Uranium contamination of stainless steel in nuclear processing plants

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 HNO₃ 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.