The Corrosion Rate and the Hydrogen Absorption Behavior of Titanium under Reducing Condition-III

Suzuki, Hiroyuki*; Taniguchi, Naoki ; Kawakami, Susumu

Titanium is one of the candidate materials for overpacks as a high corrosion resistance metal.At the initial stage of repository,oxidizing condition will be given around the overpack because oxygen will be brought from the ground. The oxygen will be consumed by the reaction with impurities in buffer material or corrosion of overpack, and reducing condition will be achieved around the overpack. With the changing of redox condition, the water reduction becomes to dominate the cathodic reaction accompanying hydrogen generation. Crevice corrosion and hydrogen embrittlement are main causes of the damage of long term integrity of titanium overpack.However, it is not known about the corrosion resistance and hydrogen absorption behavior of titanium under reduction condition. In this study, the completely sealed ampoule test and the immersion test of titanium in aqueous solution and bentonite was carried out. In order to obtain reliable data about the hydrogen generation rate and the ratio of hydrogen absorption in titanium.From the result of 3 years immersion tests, corrosion rate of titanium were estimated to be in the order of 10- 10micro m / y in the aqueous solution, and 10- 10micro m / y in bentonaite.This value is almost the same as the last report.Almost all the hydrogen generated by corrosion was absorbed in titanium in the immersion tests in completely sealed ampoule.In the examination that changed each parameter, it was suggested that the amount of the hydrogen absorption become 2 - 3 times in 1M HCO and pH13.