Lumped group constants of FP nuclides for fast reactor shielding calculation Based on JENDL-3.2

not registered; not registered ; Aoyama, Takafumi 

Fission Products (FPs) were not considered in conventional fast reactor shielding analyses that were predominantly developed in clean core experiments like the JASPER program. However, in power reactors with high burn-up, the accumulation of FP affects the neutron balance so it cannot be neglected in the neutron flux calculation. In this study, the lumped group constants of FP nuclides were computed based on the JENDL-3.2 nuclear data library and these were compiled to the JSD-J2 set. Using the constants, the effect of the FP nuclides on shielding calculation was evaluated in the JOYO experimental fast reactor. Generation and depletion for nearly 880 FP nuclides can be computed with the ORIGEN2 burn-up calculation. The calculation uses the specification and material contents of the JOYO Mk-II driver as an example of fast reactor MOX fuel. About 99.8% of the total FP neutron absorption comes from 165 major nuclides. The cross section data for these nuclides are stored in the JENDL-3.2 library. The contributions of other FP nuclides were found to be negligible so the calculation used only these 165 FP nuclides. The lumped group constants for the FP nuclides were generated as follows. The 100 group infinite dilution cross section of each individua1 FP nuclide was computed with the NJOY-94 code. The energy group structure is the same as the JSD-J2 set and the scattering anisotropy is considered up to P3 components of Legendre expansion. Atomic number densities of FP nuclides generated from U, U, Pu and Pu were independently computed by ORIGEN2 as a function of fuel burn-up. The lumped FP constants were then obtained by averaging the infinite dilution cross sections with the atomic number densities based on the assumption that one fission produces one lumped FP. To verify the calculated lumped FP constants, the absorption microscopic cross section data were compared with the JFS-3-J3.2 group constants used for the fast reactor ...