Radiation effects and surrogate radionuclide behaviour during the electrochemical oxidation of aqueous organic waste

  • Thomas Unsworth

Student thesis: Doctor of Engineering


Organic liquid wastes produced by the civil nuclear industry are often contaminated with radionuclides. These wastes must be consigned to a repository for long-term storage or pre-treatments like incineration can be carried out to eliminate the organic component. This can be costly, inefficient or harmful to the environment. Waste owners have sought alternative technologies to break down their organic wastes. Established processes used in other industries like water treatment and innovative solutions like the Arvia(TM) Process aim to provide a cheaper and cleaner replacement for incineration. At this point in time there has been little research into understanding the negative effects of radiation on the Arvia(TM) Process and the fate of radionuclides in the post-treatment effluent. The research carried out in this EngD project was focused on two experimental themes. Firstly, monitoring the behaviour of an inactive surrogate for caesium-137 during adsorption and electrochemical oxidation of citric acid, a complexing agent used in nuclear decontamination. Secondly, gamma-ray irradiation and ion beam irradiation experiments of carbon-based Nyex(TM) adsorbent. Laboratory experiments using a bench-scale Arvia(TM) Process unit were carried out. Mixtures of citric acid and caesium chloride were used. The adsorption and breakdown of citric acid and the movement of caesium ions were evaluated. A cobalt-60 irradiator was employed to test the effect of gamma-rays (1.17 MeV and 1.33 MeV) on the adsorbent used in the system. At low doses of gamma-rays, Nyex(TM) showed little change both structurally and in performance characteristics. A noticeable effect of gamma-ray irradiation on citric acid adsorption was found at high doses. Electrokinetic migration of caesium ions across the Y-cell was measured and evaluated; the associated ion flux was increased by the presence of citric acid. A novel technique to control the migration of caesium ions was performed. We now have a better understanding of how radionuclides behave in the Arvia(TM) Process; an indication of the overall treatment efficacy of contaminated organic complexing agents; and the promising ability of Nyex(TM) to perform as intended under ionising radiation. This work could form part of a case for the application of the Arvia(TM) Process to nuclear wastes if that option is pursued. This case would benefit from more research targeted at radioactive organic wastes and the support of industry leaders seeking to employ innovative technology.
Date of Award1 Aug 2018
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorScott Heath (Supervisor) & Simon Pimblott (Supervisor)


  • Radioactive waste
  • Organic waste
  • Electrochemical oxidation
  • Nyex
  • Arvia
  • Adsorption

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