Reaction between strontium and steam in the primary circuit of HTR-PM: a theoretical investigation

Abstract

In advanced nuclear energy systems, the chemical states and reactions of fission products are critical to their transport and migration. This study employs thermodynamic and kinetic calculations to investigate the sequential reactions between Sr and H₂O, including the Sr + H₂O → SrO + H₂ (singlet state), Sr + H₂O → SrOH + H (triplet state), and SrO + H₂O → Sr(OH)₂ reactions. These calculations elucidate the Sr–H₂O/SrO–H₂O reaction mechanism in the primary circuit of the high-temperature gas-cooled reactor pebble-bed module (HTR-PM). The maximum potential barrier for the dehydrogenation reaction (Sr + H₂O) was approximately 44.63 kcal mol⁻¹, whereas the SrO + H₂O reaction proceeded spontaneously without an energy barrier. The bonding changes in Sr + H₂O and SrO + H₂O were analyzed using a topological method. Chemical bonding primarily involved covalent interactions, with significant contributions from the s and p orbitals of the Sr atom. Reaction rate constants were determined using collision theory and variational transition state theory. The corresponding concentration dependence over time and temperature was obtained. Gaussian-based kinetic calculations validated the chemical states derived from thermodynamic calculations, providing insights into the behavior of fission products in complex systems.