2. Principle and issues of separation-transmutation

2.1 Principle

The fundamental principle of ST is to fission minor actinides (see Transmutation box). In a neutron flux, the transmutation of heavy nuclei (U, Pu, minor actinides) depends on competition between fission and capture. The former produces fission products, the latter radionuclides that we want to eliminate. To promote fission, fast neutrons are used, which in turn fission nuclei that have not been fissioned by slow neutrons, such as ²³⁸ U. Moreover, the higher the neutron flux, the more nuclei are destroyed. Ultimately, it is the product of the relative efficiency of nuclear reactions (measured by the ratio of the fission and capture cross sections) and the neutron flux that controls the disappearance of radionuclides. For...