b'Wear Performance of a Candidate ATF Cladding Coatingin Grid-to-Rod Fretting Principal Investigator: Jun QuTeam Members/ Collaborators: Brady Reed, Rick Wang and Roger Y. Lu (WEC)A candidate Cr-coatingI n pressurized water reactorssignificantly improve the claddings (PWRs), water flow inducedwear resistance when tested against for ATF cladding hasvibrations cause contact anda commercial Zr alloy grid with or demonstrated superiorrubbing between the fuel rods andwithout pre-oxidization. In addition, wear resistance in grid- the supporting grid, a phenomenonthe Cr-coating also reduced the to-rod fretting. known as Grid-to-Rod-Frettingcounterface wear on the ZIRLO grid (GTRF) [1]. GTRF may producewithout pre-oxidation, but slightly progressive wear damage on theincreased the wear on the pre-oxidized cladding leading to subsequent fuelgrid. The encouraging testing results failure. Such an event is termed aand mechanistic understanding leaker and may cause prematureof the performance improvement and expensive reactor shutdown andprovides scientific insights for further maintenance. Various accident-tolerantdevelopment of ATF claddings to fuel (ATF) [2] concepts are beingmeet Department of Energy (DOEs) developed for enhance the resistanceobjectives of safe, reliable, and of cladding to the high temperatureeconomical operation of the nations steam. One approach is use materialscurrent and next generation reactors.more oxidation resistant than refer- Accomplishments:ence zirconium, most commonly SiCCommercial Zr alloy cladding and grid [2,3] or FeCrAl [3]. Another approachas well as Cr-coated cladding were is to apply a protective surface treat- supplied by Westinghouse Electric ment, e.g. pre-oxidation, or coating,Company (WEC). Microstructure e.g., CrAl [4], Cr [5], and FeCrAl [6],characterization (see Figure 1) revealed to the Zr alloy cladding surface. Whilethat the thickness of the Cr-coating Cr-coatings have shown good prom- is 30-40 m and has a limited ises for ATF claddings, their frettingnumber of voids. The bonding with wear resistance was little known. the substrate appears excellent and Project Description: is absent of gaps or cracks. Based on In this study, fretting wear behavior ofVickers indentation, the Cr-coating a candidate Cr-coating for ATF claddinghas a hardness of 392 HV, about 40% was investigated in a PWR-relevantharder than the commercial Zr alloy environment using a unique bench- cladding. A unique autoclave fretting scale autoclave testing rig at Oak Ridgerig (AFIR, as shown in Figure 2) National Laboratory (ORNL). Testwas recently established at ORNL conditions were designed to mimicto study the wear resistance of the the environment in an industrialcladdings and grids [7]. AFIR allows full-assembly reactor core simulator.grid-to-rod fretting (GTRF) study of Results were compared with that of theactual cladding and grid materials state-of-the-art Zr alloy cladding andin a pressurized water environment. demonstrated that the Cr-coating couldThe AFIR was designed to mimic the 66 2020|AFC ACCOMPLISHMENTS'