Simultaneous removal of NO_x and RuO₄ from dissolver off gas stream of reprocessing plant

Uranium dioxide, mixed uranium plutonium carbide and mixed uranium plutonium dioxide are important nuclear reactor fuels. During reprocessing of these irradiated fuels, they are dissolved in strong oxidising nitric acid to produce a dissolver solution, which is subjected to a solvent extraction process. In a typical PUREX process, the NO_x gas generated during the dissolution of spent nuclear fuel is one of the poisonous gases, as it poses health hazards at levels above 25 ppm. Additionally, the discharge of NO_x through the stack off gas creates air pollution, formation of smog and acid rain, as well as affecting tropospheric ozone. Apart from NO_x the ruthenium is one of the fission product present in spent nuclear fuel is also oxidized to highly volatile and radiotoxic RuO₄ during dissolution. The gaseous RuO₄ is deposited as black ruthenium dioxide (RuO₂) particles when RuO₄ contact with cooler parts of the SS duct and equipment, causing a serious concern to the reprocessing plant. Therefore, the dissolver off gas is scrubbed via dissolver off gas treatment, before releasing into the environment. In order to have effective removal of NO_x and RuO₄, the caustic solution recirculated in to the scrubber unit by a pump. The RuO₄ gas generated due to the oxidation of ruthenium at anode was absorbed in the gas wash bottle containing acidified urea solution and the ruthenium concentration in urea was analysed by spectrophotometry. The scrubbing efficiency of acidified urea solution with respect to NO_x and RuO₄ were calculated and the results are presented