Active neutron interrogation (ANI) measurement systems can quantify the fissile masses of special nuclear materials (SNMs) using neutrons and are widely used in nuclear safeguarding fields. However, different hydrogen densities effect the delayed neutron count rate differently, and 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.

This study aims to improve the assay performance of the ANI system in nuclear safeguard measurements by developing a matrix correction method.

Based on the response of the flux monitor, a new matrix correction method was developed based on the conventional correction methods. A WM3210 PAN Shuffler system model was constructed using the Geant4 toolkit, and correction method was explored for common matrix materials. Finally, U₃O₈ materials with different enrichments and distributions were applied to the effectiveness comparison between new correction method and the traditional method.

The results show that for U₃O₈ materials with different enrichments and distribution states, both the traditional correction method and the new correction method can effectively reduce the influence of the matrix material on the measurement of SNM mass. For the case where U₃O₈ material is located at the center of the matrix, the average relative deviation of the ²³⁵U mass obtained by the new correction method is 13.6%, while that of the traditional method is 23.8%. For the case where U₃O₈ material is uniformly dispersed in the matrix, the average relative deviation of ²³⁵U mass obtained by the new correction method is 7.78% whilst that of the traditional method is 20.0%.

Results of this indicate that the new method demonstrates better correction capability than the traditional one.