Localized Corrosion of Nuclear Grade Alloy 800 Under Steam Generator Layup, Startup and Operating Conditions

Abstract

The localized corrosion resistance of nuclear-grade Alloy 800, which is one of the preferred steam generator (SG) heat exchange tube materials of CANDU and PWR reactors, was studied under simulated SG secondary side crevice chemistry conditions at ambient temperature as well as at elevated temperatures. Series of cyclic potentiodynamic polarization tests were performed to study the localized corrosion resistance of Alloy 800 as a function of chloride ion concentration in the SG crevice solution at 40°C, 150°C and 300°C. Based on the experimental results, empirical equations were provided for calculating the pitting potential of nuclear grade Alloy 800 in the SG secondary side crevice chemistries with different levels of chloride concentration at SG layup, startup and operating temperatures.

Understanding the interaction of thiosulfate with Alloy 800 in aqueous chloride solutions using SECM

“…Alloy 800 is one of the materials used for steam generator (SG) tubing in CANDU Ò ™ (CANada Deuterium Uranium) nuclear power stations and is also used in other pressurized water reactor (PWR) SGs due to its proven excellent corrosion resistance [1][2][3]. However, impurities on the SG boiling side, such as sulfate, chloride and lead, may collectively cause passivity degradation of Alloy 800 [4].…”

Corrosion control of nuclear steam generators under normal operation and plant-outage conditions: a review

“…Atomic Energy of Canada Limited (AECL) studied the pitting corrosion susceptibility of nuclear grade alloy 800 tubing in NSGs lay-up, start-up and operating conditions (Lu 2012). The lay-up simulating conditions consisted of solutions with a mixture of NaCl, KCl and CaCl 2 with total chloride concentrations of 0.01, 0.1, 0.65, 1 or 4 mol/kg plus 0.15 mol/kg Na 2 SO 4 .…”

Convective Mass Transfer Through an Unreactive Porous Deposit Layer Under High Temperature Conditions

“…In this analysis, the diffusivity of DO in light water is obtained from a correlation developed by Wilke and Chang [14]. With the porosity of the porous media (∅), defined as, ∅ = void volume contained in porous media sample total volume of porous media sample (7) the SG deposit layer typically consists of colloidal or spherical particles and the porosity is between 0.5 and 0.7 [9]. For random sphere packings with a porosity range of 38%-43%, the diffusibility can be varied in the range of ð0.57 ± 0.04Þ∅ [13].…”

“…The transport of chemical species from the main fluid to the tube surface through a porous layer can be affected by the main flow velocity [5], temperature [6,7], and the thickness and physical properties of the porous layer (such as porosity and permeability) [8,9]. These factors will influence the convective mass transfer in the porous layer and thus affect the interfacial chemistry at the tube surface that determines the susceptibility to SCC.…”