[en] On September 30, 1999, a criticality accident occurred at the uranium processing facility of the JCO Co. Ltd. (hereinafter referred to as ''JCO'') Tokai plant, located in Tokaimura, Ibaraki Prefecture. This was an unprecedented accident in Japan's history of peaceful use of nuclear power, resulting in three workers exposed to severe radiation, two of whom died, and the evacuation and enforced indoor confinement of local residents. Nuclear power suppliers must take personal responsibility for ensuring safety. In this connection, the electric power industry, heavy electric machinery manufacturers, fuel fabricators, and nuclear power research organizations gathered together to establish the Nuclear Safety Network (NSnet) in December 1999, based on the resolve to share and improve the level of the safety culture across the entire nuclear power industry and to assure that such an accident never occurs again. NSnet serves as a link between nuclear power enterprises, research organizations, and other bodies, based on the principles of equality and reciprocity. A variety of activities are pursued, such as diffusing a safety culture, implementing mutual evaluation among members, and exchanging safety-related information. Aiming to share and improve the safety culture throughout the entire nuclear power industry, NSnet thoroughly implements the principle of safety first, while at the same time making efforts to restore trust in nuclear power

[en] LWR fuel reprocessing plants reprocess spent fuels which have been burned to approximately a few tens of GWD/MTU in reactors. Viewing the ''burnup'' process from the standpoint of the criticality safety design of the reprocessing plants, the criticality safety of the equipment treating the fuel is considered to be enhanced or the design requirements for criticality safety is presumed to be reduced, as the reactivity of the nuclear fuel materials is lowered because of the following two reasons; changes in the isotopic composition of the fissile nuclides, and increase of the fission products (neutron poisons). In this paper, 19 nuclides in the fission products (FP) having comparatively large neutron absorbability were selected and the results of criticality evaluations with consideration to their neutron absorption effect at the barrel section of the dissolver were described. As a result, by taking the existence of the FP into account, the effective multiplication factor is lowered considerably. The extent of this reduction is expected to be around 50 % to 100 % of that attributable to changes in the isotopic composition of the fissile nuclides. In addition, it has also been found that, by taking the effect of FP into account in the criticality safety design, the processing capacity of a dissolver can be increased up to 1.1 ∼ 4.4 times (the burnup at 5 ∼ 40 GWD/MTU) in comparison with designs which disregard the existence of FP. (author)