Investigation of potential analytical methods for redox control of the vitrification process. [Moessbauer

Abstract

An investigation was conducted to evaluate several analytical techniques to measure ferrous/ferric ratios in simulated and radioactive nuclear waste glasses for eventual redox control of the vitrification process. Redox control will minimize the melt foaming that occurs under highly oxidizing conditions and the metal precipitation that occurs under highly reducing conditions. The analytical method selected must have a rapid response for production problems with minimal complexity and analyst involvement. The wet-chemistry, Moessbauer spectroscopy, glass color analysis, and ion chromatography techniques were explored, with particular emphasis being placed on the Moessbauer technique. In general, all of these methods can be used for nonradioactive samples. The Moessbauer method can readily analyze glasses containing uranium and thorium. A shielded container was designed and built to analyze fully radioactive glasses with the Moessbauer spectrometer in a hot cell environment. However, analyses conducted with radioactive waste glasses containing /sup 90/Sr and /sup 137/Cs were unsuccessful, presumably due to background radiation problems caused by the samples. The color of glass powder can be used to analyze the ferrous/ferric ratio for low chromium glasses, but this method may not be as precise as the others. Ion chromatography was only tested on nonradioactive glasses, but this technique appears to have the required precision due to its analysis of both Fe/sup +2/ and Fe/sup +3/ and its anticipated adaptability for radioactivity samples. This development would be similar to procedures already in use for shielded inductively coupled plasma emission (ICP) spectrometry. Development of the ion chromatography method is therefore recommended; conventional wet-chemistry is recommended as a backup procedure.