Introduction program of M5TM cladding in Japan

Experience from irradiation in PWR has confirmed that M5TM possesses all the properties required for upgraded operation including new fuel management approaches and high duty reactor operation. Specifically, the alloy M5TM has demonstrated impressive improvements over Zircaloy-4 for fuel rod cladding and fuel assembly structural components. Moreover, several irradiation campaigns have been worldwide performed in order to confirm the excellent M5TM in-pile behavior in very demanding PWR irradiation conditions (high void fraction, heat flux, temperature, lithium content and Zinc injection). Regarding licensing, the authorization for loading M5TM alloy has been granted by US, UK, South Korean, German, Chinese, South-African, Swedish and Belgian Safety Authorities. Also the French Nuclear Safety Authority has given individually its authorization to load all-M5TM fuel assembly batches in 1300MWe plants and a generic license to load all-M5TM fuel in EDF N4 reactors and M5TM fuel clad in 900MWe reactors for MOX parity fuel management. Licensing is also now underway in Switzerland, Finland, Brazil and Spain. The M5TM alloy has demonstrated its superiority at burn-ups beyond current licensing limits, through operations in PWR at fuel rod burn-ups exceeding 71GWd/tU in the United States and 78GWd/tU in Europe. The Japanese nuclear industry has planned a stepwise approach to increase the burn-up of the fuel. Step-I fuel (48GWd/tU Fuel Assembly maximum burn-up) which was introduced in the late 80s. In the 90s started the licensing of the Step-II fuel (55GWd/tU Fuel Assembly maximum burn-up). Because the extension of the burn-up is important to reduce discharge fuel and cycle cost, the Japanese industry has plans to further extend the burn-up. In such burn-up region, fuel cladding with even better corrosion properties and very low hydrogen pick-up shall be necessary. M5TM alloy, with high anticorrosion/hydriding properties, is suitable for not only the Step-II fuel application, but also to the future burn-up extension in Japan. AREVA NP, Kansai Electric's, MHI and NFI, under this quadripartite scheme, are in the process of discussing an introduction program of M5TM cladding in Japan. In this paper, we will present the introduction program of M5TM cladding in Japan supported by an extensive out-of-pile program performed in-house by MHI/MDC and NFI labs and the ALPS program devoted to RIA and LOCA aspects for the high burn-ups. In addition AREVA NP has provided its own large out-of-pile and in-pile data base on M5TM. (author)