Behavior of Actinides and Other Difficult to Measure Radionuclides in the Melting of Contaminated Steel

Abstract

Metal waste from nuclear power plants is normally contaminated with beta and gamma emitters mainly due to corrosion product radionuclides. Metal waste originating from reprocessing and fuel fabrication plants is contaminated only with alpha emitters (uranium). So far, only radionuclides that can be measured by gamma spectrometry can be quantified. The behavior of alpha emitters is investigated using an artificially added radionuclide in melt experiments.During its 1984–1988 program on decommissioning of nuclear installations, the Commission of the European Communities concluded a 2-yr research contract with Siemens AG, UB Kraftwerk Union on the behavior of radionuclides that are difficult to measure in the melting of steel.Investigation of the radionuclides 55Fe, 63Ni, and 90Sr began with melt experiments on 55Fe (considered an epsilon emitter) at laboratory scale, which showed that this nuclide is probably as homogeneously distributed in the melt as 60Co; thus, 60Co can be used as an isotopic indicator for 55Fe. In another melt experiment, 241Am was artificially added to metal waste and melted, showing a decontamination factor of ∼100 even with a very small quantity added (4 × 10−7 g 241Am).As of mid-1988, four melt experiments, each with different melt parameters, have been carried out. The last experiment relates to the melting of carbon steel with metallic uranium additions; although this experiment is not yet completely evaluated, problems related to the direct alpha measuring technique may arise from the disturbance of the radiochemical equilibrium of the uranium decay chain in the melt process.