Development of a Neutron Mu1tiplicity Counter System for the Nuc1ear Material Accounting and Safeguards in KAERl

Abstract

A well-type neutron multiplicity counter(WNMC) system was installed in a hot cell for the purpose of nuclear material control, accounting (NMC&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 50cm 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 NMC8A 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.