Applying Normalization Methods to Advanced Experimental Fuel Counter Measurements for Fissile Mass Quantification in Unirradiated Fuel

The Advanced Experimental Fuel Counter (AEFC) is a nondestructive assay instrument developed for performing neutron coincidence counting measurements of used research reactor fuel assemblies for fissile mass quantification. The instrument is used to perform active and passive measurements of irradiated fuel assemblies, which are used to calculate net active total (Singles) and correlated (Doubles) neutron count rates. The net active Singles and Doubles rates are then used to estimate the residual fissile mass in a fuel assembly using calibration curves. Previous AEFC deployments have resulted in the development and validation of calibration curves for specific fuel assembly geometries; however, due to the AEFC’s sensitivity to each campaign’s operational conditions, these calibration curves are only directly applicable to AEFC measurements of fuel assemblies with those specific geometries. Due to a lack of well-characterized used fuel assemblies to serve as calibration standards, it would be advantageous to extend the use of previously developed and validated calibration curves to different fuel geometries. A new normalization technique was developed to correct measurements of a generalized irradiated fuel assembly to reflect the operational conditions in which previous AEFC calibration curves were developed. This normalization technique was applied to a series of AEFC measurements performed at Los Alamos National Laboratory on a set of fresh, low enriched fuel assemblies with between 25 and 350 grams of fissile mass. The fissile mass predictions for each fuel assembly were found to be within estimated total (stochastic and systematic) uncertainties when applying the calibration curves to the normalized neutron Doubles rates. Demonstrating the effectiveness of the normalization technique on unirradiated fuel serves as a step towards effective normalization of used fuel measurements. This would extend the deployment capabilities of the AEFC to new facilities without the need for separate campaigns for calibration curve development.