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The corrosion kinetics of fine grained construction steel (W.Nr. 1.0566), titanium with 0.2% Pd (W.Nr. 3.7568) and tantalum in three oxygen-free chloride salt brines at temperatures between 90°C and 200°C were investigated. Different electrochemical methods were proposed all yielding the same steady state corrosion rates. A procedure was developed and applied to measure the pH of the brines at elevated temperatures. Corrosion of the three materials was uniform. On steel, an inner magnetite or amakinite layer and an outer porous oxide layer containing salt grew according to the paralinear rate law. At the free corrosion potential, depending on temperature and nature of the brine steady state corrosion rates between 10 μA/cm 2 and 100 μA/cm 2 , or between about 0.11 mm/a and 1.2 mm/a, were attained within about a day. The apparent activation enthalpies were small. Hydrogen activities determined from permeation experiments were very low and decreased with temperature. Thus, there is a negligible danger of hydrogen embrittlement. Steady state corrosion rates between 0.1 μA/cm 2 and 10 μA/cm 2 , or between about 0.8 μm/a and 90 μm/a, were observed with TiPd0.2, and between 0.3 μA/cm 2 and 100 μA/cm 2 , or 2 μm/a and 720 μm/a, for tantalum. Activation enthalpies were small or even negative depending on the brine. TiPd0.2 or Ta do not corrode that much slower than steel in order to justify, from the viewpoints of technical properties and economy to prefer them to steel as container material for final disposal of nuclear waste. |
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