DESIGN OF OFF-GAS CLEANING SYSTEMS FOR HIGH-LEVEL WASTE VITRIFICATION.

High-level wastes are generally nitric acid solutions. Vitrification converts the nitrate salts to oxides, forming nitrogen oxides (NO//x) as a by-product. These NO//x releases can be controlled by nitric acid recovery or by conversion of the NO//x to an acceptable species for release, such as N//2O or N//2. The off-gas system must also be capable of controlling any fission products which may be volatilized in appreciable quantities and may be controlled in the off-gas system by absorption or adsorption. Whichever method is used, the recovered fission products must somehow be converted to a safe disposal form. Proposed off-gas systems are described, and areas requiring research and development are discussed.