Development and Testing of Neutron Detection Systems for Safeguards of Advanced Nuclear Fuels

Abstract

Nuclear safeguards and non-proliferation programs require reliable techniques for detecting and characterizing nuclear materials and for preventing any diversion to non-peaceful purposes such as production of radiation dispersal devices and nuclear weapons. Usually, the verification activities are executed behind a specially designed shielding structure for radiation and information protection. With the small modular reactors that are being considered for construction in the future and their corresponding advanced fuels, the inspection will be more challenging for the present safeguards programs. The new parameters will make it difficult to categorize and estimate the amount of nuclear material. Canadian Nuclear Laboratories is preparing for these future fuels and is developing and testing new technologies to overcome these emerging challenges. Examples include two new neutron detection systems. The first one uses the time-of-flight method where two sets of plastic scintillators are separated by an air gap to make neutron events easily detectable and distinguishable from gamma rays. The second system is based on He-3 detectors with variable high-density polyethylene moderator thicknesses to allow the detection of neutrons in a wide energy range from thermal to fast neutron energies. Experimental tests, in combination with advanced data analysis methods, have shown the effectiveness of both systems for the characterization of unknown nuclear materials, especially those containing plutonium. The paper will provide details of the two neutron systems as well as methods and results of the field tests.