Development of Low-Alloy Steel for High Level Radioactive Waste Disposal Container

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In order to develop a low-alloy steel container for use in geological disposal of high-level radioactive wastes, a series of 0.12%C steels containing a small amount of alloying elements, which are effective in inhibiting cathodic reactions on Fe_3O_4, were prepared and their corrosion resistance was examined.1. A series of composite oxide films consisting of Fe_3O_4 and MO_x(M: Cr, Mo, Si, Al, Ti, Cu, Ni, Nb) were prepared by ion-beam-sputter deposition and their cathodic polarization characteristics were examined in a simulated solution of water in contact with bentonite (5.72mM-Na_2SO_4+7.99mM-NaHCO)_3 The results showed that the addition of Cr_2O_3, TiO_2, Al_2O_3 and MoO_2 to Fe_3O_4 is effective in suppressing reductive dissolution of Fe_3O_4.2. A series of low-alloy steels containing alloying elements (Cr, Mo, Si, Al, Ti, Cu, Ni, Nb), which are effective in inhibiting reductive dissolution of Fe_3O_4 and in increasing hydrogen overvoltage, were prepared by vacuum induction melting. The corrosion tests were performed in compressed bentonite exposed to the simulated solution of bentonite-contacting water containing 0.5M-NaCl. In the absence of Fe_3O_4film the steels containing 0.5% Cu, Al, Cr or Ti showed good corrosion resistance, while in the presence of Fe_3O_4film those containing Cu, Nb, or Ti exhibited high corrosion resistance. This suggests that Cu is the most promising alloying element for improving corrosion resistance.3. Anodic and cathodic polarization curves of the low-alloy steels developed in the present study were measured in the simulated solution of bentonite-contacting water. The steels having excellent corrosion resistance in the corrosion tests showed a high hydrogen overvoltage and a low reductive dissolution rate of Fe_3O_4.