Behavior of iodine, methyl iodide, cesium oxide, and cesium iodide in steam and argon

An experimental program has been initiated with the overall goal of providing a definitive understanding of fission product behavior under conditions applicable to light water reactor accidents in which the fuel rods reach a maximum temperature in the range 500 to 13000C. In order to test the apparatus and techniques of analysis, a series of ten experiments was performed in which selected fission product-type compounds were exposed to high-temperature steam and argon atmospheres. The species investigated were I2, CH3I, Cs2O, and CsI, mainly in a steam atmosphere over the temperature range 500 to 9500C. Iodine remained stable at 8000C in steam and argon, but CH3I decomposed; decomposition rate constants were calculated. Cesium monoxide reacted rapidly with steam to form CsOH (probably the monohydrate) which, in turn, reacted with the quartz furnace tube. Cesium iodide in steam at 7000C decomposed partially by reaction with quartz. Although most of the CsI and the unreacted CsOH was collected in the thermal gradient tube, a small fraction of both these compounds was deposited in the form of particles in the cascade impactor and on the filters