CONSIDERING COBALT INCORPORATION IN OXIDE FILM UNDER BOILING WATER REACTOR CONDITIONS

UoM administered thesis: Phd

  • Authors:
  • Samuel Holdsworth

Abstract

The phenomenon of radiation field build up-within Boiling Water Reactors (BWRs) is mainly dependent on the uptake of the highly radioactive 60Co into the surface oxide of the steel components. The incorporation of 60Co in the oxide film is strongly dependent on the type, composition and structure of the spinel-based oxide, which in turn is affected by reactor water chemistry, which further includes the oxidising potential and dissolved metal ions. The present research identifies and mechanistically investigates the oxides formed under a range of oxidising potentials, dissolved metal ion concentrations and surface finishes, using high-resolution characterisation techniques. As predicted within literature the oxides formed under hydrogen water chemistry conditions (HWC) conditions was shown to have a fine-grained Cr enriched spinel type inner oxide which contained voids while the outer layer was ferrite based. Zn injection prevented 59Co from incorporating into the oxide, which mechanistically occurs through the displacement of the Co2+ cation from the tetrahedral lattice sites within the spinel based oxide. Under Normal Water Chemistry (NWC) conditions, the inner layer was polycrystalline; however, the transpassivity of Cr formed a ferrite based inner layer which is considered less protective and contained extensive cavities/voids. The outer layer was composed of α-Me2O3 (Me: Fe, Cr and [Cr]

Details

Original languageEnglish
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Supervisors/Advisors
Award date31 Dec 2018