Safety-oriented LWR fuel researches in Japan

The progress to the establishment of the special expert committee on nuclear fuel safety is briefly explained. The feature of this committee is the cooperative researches including experiments. In this paper, the researches on LWR fuel safety in Japan in 20 years are summarized, reviewing the researches in this committee and Japan Atomic Energy Research Institute. When the safety of nuclear fuel is discussed, the state of nuclear reactors is usually classified into normal, abnormal and accident. Concerning the occurrence of leaking fuel in normal state, the baking compacting of fuel pellets, fuel-cladding interaction, and the stress corrosion cracking due to the chemical effect of FP are studied. In abnormal state, power-cooling mismatch and reactivity-initiated accident are the main subjects. In case of accident, the behavior of nuclear fuel in loss of coolant accident has been studied well. The occurrence of leaking fuel cannot be stopped, but the actual number of broken fuel has been very small. The bowing of PWR fuel and its relation to fuel breaking are the peculiar subject of study in Japan. 41 subjects of the researches are listed. The computer codes concerning the behavior of LWR fuel, which were developed in Japan, are explained, and the main ones are FREG-3, ACTIVE-2 and FEMAXI. (Kako, I.)