Penertration behavior of cesium in oxide film growing on surface of stainless steel under condition of high oxygen potential.

概要

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The penetration behavior of Cs was studied in the oxide layer growing on SUS-316 stainless steel for a cladding material of fast breeder reactors under the condition of an oxygen potential controlled by a Ni/Ni0 oxygen buffer in the temperature range of 600750°C, using radioactive 134Cs as a tracer. Two different kinds of oxide layers grew on the specimen. Outer Fe-rich and inner Cr-rich oxide layers were formed above and below the original surface of the specimen, respectively. The penetration behavior of Cs in both oxide layers was determined by measuring the residual radioactivity on the surface of the specimen after successive sectioning. The residual radioactivity showed no change with the depth in the outer oxide layer, which means very high permeability of Cs through grain-boundaries or pores in this layer. The residual activity decreases with the depth in the inner oxide layer. Apparent diffusion coefficients were determined from this profile and their magnitude was two or three orders larger than the one of diffusion coefficients of 134Cs in the stainless steel. From this fact, it was suggested that the oxide layer is not protective against the penetration of Cs. In addition, some considerations were given to the mechanism of cladding corrosion.
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