The chemical reactions of Na-Fe-O2-H2O system and their equilibrium constants (600∼1200 K) were expressed in terms of standard equilibrium O2 pressure P0 and standard potential E0. The results were graphically illustrated on the equilibrium daiagrams of log P(O2)(O2 partial pressure) vs. log(Na2O)(basicity) or E(potential) vs. log(O2−)(basicity). These daiagrams visually and comprehensively show the equilibrium relations in the reactions among molten Na with O2, H2O and Fe with their reaction products and give a useful information for analysis of the leakage incident of sodium from the fast breeder reactor of “Monjyu”.
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.
We developed the quantitative monitoring method for coating condition inside a ballast tank. We proposed the coating condition is evaluated with the surface resistance. We developed the identification method to obtain the whole surface resistance from the differential potential induced by the impressed current from an optional anode inside a tank. We introduced differential potential measurement and inverse analysis to obtain the surface resistance representing the coating condition. The potential measurement and quantitative evaluation were conducted in the actual ship. The verification was performed and there was the good agreement between the proposed method and the preliminary visual inspection.