System development and challenges for delayed gamma-ray nondestructive assay in safeguard verification of nuclear material

Rossi, F. ; Rodriguez, D. ; Seya, Michio; Takahashi, Tone; Koizumi, Mitsuo ; Abbas, K.*; Crochemore, J.-M.*; Pedersen, B.*; Bogucarska, T.*; Varasano, G.*; Schillebeeckx, P.*; Kopecky, S.*; Zerovnik, G.*; Mondelaers, W.*; Bonaldi, C.*

New active-interrogation nondestructive assay techniques are needed for safeguard purpose. They can be used for the quantification of the fissile composition in high radioactivity nuclear material samples. One of the techniques under evaluation by the Japan Atomic Energy Agency together with the European Commission Joint Research Centre is delayed gamma-ray spectroscopy. It utilizes a combination of high rate neutron sources and moderation to thermal energy to induce fission in the fissile nuclides. This will allow enhancing the amount of observable coming from the fission of the fissile compared with the fertile nuclides that are usually more abundant in the sample. Analyzing the peaks ratios of gamma-rays with energy above 3 MeV emitted by the short lived fission products produced in the sample, it is possible to verify the initial composition of the fissile nuclides. We are currently designing and testing several different systems with the goal to design a practical and compact system that can be installed in current reprocessing facilities. In particular, this paper describes the different systems currently tested focusing on the different neutron source and moderator material and geometry as well as different gamma-ray detectors. We will also show the new neutron and gamma-ray detector systems we will implement for future test and development. This work is supported by the subsidy for the "promotion of strengthening nuclear security and the like" from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan.