Evaluation of graphites for structural components of high-temperature gas-cooled reactors

Three commercial US graphite grades have been evaluated for core-support structures and permanent side-reflector blocks in a high-temperature gas-cooled reactor (HTGR). These grades are: 2020 from Stackpole Carbon Company for core-support posts, PGX from Union Carbide Corporation for core-support blocks, and HLM from Great Lakes Carbon Corporation for permanent side-reflector blocks. Grade 2020 had high strength and relatively low impurity content. Its properties were very uniform in localized volumes, but the mean tensile strength differed by 30% from one end of the billet to the other. Variability of properties in PGX was relatively low, but the impurity content was high. Variability of properties within an HLM log was rather high, and the impurity content was also high. Further studies to qualify grade 2020 will be pursued, whereas a reduction of impurity content is being sought for grades PGX and HLM. (author)