2008 Volume 57 Issue 12 Pages 536-541
In order to investigate a corrosion behavior of stainless steel in the typical nuclear fuel reprocessing plant, corrosion tests using nitric acid solution with neptunium were conducted under atmospheric and the reduced pressure conditions in the laboratory where radioactive substance could be handled. An ultra low carbon type of SUS304ULC stainless steel was used. Obtained results were as follows: Under the reduced pressure condition, corrosion of the stainless steel was accelerated in the nitric acid solution with neptunium than in pure nitric acid solution. Under an atmospheric condition, the corrosion rate of the stainless steel increased with increase of neptunium content. The higher solution temperature enhanced the corrosion rate of the stainless steel in the nitric acid solution with neptunium. Thermodynamic data showed that Np(V) oxidized to Np(VI) by concentrated and elevated nitric acid solution. The corrosion potential of the stainless steel shifted to nobler direction in the nitric acid solution with neptunium. It is estimated that the electrochemical reaction of Np(VI)/Np(V) is reversible and the rate constant of the reaction has great values. And it is considered that the dominance of Np(VI) in nitric acid solution accelerated the corrosion rate of the stainless steel in the solutions with neptunium.