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.