Research and application of plutonium inventory monitoring system for solution systems

In order to monitor the plutonium inventory of the solution system, the “point model” equations originated from the nuclear safeguard for plutonium monitoring were improved to make it applicable to the solution system. The assumptions of the improved point model are: 1) the neutron capture without fission is non-negligible, so the leakage multiplication was substituted by the combination of the net multiplication and the leakage multiplication, 2) the difference in energy spectra between (α, n) neutrons and spontaneous fission neutrons was taken into account, 3) the difference in the detection efficiency between spontaneous fission neutrons, (α, n) neutrons and induced fission neutrons was taken into account. According to the improved “point model” equations, the algorithm for the plutonium inventory of the solution system was proposed, which based on the neutron count rate outside the equipment, combined with the composition ratio of the Pu isotopes. And the plutonium inventory estimation program was developed. For a comprehensive test and validation of the algorithm and the program, a series of experiments were designed and carried out, including the neutron detector performance validation experiments carried out in the laboratory, the plutonium solution sample experiments, and the operational data. The validation results demonstrated a good accuracy of the plutonium inventory estimation algorithm for the solution system. The algorithm has been applied to the reprocessing plants for the real-time online NDA monitoring of plutonium.