Development of a neutron multiplicity counter system for the nuclear material accounting and safeguards in KAERI

A well-type neutron multiplicity counter (WNMC) system was installed in a hot cell for the purpose of nuclear material control, accounting (NMC and A) and safeguards. The WNMC system determined the nuclear material amount on the basis of the Cm-monitoring method by measuring the neutron multiplicity and the number of coincidence events. The developed system consisted of 20 He-3 tubes with a 2.54 cm diameter and 50 cm length to cover a 25 cm long uniform neutron efficiency region along the tube length direction. As a neutron moderator in order to increase the neutron absorption rate at the He-3 tube, a well type high density polyethylene (HDPE) with a 50 cm diameter was used. The efficiently optimized cylindrical Cd-plate was used in order to satisfy the uniformity along the tube direction. The absolute neutron detection efficiency of the HDPE system was measured about 14.0% and the die-away time was 51.6μs. This system will be used not only for NMC and A but also the process for material quality control, for example, decladding performance of rod-cuts and the homogeneity of a mixing powder, waste and ingot. (author)