Predicted and Observed Scatter in the Fuel Rod Temperature of Replicate Rods During Irradiation

Irradiation data collected from test fuel rods that were identically built and operated may be used to define a range of normal performance for a specific fuel rod design. By comparing the data to computer code calculations, it is possible to define the range of applicability of fuel thermal performance computer codes. Data scatter for the centerline temperature from identical rods in several test assemblies decreases from the first power ascension to the third power ascension. Calculated uncertainty bands for the data (i.e., expected variability for the data assuming dimensional tolerances, material property uncertainties, and power uncertainties) are found to be larger than the data scatter. The FRAPCON-2 temperature calculations agree with temperature data from helium-filled rods; however, the code does not match beginning-of-life temperatures from a xenon-filled rod. However, the code results agreed with data obtained from the xenon-filled rod at higher burnup, thus indicating that the code adequately calculates fuel temperatures for fission gas-filled rods later in life.