Determination of Lambda-Mode Eigenvalue Separation of a Thermal Accelerator-Driven System from Pulsed Neutron Experiment

Abstract

Basic research on the Accelerator-Driven System (ADS) with thermal neutron spectrum has been promoted by the Kyoto University Research Reactor Institute. At the Kyoto University Critical Assembly (KUCA), various experiments on thermal ADS with a pulsed spallation source are planned. In such an ADS, neutron flux distribution may be sensitive to the injection of neutrons, and the high sensitivity results in various spatial effects. In this study, a pulsed neutron experiment with 14MeV neutrons was carried out in a thermal ADS of KUCA, to determine the λ-mode eigenvalue separation, which is a quantitative indication of spatial effects. An original data-processing technique was applied to infer prompt-neutron decay constants of fundamental and higher modes from neutron count decay data, and then the eigenvalue separation around 13%Δk/k was obtained from these decay constants.