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Experimental and Computational Analysis of Nitric Acid Radiolysis
[Thesis]. Manchester, UK: The University of Manchester; 2020.
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Abstract
Nitric acid is exposed to a variety of radiation sources at various stages of the nuclear fuel cycle, causing the destruction of the nitric acid molecule and the production of various reactive nitrogen and oxygen containing species, such as NO3â€Â¢, â€Â¢Oâ€Â¢ and NO2â€Â¢. These, in turn, can react with water radiolysis products creating products such as nitrous acid, hydrogen peroxide and potentially dangerous gases such as H2 and NOx. Their production results in the de-acidification and de-nitrification of the solutions and can disrupt and degrade sealed systems with increased pressure and container damage. As nitric acid is a key component in the PUREX process and present in HAL storage tanks (HASTs), in which the chemical disruption of the solution can lead to the precipitation of radioactive isotopes and the destruction of nitric acid produced pacification layers on the stainless-steel containers, compromising their structural integrity. Whilst the consequences of nitric acid radiolysis are known, the specific radiolytic processes important in long-term irradiation are less understood and studied. A computational model of nitric acid radiolysis was attempted, though the complexity of nitric acid radiolysis resulted in a model that was limited in relevance. Experimental data was collected to support the modelling process, but due to the distinct lack of literature data was a far more involved process than initially thought and became the main focus of this project.