Corrosion in Nuclear Power Plant (Water Chemistry (• Chemical interaction…
Corrosion in Nuclear Power Plant
• Chemical interaction between the materials and H2O causing: material degradation + consequences problem on the component.
• Water chemistry impact both corrosion and stress corrosion cracking (SCC) of RCS material.
• Corrosion – oxidation process that occur uniformly over a material surface.
• Corrosion product release from system surface will form deposit on the FE.
• i.e. : Co-58 and Co-60 – lead to increase plant radiation level.
Primary Water SCC
• PWSCC occur when there are a present of high tensile stress, primary water environment and susceptible microstructure simultaneously.
• PWSCC of CRDM – lead to boric acid corrosion of the RPV which resulting to primary water leak (significant impact on plant safety).
• To prevent the SCC of authentic stainless steel - minimise Oxygen and Halide concentration
• Oxygen (↓), electrochemical corrosion potential (↑), alloy susceptibility (↑)
• Factors of PWSCC
high coolant T
high residual stress
susceptible alloy microstructure
• Counteracting the corrosive effect of boric acid and minimizing corrosion in SG
Stress Corrosion Cracking (SCC)
• SCC- crack initiation and sub-critical crack growth of susceptible alloy under the influence of tensile stress and the presence of corrosive medium
Dissolved Oxygen and Hydrogen
• Oxidizing condition would lead to increased formation and transport corrosion product, higher radiation, crud build up on fuel, increased corrosion of fuel rod and increased susceptibility of material – SCC.
• Coolant O2 concentration (↓): SCC(↓)
• Controlled O2 by using hydrazine/hydro
• Chloride induced SCC occur when austenitic stainless steel are exposed to chloride ion