Document: NUREG-0800
Document ID: 91fee075-c567-438d-bf9f-47be3177b457
Document Type: srp
Title: ENGINEERED SAFETY FEATURES MATERIALS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070453.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.1.1
CFR Part: 
CFR Title: 

Content:
f the Materials and Chemical Engineering Branch (EMCB))128 pH FOR EMERGENCY COOLANT WATER FOR PWRs A. Background To establish the minimum value of pH in post-accident containment sprays in pressurized water reactors, the Chemical Engineering Branch NRC Staff has reviewed the available information 129 and recommended the criteria listed in the Branch Technical Position below. The minimum pH value of 7.0 follows from the Westinghouse report (Ref.erence 1)130 conclusion that, in ECCS solutions adjusted with NaOH to pH 7.0 or greater, no cracking * should be observed at chloride concentrations up to 1000 ppm during the time of interest. Figure 7 of the Westinghouse report shows that the time for initiation of cracking of sensitized and nonsensitized U-bend specimens of Type 304 austenitic stainless steel in solutions of 7.0 pH having 100 ppm chloride was 7-1/2 months and 10 months, respectively. The great majority of tests reported in the Oak Ridge report, Reference 2, were performed with pH of 4.5, and only two tests were conducted with pH values other than 4.5. Some cracking was observed at pH 7.5 in the sensitized 304 stainless steel U-bend specimens after 2 months exposure to pH 7.5 and chloride concentration of 200 ppm. All of the 316 stainless steel specimens showed no evidence of cracking. Considering the fact that in U-bend specimens the material was sensitized, stressed beyond yield, and plastically deformed, we conclude that the reported test conditions were much more severe than the stress conditions likely to exist in the postaccident emergency coolant systems. We agree with the Oak Ridge conclusion that absolute freedom from failure of any complex system such as a spray system can never be guaranteed, but, by proper design, fabrication, and control of the corrosive environment, the probability of failure can be significantly reduced. Our recommended minimum pH is somewhat higher than the Oak Ridge recommendation of a minimum of 6.5. B. Branch Technical