EXPERIENCE DEVELOPING POWER PEAKING PENALTIES FOR FUEL ASSEMBLIES RECONSTITUTED WITH STAINLESS STEEL RODS AT OCONEE NUCLEAR STATION

摘要

Fuel assembly to core baffle interactions are a known phenomenon in the utility and vendor community. Currently at the Oconee Nuclear Station, which is owned and operated by Duke Energy Carolinas, there are two primary fuel mechanical concerns involving fuel assembly to core baffle interaction: spacer grid wear and fuel rod wear. While the mechanism of wear is different between the two issues, both may lead to concerns about the integrity of the fuel if no mitigating actions are taken. Hence, Duke Energy has chosen to perform fuel assembly reconstitution-the insertion of stainless steel rods into fuel assemblies that already have resided in the core for at least one cycle of operation-in a proactive fashion to mitigate the risk of fuel failures associated with these mechanisms of wear. The decision to reconstitute assemblies raises the question of how to address the impact to power peaking and, subsequently, the validity of the safety analyses and maneuvering analysis for a given cycle with potentially 50-60 stainless steel rods present in the core. One way is to create rod peaking penalties by modeling the affected fuel assemblies, including their burnup history, both with and without the insertion of the stainless steel rods. A comparison is made between the predicted rod power peaking in both cases, and judgments may be made about appropriate penalties to be applied in subsequent analyses.