Transport and Deposition of Metals in Sodium-Stainless Steel Systems, (IV)

Abstract

With the object of gaining information on the behavior of radioactive corrosion products such as 54Mn, 65Zn and 124Sb in relation with oxygen concentration in liquid sodium-stainless steel systems, deposition experiments were undertaken with use made of stainless steel capsules, each containing 20 g of sodium and a trace amount of one of these radioisotopes. Each capsule was set vertically and subjected to a steep temperature gradient, descending toward the bottom, for 700 hr of run to let the sodium oxide diffuse through the liquid sodium and settle on the bottom. The oxygen concentration in the sodium was controlled by varying the bottom temperature. The concentrations of the radioisotope at different radial positions on various cross sections along the capsule axis were determined on sodium samples dissected from the capsule after quick solidification of the sodium by chilling. The values of the activation energy of deposition were determined for each radioisotope from partition coefficients, defined as the ratio of specific radioactivity between that of the stainless steel surfaces and that in the liquid sodium. Manganese deposition involves precipitation in the lower temperature region, and adsorption—associated loosely with oxygen in the sodium—in the higher temperatures. Zinc adsorption was observed on the wall surface only when it had been previously treated with sodium before dissolution of the radioisotope in the sodium. Antimony deposition is attributable to coprecipitation with sodium oxide.