Identification of Actinides Inside Nuclear Waste Packages by Measurement of Fission Delayed Gammas

A characterization of the alpha-activity due to the presence of actinides inside nuclear waste packages is necessary to select the best mode of storage. Non-destructive active methods, based on fission process, allow to quantify the global mass of actinides. However, these measurements give no information on the nature of isotopes in most cases. We are currently developing a method to identify actinides (²³⁵U, ²³⁸U, ²³⁹Pu), based on the detection of delayed gammas emitted by fission products. The delayed gamma spectrum can be regarded as a "fingerprint" of the irradiated sample. Qualitative and quantitative analysis of peaks allow an identification of actinides. The main purpose of this paper is twofold. First, basis of this method of differentiation are described. Then, experimental results obtained in fission and photofission are presented, in particular in the case of mixtures containing several actinides.