Neutron Generation Time in Highly-Enriched Uranium Core at Kyoto University Critical Assembly

At the Kyoto University Critical Assembly experiments on kinetics parameters are carried out at near-critical configurations, supercritical and subcritical states, in the thermal neutron spectrum made with a highly enriched uranium fuel. The main calculated kinetics parameters, the effective delayed neutron fraction (beta(eff)) and the neutron generation time (& x245;), are used effectively for the estimation of experimental parameters, and the accuracy of experiments on prompt neutron decay constant (alpha) and subcriticality (rho($)) in dollar units is attained by the numerical results of beta(eff)and & x245;. Furthermore, the value of beta(eff)/& x245; is experimentally deduced with the use of the experimental results of alpha and rho($), ranging between 250 and -80 pcm. Thus, the experimentally deduced values of beta(eff)/& x245; that reveal good accuracy through a comparison with those by the MCNP6.1 calculations with JENDL-4.0 are then taken as an index of & x245; by introducing an acceptable assumption of beta(eff)at near-critical configurations. From the results of experimental and numerical analyses, the experimental value of beta(eff)/& x245; is important for the validation of & x245; since kinetics parameters are successfully obtained from the clean cores of near-critical configurations in the thermal neutron spectrum.