Accident-tolerant fuel (ATF) claddings for LWRs

ATF materials became worldwide a hot research topic after the Fukushima Daiichi accidents. Karlsruhe Institute of Technology (KIT) is involved in various activities on the development and especially high-temperature characterization of ATF cladding materials. Most of these activities are embedded in international collaborations in the framework of IAEA, OECD-NEA, EU as well as cooperation with partners from industry. With the bundle experiment QUENCH-19, the worldwide first large-scale test of ATF cladding under severe accident conditions was conducted in 2018. This test involved FeCrAl cladding produced and supplied by ORNL. Approx. 100 times less hydrogen was released compared to reference test QUENCH-15 with ZIRLO cladding tubes until the end of the reference test scenario, and a coping time of at least 2000 seconds was confirmed. MAX phase coatings for Zr alloys based on the systems Ti/Cr/Zr + Al + C were produced using a unique two-step procedure based on magnetron sputtered elementary nano-layers and subsequent annealing procedure. Most promising results were obtained with Cr2AlC coating. High-temperature oxidation tests in steam atmosphere with these MAX phase coatings as well as a number of most promising ATF cladding types including various other coated Zr alloys, FeCrAl, and SiCf-SiC composites were conducted. Some interesting results with illustrative examples will be presented in this paper.