Design and Performances of the Scrap Neutron Multiciplicity Counter

Abstract

JRC has developed the SNMC: an advanced neutron multiplicity counter for the verification of inhomogeneous plutonium samples, such as scrap material in MOX fuel fabrication plants. The innovative features of this counter with respect to existing ones rely on two aspects: (i) an optimised design using a large number of Monte Carlo calculations in order to select the most appropriate materials, geometry and detector disposition for maximum efficiency and (ii) the development of a novel electronic based on DSP (digital signal processing) in order to reduce the dead time. The paper will briefly recall the design process, the electronic development, the construction and assembly of the counter. Then the results of the first experimental tests will be reported. We will show the characterisation of the main physical parameters of the counter, the calibration and the verification of a wide variety of plutonium bearing samples available in the PERLA laboratory. This will include pure homogeneous samples (plutonium dioxide powders, metal Pu, MOX powders and pellets) and some tests on heterogeneous samples representative of scrap material.