Experimental Study of Damaged Cr-Coated Fuel Cladding in Post-Accident Conditions

Abstract

To enhance the safety of nuclear power, the focus of researchers all around the world has recently mainly objected on the development of Accident Tolerant Fuels. Especially the Chromium coating of current Zirconium based cladding has been widely suggested and discussed for its immense positive effect on overall cladding properties. Nevertheless, it was observed that during the first stage of the Loss of Coolant Accident, cracks appear in the Cr coating due to its inability to tolerate higher plastic strain. Therefore, experimental methodology used in this article focuses on testing fuel cladding with damaged Cr coating after the high-temperature transient. The impact of cracks on degradation of cladding mechanical properties was observed using optical microscopy, ring compression test, microhardness, and evaluating hydrogen content and weight gain.

Review on chromium coated zirconium alloy accident tolerant fuel cladding

“…The tensile test of dog-bone shape Cr coated Zr alloy samples performed by Jiang et al [86] also indicates that the strength and elongation of the samples are significantly improved by the coating. Červenka et al [139] found that the Cr coated specimens feature a significantly longer time to underdo the ductile-brittle transition. The improvement of the strength of the coated samples is due to the relatively higher hardness of the Cr coating: microhardness measurement results of the as-deposited [44] and the oxidized [53] (normal operation conditions) Cr coated Zr alloy shows that the hardness of Cr coating is higher than that of the Zr substrate.…”

“…Due to the harsh environment in accident condition, i.e., thermal expansion, drastic oxidation, irradiation growth and ballooning, the severe deformation of the cladding tube may cause the coating peeling off from the Zr substrate. Ring tensile and compression tests were done by several research groups [44,47,139] to evaluate the adhesion properties and the strength of the Cr coating. As shown in Fig.…”

“…Usually, this type of cracks occurs in the first stage of LOCA, which is ahead of the high temperature steam oxidation process. In order to investigate the effect of the cracks in the coating induced by ballooning, scratches were created by Červenkaa et al [139] in the coating. Oxidation tests of the scratched Cr coating samples did not show obvious oxidation phenomenon through the coating.…”

Degradation of Cr-coated cladding under the simulated Loss-of-Coolant Accident phenomena

“…Following the events at the Fukushima Daiichi (2011) power plant, substantial effort has been made studying the idea of Accident Tolerant Fuel (ATF), which would significantly enhance nuclear safety. In the past decade, a large variety of ATF concepts has been proposed and tested worldwide [1][2][3][4][5][6][7][8][9]. However, the most manageable and short-term approach to enhance the cladding performance is surface modification by specific technologies and various coatings.…”