Corrosion Rate of Unalloyed Steels and Cast Irons in Reducing Granitic Groundwaters and Chloride Solutions

Abstract

Measurements of the corrosion rate of unalloyed steel have been made under conditions representative for repositories in the granitic bedrock of Northern Switzerland using two independent methods: (1) Immersion tests in two representative groundwaters, with and without bentonite; (2) Hydrogen evolution measurements in these groundwaters. The immersion tests were carried out at 80°C and 140°C. In both cases the corrosion rate was higher than 50 μm/a as determined at the end of the first observation period of about 500 h. Corrosion rates of under 10 μm/a were estimated after the first 500 h. The corrosion rates were similar in both groundwaters with mineralisations of approx. 3 g/11 and 14 g/11 respectively, and were generally higher at 80°C than at 140°C. The hydrogen evolution measurements allow an hourly determination of the corrosion rate, with a sensitivity expressed as a corrosion rate of better than 0.1 μm/a. The results generally confirm the observation made in the immersion testing; high corrosion rates were observed over the first few days but then decreased to values well below 10 μm/a. The steady state corrosion rates measured were 1.1 μm/a, 6.5 μm/a, and 2.5 μm/a at 25°C, 50°C, and 80°C respectively in the water with the higher mineralisation. The inverse temperature effect on corrosion rate above 50°C is attributed to a change in the nature of the passive film at higher temperatures.

Sorption of selenium(IV) and selenium(VI) onto natural iron oxides: Goethite and hematite

“…In particular, in the case of a HLNWR, selenium might be incorporated onto iron oxy-hydroxides. In this case selenium could interact not only with the iron solid phases of the geological environment but also (and before) with the iron oxy-hydroxides formed as a consequence of the failure or defect of the iron container and its anoxic corrosion [10][11][12]. For these reasons, it is important to study the selenium retention/sorption capacity of the iron solid phases and to evaluate the potential capacity of these solid phases to retard the migration of selenium through the environment.…”

Interaction of uranium with in situ anoxically generated magnetite on steel

“…These two reactions differ in their kinetics, but the direct reaction with water probably is the predominant one considering the concentration of the hydrogen ion in the groundwater [8]. The iron(II) hydroxide is a metastable solid that is transformed into magnetite through the Schikorr reaction: 3Fe(OH) 2 Magnetite is one of the main iron corrosion products under a reducing environment, which is the condition expected to prevail in a deep geological high level radioactive waste repository.…”

Simulation of repository gas migration in a bentonite buffer

“…The corrosion rate is also affected by environmental factors such as pH, contact material, temperature, surface chemistry and the transport of corrosion products. Various experimental studies have been carried out under various environmental conditions (Kursten et al, 1996;Marsh and Taylor, 1988;Marsh et al, 1983;Papillon et al, 2003;Simpson and Valloton, 1986;Simpson et al, 1985;Smart et al, 2006;Taniguchi et al, 2004), with corroborating natural analogue studies (Miller et al, 2000). Gas generation data collated from the literature are shown in Figure 1, which reveals that there is over an order of magnitude difference among the reported values.…”