AN INVESTIGATION OF CS-PHYLLOSILICATES FOR NUCLEAR WASTE MANANGEMENT

As a nuclear waste cesium has two common radioactive isotopes, 137Cs and 134Cs, both of which pose potential threats in the form of cesium chloride in “dirty bombs”. Na-montmorillonite (SWy-2) readily exchanges with Cs and therefore can be investigated for potential repository phases for radioactive CsCl, making it functionally immobile. Non-radioactive CsCl was exchanged with Na-montmorillonite. Exchange occurs immediately and the Na-montmorillonite changes color and turns from a translucent gel into an opaque paste, indicating a reaction takes place. Scanning Transmission Electron Microscopy (STEM) was used to produce chemical maps of Cs-montmorillonite. The exchanged particles were found to be homogenous although some trace precursor K remained, indicating that a K free montmorillonite would be ideal starting material for Cs sequestration. The Cs-montmorillonite was heated at temperatures ranging from 475 to 675°C. After heating, material was crushed into a powder for investigation by X-ray diffraction. Material was also investigated using Transmission Electron Microscopy (TEM). Both of these techniques indicated that some CsCl remained in samples that were heated for twenty four hours. Initial XRD and TEM data have shown that the most functional heating temperature is 475°C. Runs heated for 7.5 hours at this temperature yield an assemblage of Cs-illite and quartz. The formation of quartz suggests a net loss of Si by the Cs-montmorillonite in the heating process. The Cs-illite + quartz assemblage may be a suitable repository material. The experimental methods used for processing samples simulate a remediation method that could be used in waste deweaponization and storage. We have developed a patent pending technology based on our results.