A large mount of nuclear graphite is adopted in high-temperature gas-cooled reactor (HTGR), with an initial moisture content being about 0.1%. In order to reduce the chemical corrosion reaction between graphite and moisture, it is necessary for graphite material to be dehumidified before operating the reactor. According to the theoretical analysis of certain dehumidifying conditions and pore structure features of graphite, molecular Fick diffusion of vapor through porous media are considered to be the main controlling mechanisms of moisture transfer. The pore structure meets the requirements of seepage which will accelerate the moisture transfer. A simulation of a diffusion model and diffusion-seepage model of moisture transfer was conducted. The simulation result shows the moisture decreases exponentially, and the higher the diffusion coefficient is, the faster the dehumidification is. An accurate diffusion coefficient, which is mainly determined by the diffusion coefficient of gas, open porosity, and tortuosity, is the crucial parameter for humidifying rate in simulation and prediction.

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