Nuclear Materials Location Based On Neutron Time-of-flight And Fast Coincidence Counting

Reprocessing, nuclear fuel fabrication, or uranium enrichment require large facilities that contain many glove-boxes, tanks and pipes where uranium and/or plutonium can build up. During the cleaning and dismantling of these facilities, the quantity of fissile materials need to be evaluated for nuclear material accounting and control, criticality safety, radiation safety and waste management. Holdup measurements are usually performed using gamma-ray techniques or neutron measurements with 3-He detectors. During these measurements, many factors can influence the result, such as the geometry of the container, the presence of uncharacterized shields and matrix, the location of the source, its distribution and isotopic composition, etc. Neutron time-of-flight event detection and fast coincidence counting can be used to discriminate neutron from gamma and establish the location of nuclear materials. MCNPX-PoliMi is used to model plutonium in a glove box and a tank. An array of plastic scintillators is simulated around the inspected object and a post-processing macro based on ROOT simulates the response of the acquisition system (energy threshold, energy resolution, time jitter, etc.). The neutron time-of-flight technique is performed to identify fission signatures and source location. Afterwards, plutonium mass could be evaluated.