The need of interim storage of spent nuclear fuel is increasing in Japan. Concrete cask storage is one of the candidate methods to store spent fuel. The concrete cask storage system uses a cylinder, called a canister, made of stainless steel to confine spent fuel. The canister is subjected to salty environment and should be carefully designed against external stress corrosion cracking (ESCC). Examples of ESCC of stainless steel are described, including time to failure, effect of repetition of dry and wet environments. More research is proposed to ensure the long-term containment function of the canister made of new materials.
The effect of crosslink density of unsaturated polyester resin on the corrosion resistance was investigated. Cured unsaturated polyesters with different crosslink density were immersed in pure water and potassium hydroxide solution. Since the weight of resin increased in proportion to the square root of immersion time in pure water, the diffusion coefficient of water into the polymer was calculated by using the Fick's Law. The greater the crosslink density, the smaller the diffusion coefficient was. On the other hand, corrosion layers with uniform thickness were observed on the specimen surfaces immersed in potassium hydroxide solution. The corrosion depth increased in proportion to the immersion time. The slope between the corrosion depth and immersion time was defined as corrosion rate. The corrosion rate increased with increasing in the crosslink density.
H+ and OH- concentrations and solubilities of Fe2O3 and NiO were calculated in supercritical aqueous electrolyte solutions of HCl, NaCl, NaOH and H2SO4 at 400°C (30 and 60MPa) and concentrations ranging from 10-5 to 0.5mol·kg-1 for the purpose of understanding corrosion behavior at supercritical water condition. At 30MPa, in 0.1mol·kg-1 NaCl solution, OH- concentration was about one order of magnitude higher than that in pure water, namely NaCl solution acted as a base. Calculation made by introducing NaCl into the HCl solutions decreased H+ concentration. At 30MPa, coexistence of 0.1mol·kg-1 NaCl in 0.01mol·kg-1 HCl solution reduced H+ concentration by about 60%. Further, solubilities of metal oxide increased in acid solution and decreased in NaCl and NaOH solutions with increasing pressure. Solubilities also increased with increasing NaCl concentration. At these low dielectric conditions, association of dissolved species consisting of metal oxides in the presence of Na+, Cl- and SO42- were significant in addition to dissociation of acid and base and metal oxide dissolution.
A novel method to protect steel by the application of cements containing with zinc and graphite powders was proposed. The availability of the proposed method was examined by the surface observation of steel and measurement of corrosion potential. Mechanistic studies of the proposed method were also performed on the basis of the anodic polarization curves. The presence of graphite powder decreased the necessary amount of zinc for protection of steel. The polarization curves indicate that the presence of graphite powder greatly increased the anodic current of zinc dissolution.
The effect of potential difference in the solution on the electrochemical system was evaluated with the FEM (Finite Element Method) calculation. We made the theoretical analysis for the effect of Luggin capillary on the potential distribution, and the current distribution on the sample electrode. This calculation evaluated the error in the measurement of electrode potential of the electrochemical system. We proposed the optimal position of Luggin capillary for the electrode potential measurements and mentioned the deviation of the current distribution in the electrode surface by the electrode shapes and by the distance between the electrodes.