INVESTIGATION OF PASSIVE GAMMA SPECTROSCOPY TO VERIFY SPENT NUCLEAR FUEL CONTENT*

Measurement of passive gamma rays emitted by the decay of radioactive isotopes is a widely used and fundamental technique to verify and determine characteristics of nuclear materials. Several initiatives are currently under way to investigate the use of advanced nondestructive assay methods for application to independently measure the fissile material and plutonium content in spent nuclear fuel. Although no single technique is capable of accurately measuring the actinide inventory, the integration of multiple measures has the potential to dramatically improve nondestructive analysis capability. These methods are likely to involve the use of high-resolution gamma detectors with the resolving power necessary for isotopic identification. Recent high-resolution gamma-ray spectroscopy measurements of spent nuclear fuel rod segments performed at Oak Ridge National Laboratory provided an important opportunity to analyze and identify the dominant and minor gamma-ray signatures that can be acquired using conventional HPGe detectors. The spent fuel source and detector spectra were simulated to identify potential low-intensity gamma signatures in the fuel that could be observed with modest improvements in detector capability. The measurements represent important experimental benchmarks for code and detector model simulations that will be needed to better determine advance detector design requirements for spent fuel measurements.