In-core performance of small sized BWR fuel rod under RIA conditions

A total of 6 experiments with three experiments by triplet rod configurations and three experiments by single rod configuration was carried out in order to understand the in-core performance of small sized BWR fuel rod under reactivity initiated accident (RIA) conditions. Test fuel rods with outer diameter of 11.0 mm and active fuel stack of 135 mm and fully annealed Zr-2 were chosen. Preliminary conclusions of the experiments are; 1. Fuel failure threshold of small sized BWR fuel rod is not less than that of NSRR standard fuel rod. however, failure threshold of former is slightly lower than that of the conventional 8 x 8 BWR fuel rods; 2. No significant differences in the threshold for mechanical energy release exist between the present full rods and conventional 8 x 8 BWR ares; 3. The magnitude of radial permanent strain of Zr liner rods is less than that of non-liner rods; 4. The maximum temperatures of small sized BWR fuel rods are equal to or less than these of NSSR standard fuel rods