Enhanced wear resistance of CrAl-coated cladding for accident-tolerant fuel

Abstract

For enhancing accident tolerance in current operating LWRs, Zr-based claddings with a protective layer, which have outstanding resistance to high-temperature oxidation, are selected as strong candidates for accident-tolerant fuel claddings. One of the key factors determining the successful application of these coated claddings is their ability to maintain their coating layer during normal operation without significant damage. This study aimed to verify the scratch and fretting wear behaviors of coated Zircaloy-4 claddings deposited with a Cr–10Al binary alloy target (CrAl) by the arc ion plating method. In the scratch tests, the commercial Zircaloy-4 samples showed accumulated scratch grooves with ductile chipping caused by adhesive failure. However, there was no gross spallation, except for well-developed scratch traces caused by plastic deformation, on the entire stroke length of the CrAl-coated Zircaloy-4. The wear resistance of the CrAl-coated Zircaloy-4 against the as-received Zr grid was improved significantly because of its high load support capability owing to the coating layer and the formation of a load-bearing layer by the material transfer when compared with the results of the uncoated Zircaloy-4. Furthermore, when the Zr grid was pre-oxidized, the wear amount of the CrAl-coated Zircaloy-4 became negligible owing to the formation of a glaze layer by the interaction with the surface oxide of the Zr grid. According to the results of the high-temperature steam oxidation tests, the defected region of the CrAl coating layer caused by the scratch and fretting wear showed no further significant damage and still acted as a protective layer for enhancing the accident tolerance of the fuel cladding.