Study on the Deposition Behavior of 690TT Alloy Corrosion Products in the Simulated Oxidation Operation Stage of PWR

Abstract

In order to control the radiation source term and reduce the collective dose during overhaul， the characterization methods such as scanning electron microscopy，focused ion beam transmission electron microscopy and positron annihilation were employed to study the effects of the oxidation operation process on the deposition behavior of corrosion products on the surface of the 690TT alloy in the steam generator of typical equipment.Results showed that a double-layer oxide film structure was formed on the surface of the 690TT alloy sample after pretreatment.The outer oxide layer was composed of nickel ferrite NixFe3－x O4， and the inner oxide layer was composed of chromium rich spinel NixFeyCr3－x－yO4.After short-term acid shutdown and oxidation operation， the sample exhibited a cross-sectional structure of the substrate， inner oxide film， outer oxide film and sediments.The inner oxide layer was chromium-rich， the outer oxide layer was partially dissolved， and the sediments were metallic nickel.During the oxidation operation stage， the solubility and redox status of metal elements on the sample surface were changed， promoting the dissolution of nickel ions on the sample surface， inhibiting the deposition of nickel elements on the sample surface， and significantly reducing the amount of sediments.Based on the experimental results， a dissolution deposition model on the surface of nickel-chromium-iron alloy was established.

Keywords

• alloy 690tt|oxidation operation|corrosion products|deposition