SUBCRITICALITY ESTIMATION BY VIRTUAL NEUTRON CAPTURE METHOD

The criticality safety control technique is required for the fuel debris removal from Fukushima Dai-Ichi Nuclear Power Station which experienced a severe accident. subcriticality estimation expected to be done with only limited information about while primary containment vessel internal survey work ongoing. purpose of this study develop method called virtual neutron capture method. neutrons surface represent major portion detector counts. consists two evaluations: evaluation at isotope compositions are known by sampling and region these unknown. For unknown composition region, average arbitrary water content given. surveys relationship count multiplication factor any size ratio before on-site evaluation. verified experiments in Kyoto University Critical Assembly. shows that maximum difference reference 4.5 %dk. As result, can adopted monitoring if includes margin %dk within range 0.70 0.95.