Fretting wear damage resulting from fuel rod vibration is a major concern for EDF. Leaking fuel rods, caused by fretting or not, will cause the contamination of the primary coolant. This contamination can have some safety, radiation protection and financial consequences such as early plant shutdown in order to respect the criterion on fission gas released in the primary coolant, longer outage or specially trained staff to prevent contamination risk when dealing with leaking fuel assemblies. EDF is therefore very sensitive to the prevention of leaking fuel rods resulting from grid to rod fretting (GTRF). Two major phenomena can be responsible for GTRF wear on the rods: important vibration of the fuel assembly structure and excessive vibrations of the fuel rods caused by the flow induced vibration (FIV). As the FIV of the assembly can be detected without too much trouble, this paper will concentrate on the second cause that has been responsible for most of the fretting wear damage leading to leaking fuel rods in EDF PWR plants. The main parameters that have been identified as having the most impact on GRTF are the transverse flow fields and thegrid to rod support conditions. After introducing the key parameters, the methodology applied by EDF to discriminate and qualify new designs proposed by its suppliers in regards to this phenomenon will be detailed. The appearance of fretting wear on the rods being a very random mechanism, the validation is based on an endurance test achieved on a scale 1 fuel assembly mockup, and on operating feedback analysis.
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