Evaluation of Some Low-Activation Structural Materials for Minimizing Radioactive Waste Production by Future Nuclear Fus
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EVALUATION OF SOME LOW-ACTIVATION STRUCTURAL MATERIALS FOR MINIMIZING RADIOACTIVE WASTE PRODUCTION BY FUTURE NUCLEAR FUSION POWER PLANTS ALDO DONATO
Associazione EURATOM-ENEA sulla Fusione, Centro Ricerche Energia Frascati, C.P. 65 - 00044 Frascati, (Rome) Italy
ABSTRACT Taking into account the neutron activation (Bq/kWht) and the environmental
impact in terms of Ingestion Toxic Potential IT (m3 H20/kWht) of radioactive wastes coming from several low-activation structural material candidates for future nuclear fusion power reactors, the contribution of the material chemical composition elements and impurities to the overall radioactivity and IT has been assessed. The chemical impurities, also at very low concentrations, have been ascertained to give, in many cases, a considerable contribution to the radwastes environmental impact, as in the case of SiC/SiC fiber composites materials or low-activation martensitic steels. The orign of impurities origin has been identified and efforts to use this information in the material production processes for nuclear fusion application are suggested. INTRODUCTION Assessment studies of the environmental impact of radioactive wastes from nuclear fusion have been carried out in the past using one or more of the following criteria: safety, maintenance, waste disposal, recycling [1-9]. More recently, some attempts to compare environmental impact of the radioactive waste of future fusion plants and of present fission plants or of toxic heavy metals from thermal power plants, have been published [10], [ 11]. The results of these studies have shown that future fusion power plants, based on the Starf ire type [12], with the use of low-activation materials as structural materials for the reactor, will have a lower waste environmental impact than present nuclear or thermal power plants. In this paper the contribution of each chemical element present in the composition of future fusion reactor structural materials to the total radioactive waste environmental impact in terms of Bq/kWht and Ingestion Toxic Potential (IT) for the public (IT: m 3 H2 0/kWht) as reported in reference [11], is evaluated. The purpose of this study is to identify the chemical elements which, through the neutron activation mechanism, would contribute the most to the overall radioactivity and to the overall IT. Then, after the examination of the role of each of these chemical elements in the material composition, it would be possible to evaluate which possibility could exist for minimizing the radioactive waste production. RADIOACTIVITY AND IT CALCULATIONS On the grounds of radioactivity and IT calculations of radioactive wastes produced by future fusion power plants of STARFIRE design type reported in ref. [11], the IT and radioactivity for each chemical element of three low-activation materials (LAM) have been calculated up to 106 years decay time. These materials are considered as possible alternatives to the Primary Candidate Alloy (PCA), which is an austenitic titanium modified stainless steel, the structural
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