Tentative set of group constants for C-core of Kyoto University Critical Assembly

A tentative set of group constants is presented for the C-core of the Kyoto University Critical Assembly (KUCA), which is light-water moderated, and which can furnish loadings of three different pitches (2.96, 3.49 and 4.54 mm). The fast group constants were prepared by the familiar computer code ''UGMG-42'', which employs continuous slowing-down model; thermal group constants by ''THERMOS''. Special care has been taken so that the buckling as input data of UGMG is chosen consistently with the leakage in the stage of criticality calculation. With the resulting constants as input, criticality calculation is carried out by a two-dimensional code ''EQUIPOISE-3''. The difference between criticality calculation and experiment proves to be 0.7 -- 2.2%. The effect of diffusion constant on neutron flux is examined by intentionally giving different values of this quantity. In view of the considerable effect, it is concluded that the procedures of producing the thermal diffusion constant for the core has to be further investigated. The exponential attenuation constant of fast neutron flux in the reflector has to be incorporated adequately in future in the fast constant preparation. (author)