PNNL

Abstract

Reactive nitrogen species (RNS), along with reactive oxygen species (ROS), are significant products from radiolysis in solution. While much research has been focused on biological systems, these species are also important products in the autoradiolysis that occurs in nuclear waste. Here we determine the correlation between solution substituents, particularly nitrite, and radical products in highly alkaline solutions relevant to liquid waste. Because these radicals tend to be very short lived, we employ spin trapping in conjunction with Electron Paramagnetic Resonance (EPR) to detect them and quantify their production. Most spin traps do not function in these conditions (>1 M NaOH), however nitroalkanes such as nitromethane will act as spin traps in their aci form, which is dominate at high pH. In order to restrict the products to those originating from nitrite, we use 280-480 nm UV light to generate radicals, avoiding products from the photolysis of water. Under these circumstances, nitric oxide, nitrite radicals and hydroxyl radicals are detected, and the trends with the concentration of the constituents of the solutions are tracked. These include nitrite, nitrate, hydroxide and carbonate. We find that while the equilibrium shifts with increasing pH from hydroxyl radicals to more slowly reacting oxide radicals, the production of nitrite radicals does not decrease.