Modelling of radiolytic production of HNO3 relevant to corrosion of a used fuel container in deep geologic repository environments

Abstract

Copper-coated steel containers are part of the engineered barrier system to permanently store Canadian nuclear fuel waste in a deep geological repository. This work models the dose rates (DRs) at the container surfaces as a function of fuel age. It also utilises a humid-air radiolysis model to study the effects of DR and humidity on radiolytic oxidant production for conditions where unexpected early water intrusion reaches clay seal materials. Radiolysis of humid air produces HNO3. The HNO3 production rate in a condensed water droplet formed on a container surface was conservatively estimated by assuming that every •OH produced by primary radiolytic processes was immediately converted to HNO3 in the gas phase and that all of the HNO3 was absorbed in the water droplet. Also assuming that all of the nitric acid absorbed in the water droplet is consumed in corroding copper and using a hemispherical water droplet geometry, the corrosion depth of the copper coating induced by humid-air radiolysis is conservatively estimated to be 9.4 μm over the permanent storage time. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.