Development of an improved method for calculating the effective delayed neutron fraction of a core using a structure with only a few collapsed energy groups

Fukaya, Yuji   

An improved calculation method for effective delayed neutron fraction of core calculations with a few energy groups has been developed in the present study. To obtain the accurate value, many energy groups is needed for the fast energy region to reflect the difference of fission spectra between prompt and delayed neutron. The calculation cost becomes vast for the effective delayed neutron calculations. The error occurrence mechanism has been investigated, and it is found that the error caused by the fission spectra collapsing without adjoint flux weighting after cell calculations. Moreover, the improved method for the fission spectra collapsing with adjoint flux of point calculation is developed. By the proposed method, the effective delayed neutron fraction can be estimated with accuracy even by the core calculation with a few energy groups. This result will contribute to reduce the calculation cost and/or improve the precision for the effective delayed neutron calculation.