Thermal validation of a multi-dimensional analysis Code BISON for MOX; Okami

Ozawa, Takayuki   ; Hirooka, Shun ; Kamei, Miho; Oki, Takumi; Novascone, S.*; Medvedev, P.*

It is well known that the most typical behavior of MOX fuels irradiated in a fast reactor (FR) would be radial pore migration along the temperature gradient causing fuel restructuring with radial density distribution and finally central void formation. In order to analyze the fuel restructuring behavior, MOX fuel properties and a pore migration model that depends on fuel composition were applied in a multi-dimensional analysis code BISON with specialized MOX features, called Okami, which was developed in cooperation with INL. Since the fuel restructuring takes place at the early stage of irradiation and fuel temperature strongly affects the pore migration behavior, the fuel temperature calculation in Okami was validated by using in-pile fuel center temperature obtained in the INstrumented Test Assembly (INTA) tests, INTA-1 and INTA-2, and power-to-melt (PTM) test, B5D-2, in Joyo. The fuel restructuring behavior calculation in Okami was validated by using Am-MOX irradiation test, B14, in Joyo, in which O/M dependence on central void formation at the early stage of irradiation could be observed. As a result of thermal validation for fuel temperature and fuel restructuring calculations, Okami could precisely represent the MOX fuel behavior at the early stage of irradiation in FR.