On the choice of the matrix for heterogeneous transmutation of americium

In this report, the penalties are described when UO2 made of depleted uranium is used as a matrix for the irradiation of americium. Attention is put to the contributions of the uranium to the fission power in the target, to be produced plutonium mass in the target and to the radiotoxicity as a function of the storage time. For thermal reactors with a moderate neutron flux like present-day light water reactors and for fast reactors, the contributions of the uranium to the fission power and to the plutonium mass remain below 30% of the contributions due to the americium. This seems quite acceptable. Because the contribution of the uranium to the radiotoxicity of the irradiated target is also rather low, this means that UO2 made of depleted uranium can be used as a matrix for the transmutation of americium without large penalties. For thermal high flux reactors, the contributions of the uranium to the fission power and to the plutonium mass increase due tu the higher neutron flux and the lower americium contents of the target. Therefore, the use of UO2 made of depleted uranium for the transmutation of americium is not recommended in these cases. (orig.)