Recycling of Metallic Residues with NORM Contamination by Melting

A lot of branches dealing with raw material generate NORM contaminated scrap from the decommissioning of their facilities. The naturally occurred radioactivity results from the decay of uranium and thorium which is concentrated in scales or sludges on the surface of components and tubes. Scale is formed in gas and oil field equipment due to the precipitation of alkaline earth metal sulphates and carbonates, particularly CaCO3 and Sr/BaSO4 which also contain Uranium and Radium. Depending on the region of the oil and gas field, specific activity is amounting to some hundred Bq/g, often cross-contaminated by mercury and hydrocarbons. Scrapped components from phosphor plants show well detectable activity in scales up to some 10 Bq/g. The welding rod and filament industry generates thoronated tungsten waste with thorium activities between 10-15 Bq/g. Other branches like coal mining, rare earth or non-ferrous metal are to be considered, too. In order to avoid radioactivity input in the steel and non-ferrous metal cycle, scrap yards and steel mills are equipped with gate detectors. Scrap loads with radiation levels above background are rejected at the entrance. Most detections result from NORM contamination in the scrap. For this rejected scrap, Siempelkamp offers the service to decontaminate it in a special melting plant, licensed according to the federal law on protection against environmental pollution (BImSchG). The annual dose exposure to workers does not exceed 1 mSv/a in the plant. In accordance with the European Basic Safety Standard and the German Radiation Protection Ordinance, no licensing nor radiation surveillance or protection is required. Authorized recycling and underground dumping is assured for the waste resulting from the melting process, like slag and dust, in which radioactivity is accumulated. The paper will present experiences and results from melting projects for different industries. (author)