Evaluation of initial temperature effect on transient fuel behavior under simulated reactivity-initiated accident conditions

In order to evaluate possible effects of initial temperature on the transient fuel behavior, such as cladding deformation and fission gas release, under reactivity-initiated accident conditions, two comparative pulse-irradiation tests were performed on identical high-burnup PWR fuel rods under different temperature conditions at the Nuclear Safety Research Reactor (NSRR). The test RH-1 was carried out at room temperature of ∼20degC, while the coolant temperature in the test RH-2 was ∼280degC corresponding to the hot zero power temperature of PWR. The fuel rods did not fail in both tests against fuel enthalpy increases of 462 and 378 J/g, respectively. The results of the two tests were generally consistent with data previously obtained in a number of tests at room temperature, when the data were plotted as a function of the peak fuel enthalpy, not of the maximum increase in fuel enthalpy. Computer analysis using the RANNS code confirmed that the cladding residual deformation in the test RH-2 was driven only by the pellet thermal expansion and that the gas-induced deformation did not occur because the cladding temperature did not become high enough to enhance creep deformation even in the film boiling on the cladding surface. (author)