Low Activation Reinforced Concrete Design Methodology (13) Technology to Produce Low Activation Steel Reinforcing Bars

摘要

During the decommissioning phase of a nuclear power plant, a large amount of steel scraps are generated. Such scraps can be recycled if their radioactivity are reduced to a level lower than the clearance level by decreasing the radioactive element content. In order to produce low-activation steel, the current situation of steel bars in apan and the contamination sources of the target elements in iron and steel making processes were discussed and the following points were clarified. 1) Co content in steel bars varied widely from 10 to 130 ppm, and the average value was 66 ppm. A good relation was found to exist between the Co and Ni content therefore, the main source of Co can be considered to be Ni-containing scrap or ferro-alloys. 2) Serpentine was identified to be the major contamination source of Co in BF and BOF process, followed by the silica sand. The ratio of the Co to the Fe content in the iron ore varied from 1.5 to 6.5 ppm, depending on the brand. By selecting raw materials, low-Co-containing hot metal was obtained in laboratory experiments. 3) Steel bars and plates with low Co content were produced in the laboratory by the dilution of commercial steel bar with electrolytic iron and the sufficient high level of strengths were confirmed.