Thermal analysis of the hydrogen release behavior of sodium hydride and kinetic analysis using master plot methods.

Hydrogen is a major nonmetallic impurity in the coolant of sodium-cooled fast reactors (SFRs) during normal operation. A higher hydrogen concentration than the gas–liquid equilibrium has been transiently detected in the gas space of actual SFR plants. The presence of several sodium compounds can increase hydrogen generation; however, a thorough understanding of the thermal behavior of candidate reactions is lacking. Herein, thermal analysis reveals the hydrogen release behavior of sodium hydride. Mass spectrometry indicates hydrogen generation with decreasing sample mass, indicating thermal decomposition. Detailed kinetic analysis based on master plot methods indicates that the hydrogen release reaction occurred through a mechanism involving random nucleation and growth of nuclei. Furthermore, the reaction rate was newly formulated based on a kinetic model function representing the above mechanism and the Arrhenius-type reaction rate constant comprising an activation energy of 119.0 ± 0.8 kJ mol−1 and a frequency factor of 1.8 × 107 s−1. These findings will enable the numerical simulation of the hydrogen release behavior in SFRs. [Display omitted] • Thermal analysis revealed the thermal behavior of sodium hydride as a hydrogen release source in sodium-cooled fast reactors. • Detailed kinetic analysis based on master plots showed the reaction rate and mechanism of the thermal decomposition. • A new formula was created for the reaction rate using an Arrhenius-type reaction rate constant and a kinetic model function. • Comparison of theoretical and experimental master plots confirmed a nucleation–growth-type reaction mechanism. [ABSTRACT FROM AUTHOR]