Kinetic Study of Sodium-Water Surface Reaction by Differential Thermal Analysis

Abstract

In a sodium-cooled fast reactor (SFR), if a heat transfer tube in the steam generator (SG) is failed, high pressurized water vapor blows into the liquid sodium and sodium-water reaction (SWR) takes place. SWR may cause damage to the neighboring heat transfer tubes by thermal and chemical effects. Therefore, it is important to clearly understand the SWR for safety assessment of the SG. From recent study, sodium (Na)-sodium hydroxide (NaOH) reaction as secondary surface reaction of the SWR phenomena in a SFR was identified by ab initio (first-principle) method. However, kinetics of this reaction is a still open question. Thus, it is important to obtain quantitative rate constant of sodium monoxide (Na2O) generation by Na-NaOH reaction because Na2O may accelerate the corrosive and erosive effects. Differential thermal analysis (DTA) provides us with the valuable information on the kinetic parameters, including activation energy, pre-exponential factor (frequency factor) and reaction rate constant. In this work, kinetic study of Na-NaOH reaction has been carried out by using DTA technique. Based on the measured reaction temperature, the first-order rate constant of Na2O generation was obtained by the application of the laws of chemical kinetics. From the estimated rate constant, it was found that Na2O generation should be considered during SWR. The results can be the basis for developing a chemical reaction model used in a multi-dimensional sodium-water reaction code, SERAPHIM, being developed by the Japan Atomic Energy Agency (JAEA) toward the safety assessment of the SG in a SFR.