Revision of the criticality safety handbook in light of the reality of the nuclear fuel cycle in Japan; With a view to transportation and storage of fuel debris

Suyama, Kenya; Ueki, Taro  ; Gunji, Satoshi  ; Watanabe, Tomoaki  ; Araki, Shohei   ; Fukuda, Kodai 

Since the 1990s, the importance of the handbook has changed significantly, as the computational power has improved and continuous energy Monte Carlo codes have become widely used, which enables highly accurate criticality calculations, when necessary, irrespective of the complexity of the system. Because the value of performing a large number of calculations in advance and summarizing the data has decreased, since the second edition was published publicly in 1999, there has been no revision of criticality safety handbooks in Japan for nearly a quarter of a century. In Japan, where the Fukushima Daiichi Nuclear Power Plant accident occurred in 2011, it became necessary to deal with criticality safety issues in the transport and storage of the fuel debris which contains complex constituent elements, and the summary the criticality safety management for such material is an urgent issue. In the area of burnup credit, the transport and storage of fuel assemblies with low achieved burnups due to the consequences of accidents might be the problem. In addition, nuclear data, which is the input for the continuous energy Monte Carlo code, has been improved several times, now JENDL-5 is available from the end of 2021, and its incorporation becomes a need in the field. This report provides an overview of the latest criticality safety research in Japan and the planned revision of the Criticality Safety Handbook, which could be applied to the transport and storage sectors.