Corrosion performance of metal materials in reprocessing solution of spent nuclear fuel

Takeda, Seiichiro; not registered; not registered  ; not registered ; Kato, Toshihiro*; not registered; Fujisaku, Kazuhiko*

Corrosion performance of materials used for nuclear fuel reprocessing plant was studied for the extension of their lifetime during in-service period. Research was performed focusing on characteristics of reprocessing solution which is very important corrosion factor on environmental side. In the first stage, fundamental corrosion behavior of several kinds of candidate materials such as 304ULC, 310Nb, Ti, Ti-5Ta and Zr was investigated in pure nitric acid solution. Then corrosion performance of such materials in reprocessing environment was made cleared by means of so-called hot test which is used actual reprocessing solution under radioactive conditions. The results are summarized as follows. (1) With regards to the effects of uranium and plutonium on corrosion, high valence plutonium (Pu(Ⅵ)) accelerated the corrosion of stainless steels in nitric acid, but uranium did not affect on them. It is caused by trans-passive dissolution based on the shift of corrosion potential to the noble position. It is thought that the potential shift is caused by increase of the cathodic current on the stainless steel surface due to the reduction of Pu(Ⅵ) to Pu(IV). (2) In fission product (FP) elements, ruthenium accelerated the corrosion of stainless steel in nitric acid when its concentration was comparatively high. Other FP's did not affect on them. The corrosion potential of stainless steel shifts toward noble region by adding ruthenium in nitric acid where high corrosion rates are exhibited. It is thought that the potential shift is caused by the enhancement of cathodic reactions on metal surface due to co-existence of ruthenium in nitric acid. (3) Ti, Ti-5Ta and Zr showed excellent corrosion resistance in nitric acid with and without Plutonium and ruthenium. Especially, Ti and Ti-5Ta showed the improvement of corrosion resistance by co-existing Plutonium or ruthenium. It was explained by chemical stability of surface oxide film due to plutonium or ruthenium oxidant.