Pool Boiling Behavior and Critical Heat Flux on Zircaloy and SiC Claddings in Deionized Water under Atmospheric Pressure

Abstract

Recently several researches on SiC material as an alternative of the nuclear fuel cladding have been conducted. From a fundamental point of view, Snead et al. did an extensive investigation on SiC properties. Their work revealed non-irradiated and irradiated material properties. In addition to the existing literature data, they even added new data, particularly in the high-temperature irradiation regime. Moreover, Carpenter has studied performance of a SiC fuel cladding in his Ph. D. thesis. With extensive in-core tests at MITR-II, his works showed the effects of cladding design for monolith and triplex types. He concluded that manufacturing techniques of the SiC cladding affected corrosion rates and swelling behavior after irradiation. For more practical nuclear applications, oxidation rates of a SiC cladding was investigated with a comparison assessment of those of a zircaloy-4 cladding. Lee et al. adopted an oxidation process under the conditions of the Loss of Coolant Accidents (LOCA) in LWRs. They found that SiC oxidation rates were greatly lower than those of zircaloy-4. In order to demonstrate the superiority of SiC cladding in terms of thermal performance, in this study pool boiling heat transfer experiments were carried out in a pool of saturated deionized water (DI water) at atmospheric pressure. For a comparison study, zircaloy-4 claddings, which are current fuel claddings in LWRs, were used as a reference case. Not only measuring nucleate boiling heat transfer coefficient (NBHTC) and critical heat flux (CHF) but also observing boiling behavior of both the claddings were conducted. In this study, pool boiling heat transfer experiments with zircaloy and SiC heaters were carried out. Comparison of the CHF and nucleate boiling heat transfer of the zircaloy-4 and SiC cladding were compared. Specifically, sophisticated high-speed photographs of nucleate boiling, the CHF, and film boiling phenomena were captured. · Structural integrity of the SiC heaters was preserved even after experiencing the CHF whereas the zircaloy heaters failed and were fragmented. This demonstrates the superiority of the SiC cladding in terms of the improved safety margin for nuclear applications and resistance to severe accidents during transient conditions