Recycling of radioactively contaminated scrap from the nuclear cycle and from natural sources

摘要

In the beginning of the 80's the Siempelkamp foundry in Krefeld, Germany, developed a process to melt slightly radioactively contaminated scrap originating from maintenance and decommissioning projects of nuclear power plants. The so-called CARLA facility (central facility to recycle slightly radioactive materials) is licensed according to the German Radiation Protection Ordinance since 1989 and is still unique in Germany. Treating metals is limited up to a specific activity of 200 Bq/g with the exemption of 2,000 Bq/g for low beta emitters (H-3, C-14, Fe-55 and Ni-63) and 1,000 Bq/g for scrap contaminated by naturally occurring radioactive materials (NORM). The limit value for the contamination with fissible radionuclides is fixed at 15 g/100 kg scrap. The aim of melting radioactive scrap is to minimize the volume of the scrap and to homogenize remaining radionuclides in the melt or to decontaminate the metal. Depending on the remaining activity, the reuse of the produced ingots can be different: ingots below release limits can be used as input to conventional recycling paths, ingots above these limits are reused for manufacturing casks or shieldings for application in the nuclear cycle. And if ingots are not qualified for recycling they have to be stored for decay before release or will be sent into an atomic depository for final disposal. In 1998, the GERTA facility (large scale melting plant for recycling hazardous wastes) started operation at the Siempelkamp site in Krefeld. Siempelkamp has developed this recycling process in 1996 as a spin-off from the CARLA process especially to treat scrap cross contaminated with NORM and mercury. The GERTA plant is licensed according to the German BImSchG (Federal Law on protection against environmental pollution) and can treat chemically and toxically contaminated scrap (e.g. mercury, asbestos, PCB, furanes, dioxines) as well as NORM contamination up to 500 Bq/g. The final metal product is completely free of all contamination and can be released to the steel cycle without any limitations.