Experimental Study and Model Development on the Moisture Effect for Nuclear Graphite Oxidation

A number of experiments were carried out to investigate the effect of moisture - which is always present in environmental air - on the graphite oxidation rate. A porous metal with 10-m pores was used to enhance the humidification at the outlet of the vertical column that is full of water and is designed to increase the moisture on the helium gas when it is passed through the porous media located at the bottom of the water column. The relative humidity (RH) of the mixture was controlled between 0 and 70% by a humidity sensor. The experiment was performed at temperatures ranging from 873 to 1573 K, mole fractions of oxygen from 0.09 to 0.17, and RH from 0 to 70% at the normal condition.

Assuming that the effect of moisture affects only the mass transfer, we derived a theoretical model for mass transfer that included the fast homogeneous CO combustion reaction. The present model shows that the mass transfer rate of humid air is half of the mass transfer rate for dry air. The predictions by the model agree with experimental data within 17%.