Corrosion modeling for carbon steel under oxygen depleted underground environment

Shibata, Toshio*; Watanabe, Masatoshi; Taniguchi, Naoki; Shimizu, Akihiko*

Zairyo To Kankyo, 62(2), p.70 - 77, 2013/02

https://doi.org/10.3323/jcorr.62.70

In the oxygen depleted underground environment, carbon steel reacts with HO, producing H gas and forming corrosion film on the steel surface. Corrosion rate is controlled by diffusion of reaction species through corrosion film. Diffusion constants of some species working in the corrosion process were obtained from literatures. However, no data were found on the diffusion constant of HO in iron oxides based on an appropriate assumption. Mass transfer model for the corrosion rate was used to simulate the corrosion rate of carbon steel. Liquid phase diffusion model of Fe or HO through pores in the corrosion film and solid phase diffusion model of HO through corrosion film itself were examined by Excel simulation. Change in corrosion current density and corrosion loss with time and pH and temperature dependence of corrosion current density were examined. By comparing the results, it is suggested that the solid phase diffusion of HO in the corrosion film controls the corrosion rate of carbon steel in oxygen depleted environment.

Investigation of the long term corrosion resistance of the overpack (Contract research)

Tachikawa, Hirokazu*; Kawakubo, Fumie*; Shimizu, Akihiko*; Shibata, Toshio*; Sugimoto, Katsuhisa*; Seo, Masahiro*; Tsuru, Toru*; Fujimoto, Shinji*; Inoue, Hiroyuki*

JAEA-Research 2006-058, 80 Pages, 2006/10

JAEA-Research-2006-058.pdf:10.86MB

The Japan Nuclear Cycle Development Institute submitted "Second Progress Report on Research and Development for the Geological Disposal of HLW in Japan" to the Japanese government. This report contains investigations of the corrosion life time of the overpack on the basis of experimental data and past research, assuming the ranging geological environment of Japan. However some subjects, such as the behavior of the overpack under high pH conditions and the behavior of the engineering barrier with change of near-field environmental condition with time for promoting reliability have still been left. To take into account these conditions, expert committee composed of metal corrosion science experts were established in the Nuclear Safety Research Association and past research outcomes and the theory of safety assessment were investigated from the view points of long term stability and corrosion resistance of engineering barrier.

Investigations of and Technical Reviews on the Reliability of Prediction for Migration Behavior of Radionuclides (H.16)

Sano, Eri*; Tachikawa, Hirokazu*; Shimizu, Akihiko*

JNC TJ8420 2004-004, 342 Pages, 2005/02

JNC-TJ8420-2004-004.pdf:15.39MB

The research plan of the radionuclides migration drawn up by Japan Nuclear Fuel Cycle Development Institute and its' research outcome were reviewed comprehensively by an expert committee established in Nuclear Safety Research Association. Also, experimental investigations for the migration behavior of actinide elements and fission products in engineering barrier and natural barrier media, and for solution chemistry of them were carried out and discussed by the committee, in order to enhance the reliability of prediction for migration behavior of radionuclides. The subjects investigated by the expert committee are as follows; (1)Diffusion and electromigration behavior of Plutonium in bentnite under reducing condition (2)Numerical analysis of distribution coefficients of nuclides in compacted bentonite using surface complexization model (3)Radioactive disequilibrium of decay series nuclides in natural water and various materials (4)Research on complexation reactions of f - elements

Modeling of carbon steel corrosion under oxygen depleted environment

Shibata, Toshio*; Watanabe, Masatoshi; Taniguchi, Naoki; Shimizu, Akihiko*

no journal, , 

In Japan, High-level radioactive waste produced by reprocessing spent fuels has been planned to be fixed in a glass solid body which is further enclosed in metal canisters. Carbon steel is the candidate material for the canisters, because the corrosion rate of carbon steel is known to be as low as 10 microm per year at an deep underground site. Corrosion rate data of the candidate steel have been accumulated in the laboratory and fields, and the corrosion rate of steel in this environment has been found to be almost 10 microm per year at the initial stage, which decreases gradually with time. In this study, a rational corrosion model assuming the diffusion of HO molecule through the precipitated corrosion film has been developed under oxygen depleted environment. The model also assumes that the dissolution of precipitated FeO film is controlled by mass transfer process through adjusting diffusion layer in the solution. Digital simulation based on the corrosion model was found well to simulate the observed corrosion rate change with time at various pHs and to predict a low and steady state corrosion rate after long time exposure.