Hybrid K-Edge Densitometer Monte Carlo Simulations for Safeguarding Pyroprocessing Activities

Since pyroprocessing exists only on a pilot scale, the International Atomic Energy Agency (IAEA) has not yet developed an approach for safeguarding planned facilities. Oak Ridge National Laboratory is home to the Hybrid K-Edge/X-Ray Fluorescence Densitometer (HKED) system, which may be used to support safeguards verification measurements during pyroprocessing activities for nuclear material accountancy. Using a combination of K-edge densitometry and X-ray fluorescence techniques, the HKED quantifies input and product heavy metal actinide elements, such as uranium and plutonium in reprocessing streams. To support this effort, Monte Carlo simulations of the ORNL HKED have been designed for extending the HKED system beyond solutions for aqueous systems with uranium and plutonium ratios of 100:1 to include additional minor actinides from pyroprocessing (neptunium/americium) in spent fuel and where uranium and plutonium ratios approach 1:1. To ensure the simulated spectra are correctly modeled, a comparative analysis has been performed between simulated and experimental results using a new approach. A sensitivity study has been performed on the simulated model to determine impact from a range of factors: e.g. the source directional biasing effects on the spectrum, spectral interference such as absorption and enhancement from matrix effects, and the underlying physics models.