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Yamane, Yuichi; Numata, Yoshiaki*; Tonoike, Kotaro
Proceedings of 11th International Conference on Nuclear Criticality Safety (ICNC 2019) (Internet), 10 Pages, 2019/09
For the criticality safety of the operation treating the fuel debris in Fukushima Daiichi Nuclear Power Plant, the reactivity effect of its geometrical change has been investigated and the developed procedure has been applied to a trial analysis of a postulated scenario for the purpose of its verification.
Tonoike, Kotaro; Yamane, Yuichi
no journal, ,
It is conceivable that a large amount of fuel debris has been produced in the reactors of Fukushima Daiichi Nuclear Power Station (1FNPS) due to the severe core damage and melting. The amount is far beyond minimum critical mass, and essentially subject to criticality control. This presentation will outline the criticality control of fuel debris in the Three Mile Island Nuclear Station, Unit 2 reactor (TMI-2). Then, criticality control problems of fuel debris during the 1FNPS decommissioning will be described contrasting with the TMI-2 case. Finally, technical expectations and research activities of the fuel debris criticality control for the 1FNPS will be presented. It is possible that the fuel debris will be retrieved under nonborated water at the risk of criticality. In this scenario, the risk control, mitigation measures in case of criticality, would be a key factor in safety of the decommissioning.
Yamane, Yuichi; Tonoike, Kotaro
no journal, ,
After the accident of Fukushima Dai-ichi Nuclear Power Station, there is still damaged nuclear fuel in the reactor buildings, which is called fuel debris and contains an amount of fissile materials more than the minimum criticality amount. A new method, which has been developed by Japan Atomic Energy Agency to technically support the Nuclear Regulatory Authority in Japan, NRA, is designed to estimate criticality risk based on a probability distribution of k-eff due to uncertainty of composition and geometry of fuel debris, which method will provide risk information for the criticality safety of fuel debris. A trial analysis by using the procedure defined in the method shows that some events which can initiate criticality can be supposed to happen during maintenance period, and that analysis also indicates countermeasures should be considered as soon as possible in order to reduce criticality risk for public and workers.