Corrosion of type 316 stainless steel with surface heat flux in 1200°F flowing sodium

Abstract

In a sodium-cooled reactor, the surface temperature of the cladding and the bulk liquid temperature increase along the channel as a result of heat generation in the fuel. The difference between the solubility of the corrosion products at the local surface temperature and the corresponding concentration of the corrosion products in the bulk of the sodium provides the driving force for cladding corrosion. The ability to predict this corrosion rate is a prerequisite for proper cladding design and system maintenance. This paper provides a method for estimating the corrosion rate of the cladding when the sodium at the entrance to the fuel channel has an oxygen content of less than 5 ppm and is saturated with respect to the corrosion products. The predictions are based on experimental data of local corrosion rates which were measured along a 3.5-inch sectional cladding sample. The 55°F temperature rise along the surface of the sample was achieved by subjecting the surface to a heat flux of approximately 10 6 Btu/ft 2-hr. From the observed dependence of the local corrosion rate on the velocity (10 and 20 ft/sec) it was concluded that the corrosion rate is controlled by liquid diffusion. In order to obtain agreement of the corrosion rates derived from the theoretical equations with rates which were measured, it was necessary to use the lowest published solubility data of iron in sodium. The diffusion coefficient of iron in sodium was assumed to be that which had been published for the self-diffusion of sodium in liquid sodium. In addition to the total weight loss measurements, the preferential dissolution rates of chromium and cobalt are also presented.