[en] We focus in this report on three issues that are of central importance in the management of radioactive high-level liquid waste (HLLW). We show that the only reducing radical that lasts longer than a few ps in typical HLLW, and is capable of generating hydrogen, is NO₃^2-. We measured the lifetime of this species across the whole pH range (3 ≤ pH ≤ 14) and found it to be shorter than ∼15 μs, before is dissociates to give strongly oxidizing NO₂ radicals. We found that it reacts with many proton donors (H⁺ phosphate, borate, NH₄⁺, amines) in a reaction that is not merely an acid-base equilibrium reaction. Using high-level ab initio calculations we estimate its redox potential and pK_a. We have developed methodologies to study the degradation of organic additives to the HLLW (to CO₂ or carbonate) by NO₂. Relative rates of degradation of several complexants were determined using competition kinetics and ¹³C NMR and proton NMR detection techniques. Direct absorption of the radiation (low-energy electrons as well as photons above the ionization threshold) in NaNO₃ single crystal at the solid/vacuum interface led to production of NO, O, and O- as the major products