PNNL

Abstract

The U.S. Department of Energy Office of Nuclear Energy, Office of Spent Fuel & Waste Disposition is sponsoring a 10 year demonstration of high burnup spent fuel storage in a licensed and instrumented cask. In parallel with this demonstration, 25 high burnup “sibling rods” have been identified that are similar to specific rods within the cask. These rods have been sent to Oak Ridge National Laboratory and Pacific Northwest National Laboratory for characterization by non-destructive examination and destructive examination. The 25 high burnup sibling rods were modeled using the fuel performance code FAST, which is the US Nuclear Regulatory Commission fuel performance code that is maintained by Pacific Northwest National Laboratory. FAST is the next evolution of FRAPCON and FRAPTRAN and contains both steady-state and transient capabilities. The FAST predictions, which were made prior to the receipt of any information from destructive and non-destructive examinations, have been compared to data from each of the sibling rods. In particular, comparisons are made for; oxide thickness, cladding diameter, rod internal pressure, void volume, and gas composition including fission gas release. This paper will describe the modeling that was performed and show comparisons to data. This comparison to data will provide an assessment of the level of accuracy that can be expected when using FAST to model other high burnup fuel rods. Good agreement between model predictions and measured data indicate that FAST is a valuable tool that can be reliably used to predict the thermal-mechanical behavior of high burnup light water reactor fuel under normal operating conditions.