Development of a Predictive Wear Model for Grid-to-Rod Fretting in Light Water Nuclear Reactors
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Copyright 2013 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. The U.S. Dept. of Energy is supporting a multi-party, five-year program called the Consortium for Advanced Simulation of Light Water Reactors (CASL). Its mission is to develop simulations of light water nuclear reactor (LWR) performance that include the capability for enhanced component life prediction. The phenomenon of fretting between clad fuel rods and the metallic grid that holds them in place is a subject within one of CASL's three focus areas. In order to better define the challenge of grid-to-rod fretting (GTRF) and its consequences, a survey of fretting wear and corrosion literature was conducted. Particular attention was paid to the integration of a realistic operating environment with physical processes occurring in the tribological interface. The implications of a non-linear rate of wear are considered. The development of Zr-based alloys in the 1960s, past studies of the corrosion scale-forming mechanisms on those alloys, and the non-steady-state nature of the contact problem between grids and rods are discussed. Attention is paid to the challenges involved in applying results from classical fretting wear studies to the challenging problem of intermittent fretting contact and impacts in flowing hot water environments within a reactor vessel. While daunting in its complexity, a realistic problem definition is essential for the development of predictive wear-life models to support CASL's virtual reactor environment. This paper concludes with a discussion of the "work rate" parameter, and presents a brief summary of GTRF wear modeling approaches that include wear plus oxidation.