A COMPARISON OF ACTIVE NEUTRON COINCIDENCE COUNTING USING VARIOUS NEUTRON SOURCES AND ITS APPLICABILITY FOR A FISSILE MATERIAL ACCOUNTING IN PYROPROCESS

摘要

KAERI has modified a previously developed passive neutron coincidence counting system for anactive mode operation by adapting various interrogation sources, a neutron generator, a ~(252)Cfisotope, and an Am-Li source, and has measured its performance with natural uranium oxidepowder up to 27.9g of ~(235)U. The objective of this study is to develop a neutron counter for fissilematerial accounting and to evaluate its applicability to a pyroprocess facility. For that reason, anexperimental set-up based on simulation, measurement tests and an analysis of the results havebeen performed by using uranium samples. The experimental results showed an increment ofneutron coincidence counting as the mass of the uranium samples as well as fair agreement withsimulation results. The result of an active counting using a ~(252)Cf showed a relatively lower errorthan other cases, but still not enough to measure small amount of fissile material in a large naturaluranium sample mostly because of its high energy and inherent high background coincidence rate.It would be, however, applicable to an assay of more than 3 kg of uranium with a natural or higherenrichment level in an error range of 4 - 6 %. The experimental result using a single Am-Li sourceshowed weaker coincidence signals due to its low intensity. Comparisons of sensitivities anderrors are made are discussed while different interrogation sources (including a neutron generator)and different gate widths. More experimental approaches to investigate its applicability forpyroprocess materials and the results are described in detail.