AbstractThe sorption of Sr by graphitic materials used in high‐temperature gas‐cooled reactors was studied by applying high‐temperature mass spectro‐metry with a Knudsen cell and the isopiestic method. Sorption isotherms were determined for matrix graphite with Sr concentrations between 3.88 · 10−5and 8.85 · 10−2mol kg−1. The sorption enthalpies and partial pressures determined for concentrations greater than 1.5 · 10−4mol kg−1showed many properties of Freundlich isotherms. The evaluated vaporization enthalpies of Sr(e.g. ΔvH01660= 447. 8 ± 7.7 kj mol−1for a Sr concentration of 3.42 · 10−4mol kg−1) indicate a strong chemisorption of Sr by graphite. An exceptionally high sorption capacity for Sr has been observed for nong