Characteristics of Materials Produced by Plasma Treatment of Radioactive Wastes

Abstract

Plasma processes become more and more attractive for the treatment of radioactive low/medium level waste. Plants with throughput rates ranging from 20 kilograms to several hundred kilograms per hour are under construction or under evaluation in different countries. One major installation is under construction at the ZWILAG-site in Wurenlingen (Switzerland). ZWILAG (Zwischenlager Wurenlingen AG) is a company being responsible for treatment and intermediate storage of all radioactive wastes occurring in Switzerland. Thermal destruction (pyrolysis) of organic material and melting of the inorganic residuals and inorganic feed stock can be done simultaneously in a plasma heated vessel. The following output materials are obtained: Metal, glassy slag, off-gas. Depending on feed stock and storage requirements these outputs can have different properties. The distribution of the activity is of particular importance. Isotopes like cobalt-60 (as a metal) partition almost quantitatively to the metal phase. Volatile isotopes like cesium-137 partition to some extent to the off-gas, they can however be retained in the slag to a high extent by employing a two stage process. For some applications the activity in the metal can be kept below the activity tolerance limits making the metal suitable for even non nuclear applications. The most important property of the slag is its leaching behaviour. Mechanical properties can be of importance, too. The paper will present examples from different types of radioactive waste: typical low level mixed waste, ion exchange resins and zeolites, mixtures of concrete and metal, contaminated soil, material contaminated with natural activity and others. Composition of the materials, activity distributions, data on leaching behaviour and some mechanical properties are presented