Study of shields against D-T neutrons for Prompt Gamma-ray Analysis apparatus in Active-N

Furutaka, Kazuyoshi  ; Toh, Yosuke   

No established method exists to non-destructively measure the amount of highly radioactive nuclear fuel materials such as spent fuels, and it is one of the urgent issues in nuclear material accountancy. Therefore, JAEA has started a research on development of innovative non-destructive analysis (NDA) system for Special Nuclear Materials and Minor Actinides, in cooperation with EC-JRC. The aim of the project is to establish an NDA method which can be applied to highly radioactive nuclear materials and develop a demonstration system, named "Active-N", by utilizing an intense D-T neutron source and by combining the following mutually complemental active-neutron NDA methods: DDA, N RTAs, and PGA (Prompt Gamma-ray Analysis). The PGA measurements play a crucial role in the system, because it can detect/quantify neutron poison elements which disturb DDA measurements, as well as explosives and chemical warfare agents, by utilizing a high-energy resolution Germanium detector. To make an NDA system to be efficient one, an intense neutron generator has to be employed. On the other hand, exposure of a Ge detector to an immense amount of fast neutron makes the detector severely damaged and inoperative. Therefore, in order for the system to be efficient, it is essential to develop effective shield of the PGA system against fast neutrons. In this work, by performing particle transport calculation using Monte Carlo method, we have investigated effective shielding methods for the PGA measurement system in the Active-N system, against fast neutrons from the D-T neutron source. Materials and their configurations which effectively reduce fast-neutron doses and at the same time emit no interfering gamma rays, were examined. Through the calculation, a shield which reduces fast neutron dose sufficiently have been developed. This research was implemented under the subsidiary for nuclear security promotion of MEXT.