Characterisation of Particulate Material in PWR Primary Coolant

摘要

The corrosion of primary circuit components in a PWR is the precursor to a variety of issues that affect the performance and safe operation of a nuclear power plant, including radiation field build up and reduced hydrodynamic performance. In order to minimise these issues, the corrosion products that form must be isolated and characterised, to identify their stability and also possible mitigating actions. In this work, the primary water coolant was simulated using a stainless steel refreshed autoclave loop fitted with a water chemistry control system to accurately control the dissolved gasses, conductivity, Li and B additions. A series of complementary techniques have been employed to characterize the primary water coolant chemistry and particulate content. Using ex-situ ultra-filtration techniques with cooled water, it was possible to separate corrosion related particulate material that had formed. This was followed up by high resolution environmental electron microscopy, which identified the presence of clusters of iron rich colloids of about 100 nanometres in dimension. Zeta-potential analysis was performed using a zeta sizer at room temperature and suggested a negative zeta potential at typical operating conditions. The effect of these suspended particles on corrosion deposition in a primary circuit was also investigated in relation to corrosion deposition on externally polarized samples. The polarization was used to simulate the effect of electrochemical corrosion potential that could be induced by an accelerating flow whilst decoupling the effect of flow from electrochemical corrosion potential. High resolution microscopy combined with Raman spectroscopy showed that increasing the electrochemical potential at the surface of the sample caused a transition from highly particulate magnetite to a completely crystalline surface of haematite. The implication on the electrophoretic behaviour of the particulate materials is also discussed.