Effects of Hydrogen/Water Vapor Atmospheres upon Vaporization of UO2-Based Complex Oxides with Sr, Ba, and Cs by Means of High Temperature Mass Spectrometry.

Abstract

For analysis of fission products release and transportation in severe accidents of nuclear reactors, vaporization behaviors of BaUO3, SrUO3, Cs2UO4, and Cs2U4O12 were investigated by using a Knudsen effusion high temperature mass spectrometer. To simulate water vapor and hydrogen environments in severe accident conditions of nuclear reactors, the environmental conditions inside the Knudsen cell were controlled by introducing proper amounts of gases, such as D2(g), D2O(g), O2(g), or their mixtures from outside reservoirs. To maintain dynamic equilibrium being established inside the Knudsen cell, however, the amount of input gas can not be too large. So the experimental result from the mass spectrometry can only apply for a small range of environmental conditions compared to those in a real severe accident of nuclear reactors. A calculation was made by using computer code Chemsage for other possible environmental conditions, such as wet condition with high H2O(g)/H2(g) ratio, reducing condition with low H2O(g)/H2(g) ratio, high temperatures up to 2500 K and high pressures up to 1 MPa. Both the experimental results and the calculation showed that environmental conditions have a great influence on vaporization properties of these compounds.