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The measurement of delayed gamma rays following neutron-induced fission is simulated with MCNP 6.1 to investigate the feasibility of fissile material detection in long-lived, medium activity radioactive waste in 870 L drums. The signal from homogeneously distributed fissile material in the drum is several hundred counts in the main delayed gamma peaks of interest. In a peripheral position or in the drum center, the signal is however too small to allow for a reliable measurement. [ABSTRACT FROM AUTHOR]

A gamma and neutron shielding for the HPGe-detector of the MEDINA facility is designed by means of MCNP5 simulations. The performance of the shielding is validated comparing MCNP5 calculations and experimental background reduction factors for easy-to-implement shielding configurations. A good correspondence between simulations and experiment is observed, which comfort the expected background reduction factors of about 4 to 5 predicted by simulation for the neutron and photon currents entering in the detector, respectively, in the case of a complete implementation of the neutron and gamma shielding in MEDINA. [ABSTRACT FROM AUTHOR]

A new analytical facility called MEDINA (Multi Element Determination based on Instrumental Neutron Activation) and based on Prompt- and Delayed-Gamma-Neutron-Activation-Analysis (P&DGNAA) using a 14 MeV neutron generator is developed for the determination of non-radioactive elements and substances in 200-l radioactive waste drums. The qualitative performance of MEDINA is studied by measuring (1) the gamma-ray spectra for the empty chamber, (2) for an empty 200-l steel drum in presence or not of Co and Cs sources and (3) for a 200-l steel drum filled with concrete in order to determine the level of interferences induced by activation products of the facility components and to investigate further optimization steps to improve the measurements sensitivity. The measurement carried out for the empty drum with the radioactive sources show the possibility to characterize radioactive waste packages containing both Co and Cs with activities ranging between 20 and 80 MBq at least. [ABSTRACT FROM AUTHOR]

Abstract: The French Alternative Energies and Atomic Energy Commission (CEA) and National Radioactive Waste Management Agency (ANDRA) are conducting an R&D program to improve the characterization of long-lived and medium activity (LL–MA) radioactive waste packages. In particular, the amount of toxic elements present in radioactive waste packages must be assessed before they can be accepted in repository facilities in order to avoid pollution of underground water reserves. To this aim, the Nuclear Measurement Laboratory of CEA-Cadarache has started to study the performances of Prompt Gamma Neutron Activation Analysis (PGNAA) for elements showing large capture cross sections such as mercury, cadmium, boron, and chromium. This paper reports a comparison between Monte Carlo calculations performed with the MCNPX computer code using the ENDF/B-VII.0 library and experimental gamma rays measured in the REGAIN PGNAA cell with small samples of nickel, lead, cadmium, arsenic, antimony, chromium, magnesium, zinc, boron, and lithium to verify the validity of a numerical model and gamma-ray production data. The measurement of a ∼20kg test sample of concrete containing toxic elements has also been performed, in collaboration with Forschungszentrum Jülich, to validate the model in view of future performance studies for dense and large LL–MA waste packages. [Copyright &y& Elsevier]