System optimization study of hybrid K-edge/XRF densitometer for uranium-plutonium solution measurement

Area of Science:

• Nuclear Chemistry and Materials Science
• Analytical Chemistry
• Radiation Detection and Measurement

Background:

• Accurate quantification of uranium and plutonium is crucial for nuclear safeguards and waste management.
• Existing methods may have limitations in sensitivity or require complex sample preparation.
• A hybrid approach combining K-edge densitometry (KED) and X-ray fluorescence (XRF) offers potential for improved accuracy and detection limits.

Purpose of the Study:

• To develop and optimize a comprehensive hybrid K-edge/XRF densitometer (HKED) device model using MCNP simulations.
• To systematically analyze the physical parameters and material selection for both KED and XRF techniques within the hybrid system.
• To evaluate the performance of the optimized HKED for measuring uranium and plutonium concentrations in solutions.

Main Methods:

• Utilized MCNP (Monte Carlo N-Particle) simulation software to construct a detailed model of the HKED device.
• Conducted systematic simulations to determine optimal parameters for the X-ray tube (voltage, filters), sample vial dimensions, collimator designs, and detector angles for both KED and XRF.
• Performed calibration and validation using simulated uranium and plutonium solutions to assess measurement accuracy and detection limits.

Main Results:

• Identified optimal X-ray tube parameters (160 kV, 1 mm Fe filter) and sample vial dimensions (1.4 cm inner, 2 cm outer diameter).
• Determined optimal KED parameters (1.9 cm Fe filter, 0.08 cm collimator inner diameter) and XRF parameters (0.01 cm Gd filter, 0.3 cm collimator inner diameter, 150° detector angle).
• Achieved a minimum measurement error of 0.4% for uranium concentration, a KED detection limit of ~1 g/L for uranium, and an XRF detection limit of 2.33×10⁻⁴ g/L for plutonium. Linear fitting for plutonium and uranium in mixed solutions showed high coefficients of determination (R² > 0.996).

Conclusions:

• The optimized HKED model provides a robust and accurate method for quantifying uranium and plutonium concentrations.
• The simulation-driven parameter optimization significantly enhances the performance of KED and XRF techniques for nuclear material analysis.
• The HKED device demonstrates excellent linearity and sensitivity for measuring both individual and mixed uranium-plutonium solutions, paving the way for improved nuclear material accountability.