Delayed neutron measurement in high frequency mode and its application to the determination of fissile content in spent fuel assembly

Abstract

Ahstract-The delayed neutron measurement has been used for the fresh fuel inspection and 235U enrichment measurement of uranium materials for many years. The origin of delayed neutron is the beta decay of fission fragments and the population of fission fragments of right after a fission event decreases as time goes by. In the process of optimization of delayed neutron measurement system using a DT neutron generator to determine the fissile content of spent fuel assembly, we could find out that the utilization of delayed neutron can be maximized by performing the data acquisition of delayed neutron in an earlier time after the fission event. Monte Carlo code simulation results show the delayed neutron count rate obtained in a high frequency mode (100 Hz) is 3.25 times bigger than that acquired in a low frequency mode (0.5 Hz). The influence of delayed neutrons by 238U fission on delayed neutron counts is not negligible. Thus the delayed neutron count rate for 64 cases of spent fuel assembly is corrected by considering the 238U influence.To obtain sufficiently large ratios of signal to background for many cases of spent fuel assembly, 10 10 -lOll nls strength of DT neutron generator is needed.

Characterization of neutron emission during pulse mode of low output electronic neutron generator

“…for delayed neutron counting applications (see e.g. [4]) Measurements with various high voltage and beam current have been performed to show the behaviour at maximum tube parameters (130 kV and 70 µA) and at lower ones. The geometry is shown in the Fig.…”