Feasibility study of the photofission technique for characterization of 220-L concrete-lined nuclear waste drums at 7 or 9 MeV energies

International audiencePhotofission is a promising technique for the radiological characterization of nuclear waste packages containing concrete matrices. The goal of this paper is two-fold. First, we assess the performance of the photofission technique and characterize radiologically a 220-L nuclear waste mock-up drum containing a concrete liner using a 9 MeV linear electron accelerator (linac) and uranium or plutonium samples. Delayed neutrons from photofission are detected in an interpulse mode thanks to 3He counters, which are deployed as reference detectors. The minimal masses obtained with the linac operated at 9 MeV and 100 Hz during 10 min are 0.336 grams for plutonium and 0.539 grams for uranium. Second, we build an MCNP6 numerical model of the measurement setup and validate it against the experimental data. Furthermore, using the validated MCNP6 numerical model at 9 MeV we assess the performance of the photofission technique at 7 MeV and with virtual cases representing different matrix materials. Results of this study indicate that a linac operated at 7 MeV could be sufficient for application with concrete, plastic and metallic waste matrices, which fill the entire volume of a 220-L drum