Matrix-correction method for nuclear-material mass measurement using Shuffler neutron-interrogation system

Active neutron-interrogation (ANI) measurement systems quantify the fissile masses of special nuclear materials (SNMs) using neutrons and are widely used in nuclear safeguarding. However, the hydrogen-containing matrix in the waste drum weakens the signal of delayed neutrons and limits the fissile-mass-measurement precision of the ANI system. [Purpose] The fissile-mass evaluation of SNMs must be independent of the matrix material, and the assay performance of the ANI system in nuclear safeguard measurements must be improved. [Methods] Based on the response of a flux monitor, a new matrix-correction method is developed based on conventional correction methods. [Results]Different hydrogen densities affect the delayed-neutron count rate differently. For U3O8 materials with different enrichments and distributions, the matrix effect may overestimate the observed mass of 235U by up to seven times. For U3O8 materials with different 235U enrichments and distribution states, both the conventional and new correction methods can effectively reduce the effect of the matrix material on SNM measurements. However, compared with the conventional method, the new method achieves better correction results. When the U3O8 material is located at the center of the matrix, the average relative deviation of 235U mass obtained by the new correction method is 13.6%, whereas when the U3O8 material is homogeneously dispersed throughout the matrix, the average relative deviation of 235U mass obtained by the new correction method is 7.78%. [Conclusions] These results confirm the effectiveness and practicality of the proposed correction method.