Investigation on effect of surface properties on droplet impact cooling of cladding surfaces

• Published in: Nuclear engineering and technology 2020, 52(3), , pp.508-519
• Main Authors: Wang, Zefeng, Qu, Wenhai, Xiong, Jinbiao, Zhong, Mingjun, Yang, Yanhua
• Format: Article
• Language: English
• Subjects: Droplet impact; Droplet spreading; Leidenfrost point temperature; Surface oxidation; 원자력공학
• ISSN: 1738-5733; 2234-358X
• DOI: 10.1016/j.net.2019.08.022

During transients or accidents, the reactor core is uncovered, and droplets entrained above the quench front collides with the uncovered fuel rod surface. Droplet impact cooling can reduce the peak cladding temperature. Besides zirconium-based cladding, versatile accidental tolerant fuel (ATF) claddings, including FeCrAl, have been proposed to increase the accident coping time. In order to investigate the effect of surface properties on droplet impact cooling of cladding surfaces, the droplet impact phenomena are photographed on the FeCrAl and zircaloy-4 (Zr-4) surfaces under different conditions. On the oxidized FeCrAl surface, the Leidenfrost phenomenon is not observed even when the surface temperature is as high as 550 °C with We > 30. Comparison of the impact behaviors observed on different materials shows that nucleate and transition boiling is more intensive on surfaces with larger thermal conductivity. The Leidenfrost point temperature (LPT) decreases with the solid thermal effusivity (kρCp). However, the CHF temperature is relatively insensitive to the surface oxidation and Weber number. Droplet spreading diameter is analyzed quantitatively in the film boiling stage. Based on the energy balance a correlation is proposed for droplet maximum spreading factor. A mechanistic model is also developed for the LPT based on homogeneous nucleation theory.