Abstract
The effective delayed neutron fraction βeff for a light water moderated low-enriched UO2 core has been re-evaluated to obtain benchmark data for the validation of calculation codes and nuclear data. Originally, the βeff value was measured by the substitution method. In that method, the βeff value was obtained from measured reactivity change by substituting a Sb-Cd-Pb absorber rod for a 2.6 wt% UO2 rod for all core regions. In the present evaluation, we have employed the latest value for the buckling coefficient of reactivity to re-evaluate the substitution reactivity with high accuracy. In addition, the correction factor, which was ignored in the previous measurement, has been calculated to compensate the difference in the absorption cross sections of fuel and absorber rods. Consequently, the obtained βeff value in the present evaluation was 0.00771±0.00017, and it is more credible than the previous one. The present result is available as benchmark data for the verification of delayed neutron data for light water reactors. For comparison, we have calculated the βeff value using a transport code TWODANT with the JENDL-3.2 nuclear data library. The calculated βeff value overestimated the experiments; the difference slightly exceeded the experimental error.
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