Prediction of oxygen potential in americium thorium oxides phase of a cermet fuel

Osaka, Masahiko; Kurosaki, Ken*; Yamanaka, Shinsuke*

Journal of Nuclear Materials, 362(2-3), p.374 - 382, 2007/05

https://doi.org/10.1016/j.jnucmat.2007.01.083

A new concept of americium-containing target is proposed as a high performance transmutation device for use in fast reactors. The target is designed so as to achieve high irradiation performance. It also meets requirements of reduction of environmental burden and effective use of resources at the same time. Form of the target is a composite of a mixed oxide of (Th, Am)O and metallic molybdenum matrix. Various advantages are expected in the present target as the transmutation device for fast reactor. In particular, overcome of problems derived from high oxygen potential caused by Am oxide is focused on. The oxygen potential, which is one important property especially in views of irradiation behavior, is expected to be maintained as a reasonable level by dissolving it into ThO to form (Th, Am)O solid solution for stabilization of trivalent Am. Structural stability and enhanced thermal properties could also be expected by the formation of (Th, Am)O. Furthermore, the support matrix Mo can give a buffering effect of oxygen potential increase during irradiation, together with enhanced thermal conductivity. Aspects of oxygen potentials are predicted by a chemical thermodynamic model. Fabricability of the target by a conventional powder metallurgy is investigated with surrogate non-radioactive material as a replacement of Am. In addition, as one marked characteristics of the present target, use of recovered Mo from the spent nuclear fuel is envisaged. Neutronic aspects of the target-loaded fast reactor core, which are critical issues since recovered Mo is neutron absorber, together with mass balance of the nuclides such as transmutation rate of Am, are also given.