Physical design of a burnup measurement device based on a D–D neutron source

The nuclear fuel burnup measurement is an important part of the burnup credit, which are closely related to evaluating reactor performance, extending fuel utilization cycles, and achieving fuel breeding effects. In this work, an underwater spent fuel assembly burnup measurement device based on a deuterium–deuterium (D–D) neutron source has been designed. The D–D neutrons which are slowed down by the water, bombard the remaining fissile nuclides in the spent fuel to produce the fission neutron signals. The burnup of the spent fuel is determined by obtaining the signals from “U”-shaped detector array., The burnup data for AFA-3G fuel rods within the range of 5000 to 80,000 MWd/tU were calculated by the ORIGEN-ARP code, and the corresponding nuclear fuel are irradiated by D–D neutrons with the fission behavior and fission neutron signals, which are calculated by the Geant4 code. Based on the calculated results, the response relationship between the neutron-induced fission counts and the burnup of the AFA-3G assembly is established with a strong double exponential relationship, R² = 0.9999, for fuel within the burnup range of 5000–80,000 MWd/tU. Results from the simulation revealed that thermal neutrons constituted 88 % of the detected neutrons, and neutrons originating from assembly fission accounted for over 55 % of the detected signal. The designed burnup measurement device can directly measure the nuclear fuel burnup, which provides a technical solution for burnup credit.