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Title: Remedial methods for intergranular attack of alloy 600 tubing. Volume 3. Boric acid and acetic acid remedial methods. Final report

An important cause of recent tube degradation in recirculating pressurized water reactor (PWR) steam generators with open tube/tubesheet crevices is intergranular attack (IGA) of alloy 600 tubing in the crevice region. The attack appears to occur on the hot leg tubing because of high concentrations of caustic species formed from remnants of past phosphate water treatment, combined with materials from inleakage from freshwater-cooled condensers. The concept of using neutralizers to modify the aggressiveness of the crevice environment was examined. It appears that this can be accomplished by neutralizing the caustic species with an acid. Two ways to apply the acid are by off-line flushing during plant shutdown and by on-line treatment during operation. The substance that appears to be most suitable for off-line flushing is acetic acid, with boric acid as a second choice. Concentrations should be in the range of from 1000 to 5000 ppM. The addition of 1000 to 5000 ppM of a non-ionic detergent in the flush solution should improve penetration of the crevice. Use of preflush lancing to remove sludge on the tubesheet will also help by reducing acid consumption. The requirements for materials to be used in on-line treatment are more stringent because of possiblemore » interaction with other components in the secondry system. Boric acid is the only substance that has operational experience. A series of tests are proposed to investigate the behavior of acetic acid and boric acid on tubesheet sludge, on tubesheet/support plate material, and on alloy 600/tubesheet couples. Similarly, areas of uncertainty of on-line treatment with boric acid are its effect on tubesheet/support plate materials and on the rest of the secondary system. 23 refs.« less
Authors:
Publication Date:
OSTI Identifier:
5708583
Report Number(s):
EPRI-NP-4635-Vol.3
ON: TI86920389; TRN: 86-021995
Resource Type:
Technical Report
Research Org:
Babcock and Wilcox Co., Alliance, OH (USA). Research and Development Div.
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; 36 MATERIALS SCIENCE; INCONEL 600; CREVICE CORROSION; INTERGRANULAR CORROSION; REACTOR MATERIALS; PWR TYPE REACTORS; STEAM GENERATORS; TUBES; ACETIC ACID; BORIC ACID; CORROSION INHIBITORS; WATER CHEMISTRY; ALLOYS; BOILERS; CARBOXYLIC ACIDS; CHEMICAL REACTIONS; CHEMISTRY; CHROMIUM ALLOYS; CORROSION; HYDROGEN COMPOUNDS; INCONEL ALLOYS; INORGANIC ACIDS; IRON ALLOYS; MATERIALS; MONOCARBOXYLIC ACIDS; NICKEL ALLOYS; NICKEL BASE ALLOYS; NIOBIUM ALLOYS; ORGANIC ACIDS; ORGANIC COMPOUNDS; REACTORS; VAPOR GENERATORS; WATER COOLED REACTORS; WATER MODERATED REACTORS 210200* -- Power Reactors, Nonbreeding, Light-Water Moderated, Nonboiling Water Cooled; 360105 -- Metals & Alloys-- Corrosion & Erosion