Corrosion Behaviour of AGR SIMFUELS

Abstract

Pure UO2 pellets and, for the first time, AGR SIMFUEL pellets simulating 25 (pellet interior) and 43 GWd/tU burn-up (rim structure) have been fabricated. Using combined electrochemical and Raman spectroscopic studies, we have investigated the effect of the AGR SIMFUEL dopants on the structure of the UO2 crystal matrix and studied the effect of H2O2 on the SIMFUEL surface as a simulant for the effect of α radiolysis of water within intruding groundwater in the near field. Preliminary results of electrochemical studies of AGR SIMFUEL samples held in direct contact with the AGR fuel cladding material, 20/25/Nb stainless steel, in modified simplified groundwater (10 mmol dm-3 NaCl, 2 mmol dm-3 NaHCO3, pH 6.8) indicate that the open circuit potential of the coupled system is (i) negative of that adopted by the isolated SIMFUEL and (ii) positive of that adopted by the isolated cladding in electrolytes of the same composition. This implies that the SIMFUEL is protected against corrosion at the expense of the steel cladding, an observation that is currently the subject of further work in our laboratories.