Measuring Boron Concentration in a Spent Fuel Pool Using Bare and Cadmium Covered Neutron Detectors

Boron concentration present in spent fuel pools often has a significant impact on the measurements of neutron based detection systems developed by the Next Generation Safeguards Initiative (NGSI). As a result, a method of boron concentration determination is desired. Such a measurement will help in the analysis of many of the detection systems. The approach used to quantify the boron concentration in this paper uses two neutron detectors; one is a bare 3He tube and the other is a cadmium (Cd) wrapped 3He tube. The ratio of the two measured count rates is referred to as a cadmium ratio and it scales with boron content in the water. Since the boron in the water preferentially absorbs thermal neutrons, the bare detector response is perturbed relative to the Cd lined detector because the Cd lined tube is essentially insensitive to thermal neutrons. The cadmium ratio was measured at boron concentrations ranging from 0 to 2400 parts per million, by mass (ppm). In addition the experimental results were benchmarked with Monte Carlo N-Particle eXtended (MCNPX) simulations. Additional simulations were done to determine the effectiveness of using results from existing detector designs from the NGSI effort. This work is supported by the Next Generation Safeguards Initiative, Office of Nuclear Safeguards and Security, National Nuclear Security Administration.