Uranium Contamination of Stainless Steel in Nuclear Processing Plants

Abstract

Stainless steel coupons have been exposed to uranium-containing nitric acid solutions, in conditions similar to those found in various uranium handling nuclear facilities across the nuclear fuel cycle. Solid state analysis of the stainless steel samples and solution composition analysis were undertaken to gain a better understanding of the contamination process mechanisms. Stainless steel coupons were immersed in 12 M HNO 3 containing uranium (1 g/L), in the form of uranyl, for periods of up to 255 days. Uranium contamination was observed across all time lengths of exposure. Solution analysis indicated that the levels of contamination reached an equilibrium state after ∼14 days. Investigations using Raman microscopy, synchrotron microfocus X-ray fluorescence and X-ray absorption spectroscopy showed inhomogeneous localization of uranyl species associated with the oxide layer of the stainless steel surface. Over longer time lengths of exposure these contaminant species were predominantly found to locate within intergranular regions of the stainless steel. This finding should be taken into consideration when developing decontamination protocols for corroded stainless steel that has been exposed to uranium, to facilitate metal reuse/recycle and minimize hazardous waste volumes.

Corrosion studies of stainless steel 304 L in nitric acid in the presence of uranyl nitrate: effect of temperature and nitric acid concentration

“…The new data of average corrosion rate obtained here on 304L SS are consistent with previous literature data in similar condition [15,16]. In order to better understand the corrosion mechanism, all coupons were analyzed with SEM-EDX.…”

“…No long term studies in 3.5 and 8 M HNO 3 at 45 and 90 °C have been reported. Recently, Kerry et al [15] studied the corrosion of 304L SS coupons at 50 °C for 155 days with 1.17 mM U with 12 M nitric acid media and reported a rate of about 42 μm y −1 . Unlike previous work [15], uranium is not detected at the surface by EDX spectroscopy.…”

“…Recently, Kerry et al [15] studied the corrosion of 304L SS coupons at 50 °C for 155 days with 1.17 mM U with 12 M nitric acid media and reported a rate of about 42 μm y −1 . Unlike previous work [15], uranium is not detected at the surface by EDX spectroscopy. In the following section, we will discuss more details the effect of temperature, HNO 3 and UN on the corrosion of 304 L stainless steel.…”

“…A recent study [15] has shown that the corrosion of 304 L SS in uranium-containing nitric acid solutions increases with exposure time and has highlighted uranium contamination within intergranular regions of the material, however parameters in this study remains limited (only one temperature has been studied and blank coupons have not been studied). A review [16] on the corrosion behavior of several stainless steels in nitric acid solution indicates that all the corrosion rates reported are below 100 μm y −1 .…”

Understanding the Mechanism of Cs Accumulation on Stainless Steel Suspended in Nuclear High-Level Liquid Waste

“… 28 Similarly, the effect of long-term uranium (U) corrosion on SS 304L was studied under an acidic condition. 29 Uranium was deposited all over the SS surface. The Uranium uptake on SS reached equilibrium after 14 days.…”