Corrosion in impure VHTR helium the Framatome-ANP corrosion loop

The coolant gas (VHTR helium) contains impurities of H2, H2O, CH4, CO, N2, CO in the microbar range. The main corrosion effects observed are scale formation, internal oxidation, and carburization or decarburization. The transfer of carbon between atmosphere and the surface is of special importance because changes in carbon content cabn significantly influence the materials properties. Framatome-anp Technical Center has developed a novel apparatus dedicated to the first steps of the corrosion processes (few 100 hours). The objectives are to evaluated the piratical limits in temperature of the candidates alloys and the acceptable range of impurities in the future VHTR. The problems of exactly controlling the very low impurity levels of the test helium are a major difficulty. This apparatus is presented with a short review of the basic corrosion in HTR environment. (authors)