Waste transmutation

The nuclear reactions available for nuclear waste processing are of two types:

1. Transmutation, which by neutron capture transforms a radioactive nucleus into a stable one.* This method is suitable for fission products.

* This may involve intermediary steps through short-lived isotopes.

As stable nuclei could be, simultaneously, transformed into radioactive ones, the method may require an initial separation of the isotopes to be transmuted. However 99Tc and 129I do not require such separation.

2. Incineration, which amounts to nuclear fission following neutron capture.* This method is suitable for transuranic elements. It is always associated with energy and neutron production. It is already applied, on an industrial scale, to plutonium.

The plutonium case

From the preceding, plutonium can be considered according to two different viewpoints. In the breeding strategy it is a nuclear fuel. In standard PWR reactors it appears to be a nuclear waste which is apt to be incinerated. Incineration is possible with thermal reactors like PWRs, but complete incineration will be difficult in this case. Indeed, it is associated with the production of transplutonic elements (americium and curium) which are difficult to incinerate in a PWR.

For the thorium-uranium cycle, 233U would have a role similar to plutonium in the uranium-plutonium cycle. However, in this case, the production of transuranic elements is greatly reduced.

Different nuclear waste reprocessing strategies are possible, depending on the availability of existing reprocessing plants, on the experience of incineration in thermal reactors and on the prospect to use fast reactors.

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