Ab Initio Insight into CsHMoO₄ and H₂MoO₄ Complexes on MoO₃ Surfaces

Solid surfaces play a crucial role in many processes, yet their impact on nuclear safety is not well understood. This study investigates how solid surfaces affect the behavior of radioactive gaseous species, focusing on the interaction of fission product complexes formed under nuclear accident conditions. Specifically, we examine the condensation and decomposition of Cs–Mo complexes, CsHMoO4 and H2MoO4, when interacting with MoO3 deposits in a reactor cooling system, considering two surface terminations: O and Mo. Using density functional theory (DFT), we calculate the Gibbs free energy for these reactions on MoO3 surfaces at temperatures ranging from 300 to 1800 K. CsHMoO4 condenses below 850 K and dissociates between 300 and 650 K on O-MoO3 and 650–1250 K on Mo-MoO3, forming Cs2MoO4 and MoO3, along with steam release. H2MoO4 condenses below 500 K and decomposes between 600 and 800 K, but only on Mo-terminated surfaces. These findings improve the accuracy of nuclear simulations, helping to predict species composition and transport within the reactor cooling system during accidents.