Identification and Differentiation of Actinides Inside Nuclear Waste Packages by Measurement of Delayed Gammas

Abstract-The Alpha-activity resulting from the presence of actinides inside nuclear waste packages must be characterized, in order to select the most appropriate means of storage. Non-destructive active methods, based on the fission process, allow the global mass of actinides to be quantified. However, in most cases, these measurements provide no information on the nature of the isotopes. We are currently developing a method dedicated to the identification of the actinides (
²³⁵
U,
²³⁸
U,
²³⁹
Pu) contained inside nuclear waste packages. This technique is based on the detection of delayed gammas emitted by fission products, the latter being created by irradiation with a neutron or photon beam. The delayed gamma spectrum can be thought of as a "fingerprint" of the irradiated sample. Qualitative and quantitative analysis of the peaks allows the actinides to be identified. In this paper, we firstly explain the theoretical principle of our method. We then present experimental results obtained on sample mixtures for both types of interrogation (
²³⁶
U/
²³⁹
Pu in fission,
²³⁵
U/
²³⁸
U in photofission). Finally, we describe the experiments carried out on different mock-up packages, dedicated to the assessment of the performance and limitations of our technique.