TABLE OF CONTENTS A range of segments consisting of advanced and conventional materials for claddings and fuel pellets have been provided for this program. Eight types of segments were fabricated by combining seven types of cladding and three types of fuel pellet. In relation to the claddings, two types of benefits were pursued with the new materials. From the viewpoint of increasing the corrosion resistance, two kinds of Zry-Nb, Zr-Nb alloys were tested, MDA and ZIRLO. Additionally, radial texture controlled claddings have been introduced to investigate improved pellet-cladding interaction (PCI) performance. Along with these new materials, conventional claddings were also used for the fabrication of the segments. The range of claddings therefore includes conventional Zircaloy-4 without radial texture control, and low-tin Zircaloy-4, MDA and ZIRLO with and without radial texture control. In relation to the fuel pellets, those with large grain size are tested to assess the potential benefits of the large grains on the capability of the pellet to retain fission products at high burnup and under operational transients. Large grain size was achieved under usual sintering condition by using UO2 powder which has a larger specific surface area, so-called "active powder", produced through modified ADU conversion process [16]. Conventional pellets were also used for reference. The range of fuel pellets therefore includes the large grain pellet, the conventional one manufactured by MHI and the conventional one from ENUSA.
Main test parameters concerning claddings...
