A method for nondestructive assay of nuclear materials in facilities with a pulse neutron generator and a digital technology for discrimination between neutrons and photons

A method for determining the U-235 concentration in fuel assemblies of a high-power channel-type PBMK reactor is described. The measure of U-235 content of an analyzed sample is the number of neutrons from thermal-neutron fission of U-235, normalized to the number of gamma quanta produced in thermal neutron capture by hydrogen nuclei in the scintillator or by B-10 in the glass of a photomultiplier tube. A pulse neutron generator based on DT reaction is the neutron source, and an organic scintillator with the pulse shape discrimination between neutrons and gamma rays with the aid of the digital technology is a detector. The scintillator is also used as a neutron moderator. Simulation of the method shows that the U-235 content of the analyzed sample can be determined for 1 min with an accuracy of 1% or better. The efficiency of the method has been confirmed by experimental investigations on a model of the setup