Nuclear fuel of the boiling water reactor

This paper generally reviews the design and the present status of development of BWR fuel. The design specifications and operating conditions of 7x7 and 8x8 fuel assemblies are presented together with the accumulation of irradiation data. The importance of minimizing the probability of fuel failure is emphasized. To this end, many irradiation tests are being performed using material testing reactors. The irradiation data from actual power reactors are also important to prove the reliability of the fuel elements. A hot laboratory specially designed for the post-irradiation inspection of BWR fuel is now under construction in Japan. The recent improvements of BWR fuel have been accomplished in the fields of the local hydrogenating embrittlement of zirconium and pellet-clad mechanical interaction. As for the former, the adoption of a ''getter'' and the addition of desiccation process in fuel fabrication are explained. As for the latter, the adoption of chanferred shorter pellets and the improvement of heat treating condition are presented. Finally, the adoption of the new 8x8 fuel assembly is discussed in connection with lowering linear heat rate. (Aoki, K.)