MEASUREMENT OF CRITICAL HEAT FLUX FOR SIC-COATED STAINLESS STEEL PLATE AND α-SIC TUBE WITH SHORT-HEATED LENGTH UNDER ATMOSPHERIC CONDITION

摘要

Hydrogen explosion problem has been one of the important issues regarding the reactor safety, especially after the Fukushima accident in Japan. There have been many studies regarding steam and cladding reaction to mitigate the hydrogen explosion problem. Among many material candidates for the claddings of light water reactor (LWR), SiC has been regarded as one of the alternatives due to its excellent properties such as irradiation stability, low thermal expansion, excellent thermal shock resistance and low reaction rate at high temperatures. Furthermore, SiC has low neutron absorption, which is a necessary property for the materials consisting LWR cladding. We thought that one of possible ways to commercialize the SiC cladding in the near future is coating SiC on Zircaloy cladding. To evaluate the heat transfer performance of the SiC surface and its applicability, both pool and flow boiling experiment were carried out. For the pool boiling experiment, critical heat flux (CHF) of the SiC-coated stainless steel plate has been taken at an atmospheric pressure, and the results were compared with that of the bare stainless steel plate. Two levels of thickness for the coating were prepared to assess the thickness effect. In addition, CHF of a bulk α-SiC tube has been taken under the flow boiling condition at an atmospheric condition, and the result was compared with the bare stainless steel tube. According to the pool boiling experiments, both thicknesses of the coated surface have shown enhanced result compared with the bare stainless steel surface because of its great wettability even though the SiC-coated surface was smooth. Also, thicker specimens resulted in higher CHF values than the thinner ones, showing there was a thickness effect. Inflow boiling experiments, the a-SiC tube with roughness on the inner surface has shown better CHF result compared with the bare stainless steel tube due to the roughness and its ability to retain the wetting where water passes.