A thermodynamic study of the chemical speciation of cesium and boric acid on an oxidized stainless steel surface

The objective of this dissertation is to investigate the effects of cesium hydroxide and boric acid on oxidized stainless steel surfaces at high temperatures and one atmosphere of pressure. This is the first experimental investigation of this chemical system. The experimental investigations were performed using a mass spectrometer and a mass electrobalance. An examination of the surface from the different experiments were conducted using a scanning electron microscope (SEM) to identify the presence of deposited species, and electron spectroscopy for chemical analysis (ESCA) to identify the species deposited on the surface.;A better understanding of the equilibrium thermodynamics, the kinetics of the steam accelerated volatilizations and the release kinetics are gained by these experiments. The release rate is characterized by bulk vaporization/gas-phase mass transfer data. The analysis couples vaporization, deposition and desorption of the compounds formed by cesium hydroxide and boric acid under conditions similar to that expected during certain nuclear reactor accidents.;This study shows that cesium deposits on an oxidized stainless steel surface at temperatures between 1000 to 1200 Kelvin. Cesium also deposits on stainless steel surfaces coated with boric oxide in the same temperature ranges. The mechanism for cesium deposition onto the oxide layer was found to involve the chemical reaction between cesium and chromate. Some revaporization in the cesium hydroxide-boric acid system was observed. It has been found that under the conditions used boric acid will react with cesium hydroxide to form cesium metaborate. A model is proposed for this chemical reaction.