Abstract: The initial step for conventionally reprocessing spent nuclear fuel is to treat the nuclear fuel rods with concentrated nitric acid at elevated temperatures to dissolve out the contents of the fuel rods. The resultant solution contains ruthenium values present in an oxidation state of at least +4 and the presence of such ruthenium values causes intolerably high corrosion of stainless steel equipment which may come in contact with the hot concentrated nitric acid solution. The corrosion of stainless steel from such ruthenium-containing nitric acid solutions may be inhibited by treating the solutions with a reducing agent comprising nitrogen oxide. It is especially convenient to generate the reducing agent in situ by adding a sugar (e.g. sucrose) to the nitric acid solution so as to reduce substantially all of the dissolved ruthenium values having an oxidation state of at least +4 to an oxidation state of less than +4.