Concepts in Waste Management: Cerium-Promoted Dissolution of Refractory Actinide Oxides

Abstract

The effective dissolution of refractory plutonium oxide (fired to T ≥ 1000°C) can be carried out by forming ceric nitrate in nitric acid. Preliminary engineering concepts are presented for dissolving such actinide species in the presence of contaminated high-efficiency particulate air (HEPA) filters and incinerator ashes to permit actinide recovery using conventional wet methods. An electrochemical oxidation tank is envisioned with electrodes mounted on the tank lid to facilitate remote operation and maintenance. Contaminated HEPA filters can be treated using an upflow reactor in which ceric nitrate is recirculated between an oxidation tank and a reactor. A membrane separating the electrodes is not required, but special materials of construction are required for all equipment in direct contact with ceric nitrate (e.g., titanium or glass-lined vessels). Since this oxidant is easily reduced to cerous nitrate using oxalic acid, subsequent actinide recovery can be carried out in conventional stainless steel equipment after reduction. The concepts described have been demonstrated on the bench scale.