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

摘要

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 (β_(eff)) and the neutron generation time (A), are used effectively for the estimation of experimental parameters, and the accuracy of experiments on prompt neutron decay constant (a) and subcriticality (p_$) in dollar units is attained by the numerical results of β_(eff) and A. Furthermore, the value of β_(eff)/Λ is experimentally deduced with the use of the experimental results of a and p_$, ranging between 250 and -80 pcm. Thus, the experimentally deduced values of β_(eff)/Λ 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 A by introducing an acceptable assumption of β_(eff) at near-critical configurations. From the results of experimental and numerical analyses, the experimental value of β_(eff)/Λ is important for the validation of Λ since kinetics parameters are successfully obtained from the clean cores of near-critical configurations in the thermal neutron spectrum.