Search
Filters
Close

SCC Growth In BWR-NWC Of A Low-Alloy Steel With Intermediate S-Content Tested At K Between 50 And 70 Mpa√M

Stress corrosion cracking (SCC) of RPV steels has shown fairly quick initiation and high crack growth rates (CGRs) in simulated normal water chemistry (NWC) autoclave tests. Still the operating experience shows no known cases that reflect this high sensitivity. The bulk of these tests have been conducted on either high sulfur material, with significant dynamic loading and/or in high sulphate or chloride environments. Recent studies at PSI and GE have shown increased CGRs at 3-5 ppb chloride. This led to the limit for normal operating conditions in the EPRI BWR water Chemistry Guidelines [3,4] to be reduced from 5 to 3 ppb of chloride during the course of this project. The effects on the in-crack chemistry of test specimens vs. those of real cracks, and the effect of cladding on cracking in LAS have been debated.

Product Number: ED22-17305-SG
Author: Martin Bjurman, Elena Calota, Björn Forssgren, Johan Stjärnsäter
Publication Date: 2022
$20.00
$20.00
$20.00

The Swedish internal recirculation pump BWRs are operated with normal water chemistry (NWC). Recent laboratory observations of increased stress corrosion crack growth rates (SSCGRs) of RPV low alloy steel (LAS) in oxygenated water at 3-5 ppb chloride led to renewed interest in SCC of LAS and e.g., revision of EPRI BWRVIP-233 and BWR water chemistry guidelines. Still, limited data have beenavailable at K above 50 MPa√m for LAS plate-material sulfur contents in the upper range of the low-sulfur regime.
A plate of ASTM A533, Gr. B Class 1 with 0.011 wt.% sulfur from the archive materials of Barsebäck RPV was retrieved for SCC testing in BWR NWC environment. SCCGR testing was conducted in a multi-CT autoclave with 8 actively loaded 1.5 TCT specimens. Specimens were tested at constant K of between 50-70 MPa√m as well as with periodic partial unloading (PPU). The water chemistry was varied between 500-2000 ppb of oxygen while keeping ECP of specimens no lower than +80 mV SHE. Testing was started in clean NWC followed by a sequence of chloride transients of 3-90 ppb. Results show that CGRs are in the expected regime, though initiating and sustaining crack growth is difficult, partly due to localized growth.

The Swedish internal recirculation pump BWRs are operated with normal water chemistry (NWC). Recent laboratory observations of increased stress corrosion crack growth rates (SSCGRs) of RPV low alloy steel (LAS) in oxygenated water at 3-5 ppb chloride led to renewed interest in SCC of LAS and e.g., revision of EPRI BWRVIP-233 and BWR water chemistry guidelines. Still, limited data have beenavailable at K above 50 MPa√m for LAS plate-material sulfur contents in the upper range of the low-sulfur regime.
A plate of ASTM A533, Gr. B Class 1 with 0.011 wt.% sulfur from the archive materials of Barsebäck RPV was retrieved for SCC testing in BWR NWC environment. SCCGR testing was conducted in a multi-CT autoclave with 8 actively loaded 1.5 TCT specimens. Specimens were tested at constant K of between 50-70 MPa√m as well as with periodic partial unloading (PPU). The water chemistry was varied between 500-2000 ppb of oxygen while keeping ECP of specimens no lower than +80 mV SHE. Testing was started in clean NWC followed by a sequence of chloride transients of 3-90 ppb. Results show that CGRs are in the expected regime, though initiating and sustaining crack growth is difficult, partly due to localized growth.