor?

If it can be re-used, does it need another special type of reactor to be effective?

Are they doing this and I am just unaware of it?


Thanks!

There are 3 levels of re-use of plutonium. One is, as Astronuc pointed out, in current LWR, by making MOX fuel (a mixture of enriched uranium and plutonium). But actually, MOX fuel in current LWR are a kind of a "bricolage", because current LWR weren't designed for the use of plutonium. Plutonium is in fact a great fuel, in some respects even better than enriched U, but some parameters are different. For instance, in the isotopic mix that comes out of a LWR after reprocessing, there is a relatively high quantity of even-A plutonium which is not fissile in a thermal spectrum, but absorbs a lot of neutrons. On the other hand, the effective nu (number of neutrons per fission event) is higher in odd-A plutonium than in uranium. All this means that the neutron transport properties in plutonium are different than in uranium, and current LWR weren't designed for that. They can accept MOX in limited amounts, but the majority fuel must remain enriched uranium.

The second level of re-use of plutonium is by designing a LWR especially on purpose for MOX fuel. The EPR reactor which is now being build in France and Finland is of that design. Theoretically, it can work on pure MOX fuel. I don't know if they will really use it that way.

However, both uses of plutonium recycling have a serious problem, because they are in a thermal spectrum. Plutonium was produced in a thermal spectrum from uranium, and different isotopes are produced one from another by neutron absorption in plutonium. As such, by continuing irradiation in a thermal spectrum, the A number of the plutonium isotopes rises continuously, until Pu-243 is reached, which decays in Am-243. And that's a nuisance. So you can only use plutonium in a limited way in a thermal spectrum: in the end you will have so many even-number A-plutonium, and so much Am-243, that the material becomes unusable as fuel in a thermal reactor, no matter its design.

The REAL use of plutonium is in a fast reactor. There, it is a superior fuel to uranium (because of its higher neutron yield). The heart of a breeder reactor is necessarily made of plutonium, and in a fast spectrum, even-A plutonium is also fissionable, so there is actually no production of high-A plutonium (as it is used as fuel) ; even Am-243 can "burn" in a fast reactor.