Corrosion behavior of stainless steel in nitric acid solutions including neptunium

Motooka, Takafumi; Yamamoto, Masahiro 

In order to investigate a corrosion behavior of stainless steel in the typical nuclear fuel reprocessing plant, corrosion tests using nitric acid solution including neptunium were conducted under atmospheric and reduced pressurized conditions in the laboratory where radioactive substance can be handled. Under reduced pressure condition, corrosion of stainless steel was accelerated in nitric acid solution with neptunium than in pure nitric acid solution. Corrosion was more aggressive in heating condition with boiling than in immersion in boiling solution. Corrosion rate of stainless steel was increased as increasing neptunium concentration. Increase of solution temperature accelerated the corrosion rate of stainless steel in nitric acid with neptunium. It is considered that the corrosion rate was accelerated by the increase of cathodic reaction current on stainless steel surface. The corrosion potential of stainless steel is also nobler in nitric acid solution with neptunium than without that. In nitric acid solution including neptunium, the high redox reaction rate of Np(VI)/Np(V) causes re-oxidation of Np. It is considered that the dominance of Np(VI) in nitric acid solution provides the acceleration of stainless steel in nitric acid solutions including neptunium.