Abstract
In a high temperature gas cooled reactor (HTGR), high gaseous impurity levels could lead to carbon transport problem. The carbon transport process is based on two chemical reactions occurring in turn. One is the reaction of the impurity species water and/or CO2 with graphite in the core, and the other is that of produced CO and H2 to form C deposit at metal surface.Carbon deposition occurred on the inner surface of the pressure vessel of the T2 test section in Helium Engineering Demonstration Loop (HENDEL), where the 50t graphite is installed. From the analysis of the deposition, the C was not graphite but amorphous carbon. Chemical reaction should take place.The levels of H2 and CO in He gas remarkably increased just after increasing the temperature of He gas flowing into the graphite from 700°C to 930°C. The increase of the impurities can be regarded as the result of the reaction of graphite with water absorbed in the atmosphere and outgassing of the products.It has been shown that the effective method to reduce the C deposition is the He gas purification taking account of the impurity concentration ratios, H2/H2O and/or CO/CO2 based on the thermodynamical equilibrium state.
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