Behavior of pre-irradiated fuel under a simulated RIA condition. Results of NSRR test JM-4

摘要

This report presents results from the power burst experiment with pre-irradiated fuel rod, Test JM-4, conducted in the Nuclear Safety Research Reactor (NSRR). The data concerning test method, pre-irradiation, pre-pulse fuel examination, pulse irradiation, transient records and post-pulse fuel examination are described, and interpretations and discussions of the results are presented. Preceding to the pulse irradiation in the NSRR, test fuel rod was irradiated in the Japan Materials Testing Reactor (JMTR) up to a fuel burnup of 21.2 MWd/kgU with average linear heat rate of 27.5 kW/m. The fuel rod was subjected to the pulse irradiation resulting in a deposited energy of 235 (+-) 12 cal/g (center dot) fuel and a peak fuel enthalpy of 177 (+-) 9 cal/g (center dot) fuel under stagnant water cooling condition at atmospheric pressure and ambient temperature. Test fuel rod behavior was assessed from pre- and post-pulse fuel examinations and transient records during the pulse. The Test JM-4 became the first NSRR pre-irradiated fuel experiment resulting in fuel failure. The cladding surface temperature increased to 780degC, and the test resulted in fuel failure with considerable rod diameter increase and rod bending. The test results indicate that number of wall through defects are generated by intensive PCMI (pellet/cladding mechanical interaction) and local hydriding of cladding tube. Significant separation of grain boundaries was observed in extensive area of fuel pellets. (author). (ERA citation 20:021179)