TRANSPASSIVE ELECTRODISSOLUTION OF DEPLETED URANIUM IN ALKALINE ELECTROLYTES by Kirk

To aid in removal of oralloy from the nuclear weapons stockpile, scientists at the Los Alamos National Laboratory Plutonium Facility are decontaminating oralloy parts by electrodissolution in neutral to alkaline electrolytes composed of sodium nitrate and sodium sulfate. To improve the process, electrodissolution experiments were performed with depleted uranium to understand the effects of various operating parameters. Sufficient precipitate was also produced to evaluate the feasibility of using ultrafiltration to separate the uranium oxide precipitates from the electrolyte before it enters the decontamination fixture. In preparation for the experiments, a potential-pH diagram for uranium was constructed from thermodynamic data for fully hydrated species. Electrodissolution in unstirred solutions showed that uranium dissolution forms two layers, an acidic bottom layer rich in uranium and an alkaline upper layer. Under stirred conditions results are consistent with the formation of a yellow precipitate of composition U03.2H,0, a six electron process. Amperometricexperiments showed that current efficiency remained near 100% over a wide range of electrolytes, electrolyte concentrations, pH, and stirring conditions. INTRODUCTION The United States has initiatedremoval of 200 tons of fissile material from its nuclear weapons stockpile. Oak Ridge enriched uranium (oralloy) constitutes a significant portion of the material for decontamination and consolidation. Los Alamos scientists at the Plutonium Facility have developed an electrolytic process for removing a 1-10 pM-thick layer of oralloy by electrodissolution. Under neutral to alkaline conditions, significant quantities of plutonium and americium contaminants are removed and tend to remain with the oralloy precipitate. Within the electrolytic process, electrolyte containing the precipitate is recirculated to the high velocity stream of wash water removes remaining precipitate from the oralloy part. decontamination fixture where electrodissolution takes place. After electrodissolution is complete, a 1