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On-line subcriticality measurement using a pulsed spallation neutron source

パルス核破砕中性子源を用いたオンライン未臨界度測定

岩元 大樹; 西原 健司; 八木 貴宏*; Pyeon, C.-H.*

Iwamoto, Hiroki; Nishihara, Kenji; Yagi, Takahiro*; Pyeon, C.-H.*

To investigate the applicability of the pulsed neutron source (PNS) method using a pulsed spallation neutron source (PSNS) for an on-line subcriticality monitoring system for an accelerator-driven system (ADS), a subcriticality experiment is conducted using Kyoto University Criticality Assembly (KUCA) in combination with the fixed-field alternating gradient (FFAG) accelerator. Reactivity values obtained from different traditional techniques, the area-ratio method and the $$alpha$$-fitting method, are discussed with respect to the applicability to on-line subcriticality monitoring. The result shows that the area-ratio method robustly and accurately monitors subcriticality in shallow subcritical states of negative reactivity of up to a few dollars; however with this method, it faces problems with temporal fluctuations, spatial dispersion, and sensitivity to the proton-beam current with increasing depth of subcriticality. As a complement to this method, it is shown that the $$alpha$$-fitting method alleviates such problems in deep subcritical state. Moreover, a proposed fitting technique using the maximum-likelihood estimation method based on the Poisson distribution is robust enough to be applicable for measuring negative reactivity of up to roughly nine dollars.

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パーセンタイル:27.27

分野:Nuclear Science & Technology

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