Derivation of scattering kernel for organic moderator and criticality analysis of a system consisted of organic moderator-mixed oxide fuel pin assembly

Critical experiments of mixed oxide fuel pins in organic moderator have not been analyzed with the proper thermal scattering kernel for organic moderator. Usually the scattering kernel of hydrogen atoms in organic moderator are substituted by the scattering kernel of hydrogen atoms in light water. This was caused by the fact that there exist no reliable data concerning thermal scattering cross section of hydrogen atoms in organic moderator. Then, we synthesized a scattering kernel of hydrogen atoms in 32 vol% Tributyl Phosphate (TBP) and 68% n-dodecane so as to reconstract the measured total cross section of the organic moderator. By using the scattering kernel, we analyzed the critical experiments of the organic moderator and mixed-oxide fuel pin system. The critically analyses were performed with the standard MGCL library and MULTI-KENO. The calculated effective multiplication factor with the new scattering kernel showed lower values and better agreement than the existing results which use the substituted scattering kernel of hydrogen atoms in light water. However, even though it was found that the difference of criticality analysis between the two kernels was not too large (∼0.5% in k-eff's), the lattice pitch dependence of k-eff was improved. (author)