Abstract: The freezing seal chamber is an important part of the sodium valve, which directly relates to whether the sodium valve will leak or not. In this paper, the analysis and design were studied for the freezing seal chamber which was based on the large dimension sodium valve localization project. The freezing seal chamber is a small space, which contains argon, liquid sodium and solid sodium. Using condensation model of FLUENT and combined with basic gas equation for argon, the condensation of the freezing seal chamber was computed and the position of the solid sodium was obtained. Combining the temperature obtained from FLUENT calculation with the correlation of sodium shear force related to temperature, the stress loaded on the sodium solidified plug was analyzed. At last, the dimension of the freezing seal chamber and the height of the sodium solidified plug were obtained, which are 1.5 mm and 197 mm, respectively.