Year
2019
Abstract
134Cs, 137Cs, and 154Eu are prominent fission product gamma-ray sources in used nuclear fuel. The activity of these fission products is proportional to the fuel burnup and inversely proportional to cooling time. Previous research has studied the use of the 134Cs/137Cs and 154Eu/137Cs gamma activity ratios to determine burnup and cooling time of commercial spent fuel for international safeguards verification. However, it can be difficult to accurately measure 134Cs and 154Eu due to the intense gamma-ray background from other fission products emitted by the used fuel. In this work, we studied the usage of γ-γ coincidence as a method to enhance the accuracy of the 134Cs and 154Eu activity measurements of used TRIGA reactor fuel of different burnup and cooling time for potential safeguards applications. In the preliminary work, fixed sources of 134Cs, 154Eu, 137Cs, and 60Co were combined to simulate a complex gamma spectrum. Coincident gamma peaks from 134Cs and 154Eu were measured using multiple lanthanum bromide (LaBr3:Ce) gamma-ray detectors and a Xia Pixie-4 gamma coincidence system operating in LIST mode and clearly distinguishable 134Cs and 154Eu coincident peaks were recorded. This paper analyzes and discusses the γ-γ coincidence technique for TRIGA reactor fuel measurements and the limits of their application for international safeguards.