Release of Residues from Melting Norm-Contaminated Steel Scrap. A German Approach

摘要

As many raw materials like crude oil, natural gas, mineral sands, phosphor ores and others are contaminated by radionuclides from the Uranium and/or Thorium decay chain (NORM), also plants for processing these materials became contaminated during operation. When plants are shut down, large quantities of pipes, valves, pumps and other components have to be scrapped. As scrap yards and steel mills are equipped by large detector systems to avoid an input of radioactivity into the steel cycle, decontamination is required before recycling. Siempelkamp is operating a melting plant for processing NORM and/or chemically/ toxically contaminated steel scrap. Beside the decontaminated steel as output, residues like slag and filter dust have to be managed within the range of licensed values. Based on the European Safety Standard the European member states have to implement radiation exposure from work activities with NORM in their Radiation Protection Ordinances (RPO). The German government revised the RPO in July 2001. Part 3 describes exposure limits for workers and for the public. Exposures from residues management have to meet 1 mSv/year. Brenk Systemplanung has performed calculations for assessing the radiation exposure from residues of the Siempelkamp melting plant. These calculations have been based on the input of metal from different origins and include all relevant exposure pathways in a number of scenarios. The calculations have been based on the dose criterion of 1 mSv/y as required by the German RPO. The methods and results will be presented.