Surface Electrochemistry of UO₂ in Dilute Acidic Hydrogen Peroxide Solutions

Abstract

Prospects for long-term disposal of spent nuclear fuel in geologicalr epositories are very good, although it is possible that container failure due to fabrication errors could lead to ground water entering the vessel and contacting the fuel wasteform. Alpha radiation fields, which persist for a long time, could lead to formation of the powerful oxidant hydrogen peroxide through water radiolysis. The electrochemical reduction of hydrogen peroxide on SIMFUEL (doped uranium dioxide) displays a pH dependence over the range 1-3. Cyclic voltammetry was used to determine that at pH < 2.6, hydrogen peroxide reduction is catalyzed by adsorbed UV-containing surface layer while at pH > 2.6 hydrogen peroxide reduction is catalyzed on a UV-containing surface lattice layer. It has been observed that as the peroxide concentration is decreased, the low pH mechanism persists at higher pH values. This can be attributed to the relative stabilities of these layers as facilitated by OH- ions in solution and pHl ocalization at the electrode surface.