Development of sample assay system equipped with He Alternative Neutron Detectors (ASAS), 1; Design and fabrication of ASAS detector

Ozu, Akira  ; Tobita, Hiroshi; Kureta, Masatoshi   ; Tanigawa, Masafumi ; Mukai, Yasunobu ; Nakamichi, Hideo; Nakamura, Hironobu ; Kurita, Tsutomu ; Seya, Michio

Against the background of the serious shortage of He gas, the Japan Atomic Energy Agency (JAEA) has newly developed an alternative ZnS ceramic scintillation neutron detector for the safeguards, with the support of the government (MEXT). A demonstrator of plutonium inventory sample assay system (ASAS) has been also developed as an alternative HLNCC (High Level Neutron Coincidence Counter). The results from numerical simulations using Monte-Carlo code MCNPX showed that the fundamental performances of ASAS equipped with the 24 alternative neutron detectors, such as neutron detection efficiency and die-away time, equal to or higher than those of conventional HLNCC could be obtained. Here we present the inner mechanical structure of ASAS, together with the results of the simulating design.