Criticality safety in nuclear fuel cycle facilities

In Japan where nuclear power generation has reached 20 million kW output, the construction of ther nuclear fuel cycle facilities than nuclear reactors, such as the facilities of uranium enrichment, conversion, fabrication, transport, storage and reprocessing, and plutonium handling facilities for FBRs and future plutonium utilization, has steadily increased. In these facilities, the safety control against criticality is the most important problem, such as the limiting of the types and layout of the equipment handling nuclear fuel, its quantity and degree of enrichment, and the use of neutron absorbers. For expressing the change from the critical condition, the effective multiplication coefficient K(eff) has been used, but there is not the method of its quantitative measurement with practical accuracy for general nuclear fuel facilities. 38 criticality accidents have occurred in the past in the world. In Japan, the experimental study on the criticality of the fuel with indefinite form has been scarcely carried out. In the construction of a large scale reprocessing plant, the design of criticality safety affects its economical efficiency. The present status of the experimental data, design problems, and the computer system for analysis, and the experiment plan on criticality safety are reported. (Kako, I.)