Fig. 4-10 500-kg induction furnace used in the melting tests in JAERI The furnace is equipped with a ring hood to prevent dust and generated gases from dispersing during melting.

Fig. 4-11 An example of the partitioning fraction of radionuclides into metal, slag, and dust Melting has the advantage of lowering radioactivity in recycled metal because of the removal of 137Cs (30-year half-life) by evaporation. This makes recycling of metallic waste advantageous.

Fig. 4-12 Specific radioactivity of 60Co at three cross sections of a sample ingot 60Co is uniformly distributed in the ingot. Generally speaking, it is difficult to accurately measure the radioactivity of metallic wastes having irregular shapes but melting makes it easy because the radionuclides in the ingot are distributed uniformly. This advantage allows even low-level residual radioactivity in waste to be estimated, which facilitates comparison with safety criteria for recycling.

Most wastes from decommissioning of nuclear facilities are extremely low radioactive and are reusable as resources by appropriate sorting and treatment. Recycling of decommissioning wastes is a key issue to be promoted. Recycling of metallic waste is already being conducted in many countries including Germany, the United Kingdom, and Sweden. To obtain data, which are indispensable for establishing criteria for rational recycling and the safe treatment of radioactive metallic waste, basic melting tests of ferrous metal wastes were performed in JAERI using a semi-industrial-scale induction furnace having a capacity of 500 kg of steel per batch. These tests revealed the behavior of typical radionuclides present in the decommissioning waste of an LWR. 85Sr (a substitute for 90Sr) and 137Cs were removed from the metal phase by melting while most 60Co, which has a relatively short half-life, remained in the sample ingot (Fig. 4-11). A precise measurement of the residual radioactivity in the ingot can be easily obtained because of the melt-induced homogenization of radionuclides (Fig. 4-12). Data about cross-contamination caused by the residuals in the furnace refractory and the influence of slag basicity on the behavior of radionuclides during melting, which were not clarified in published data from European countries and the United States, were also obtained in these melting tests.

Reference K. Yamate, et al., Radionuclide Transport Behavior during Melting and Ingot Making of Ferrous Waste, Chuzo Kogaku, 68(8), 644 (1996).

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