Evaluation of delayed neutron data for thermal fission of U-235 based on integral experiments at semi-homogeneous experiment

Evaluation of the delayed neutron data for thermal fission of 235U is attempted through an indirect method based on the comparison between measured and calculated integral quantities such as kinetic parameters and reactivity worths of fuel rods and burnable poison rods for the critical assembly Semi-Homogeneous Experiment (SHE). The most probable values for both of the effective delayed neutron fraction βeff and the decay constants λ's of delayed neutron precursors are determined from the condition that the sum of the squared deviations of the ratios of calculated to measued values from unity is minimized for the integral quantities. The most probable value of βeff obtained in the present work is significantly large compared with that obtained with the Keepin's delayed neutron data set, and is closer to the value obtained with the ENDF/B-V data file than that with the ENDF/B-IV. On the other hand, the most probable λ values obtained in the present work are not away from those for thermal fission filed in the Keepin's delayed neutron data set. (author)