Document: NUREG-0800
Document ID: 48fcca4d-4efe-4600-b4ca-9911efb87843
Document Type: srp
Title: and 5.2.1.2.
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070446.pdf
Revision Date: 2023-06
Chapter: 5
Section ID: 5.2.1.1
CFR Part: 
CFR Title: 

Content:
ectives are generally met by providing water treatments to remove impurities from the secondary side water, operation procedures to remove accumulated sludges and insoluble impurities from generators, design of equipment to prevent impurities from entering the system with makeup water and design factors to prevent the impurities from concentrating and forming sludges or deposits, especially in crevices. Less than thoroughly effective water treatment, operational procedures, and design factors have led to the degradation of steam generator tubing, as documented by an extensive history of stress corrosion cracking, wastage, and denting of steam generator tubing in operating PWRs, has developed. Therefore we recommend the following criteria. 68 II. BRANCH TECHNICAL POSITION69 1. Crevices between the tubing and the tube sheets or tubing supports should be minimized to prevent concentration of impurities or solids in these areas. To achieve this goal the tubes at the tube/tube sheet interface should be expanded for the full depth of the tube sheet. To minimize the deposition of corrosion products and sludge between the tubes and the supporting structure, the tube/tube support interface should be designed to promote high velocity water flow at the interface. This would improve the "washing" of this area. 2. Regulatory Guide 1.37 endorses ANSI N45.2.1 and states in part, "The surface (of components) shall appear metal clear. Scattered areas of rust are permissible provided the aggregate area of rust does not exceed two square inches in any one square foot area." Experimental work has shown that a porous packing of oxide in the tube support 70 annulus is one of the conditions resulting in the concentration of contaminants which leads to runaway corrosion of the tube support plate. Nuclear plant operators should start up the steam generators with "metal clean" surfaces. A method of confirmation such as photographing the inside of the steam generator should be undertaken