Vibration and wear in steam generator tubes following chemical cleaning. Final report. Volume 2

The buildup of magnetite in the steam generators of some pressurized water reactors (PWRs) has led operators to propose chemical cleaning to remove this product. In some cases, the volume of magnetite formed by the corrosion of the carbon steel has been sufficient to cause ''denting'' or reduction of the outer diameter of the tubes where they pass through the support plates. A profilometry examination of the retired Surry 2A steam generator, conducted at Hanford by Babcock and Wilcox, revealed an average dent in the 40- to 50-mil range, with some tube diameter reduction down to 0.470 inch. In addition, when the magnetite is removed by a chemical cleaning process, the diameter of the hole in the tube support plate is increased even further. The US Nuclear Regulatory Commission (NRC) has expressed concern that an increased clearance between the tube and the tube support plate may result in an increased level of flow-induced vibrations in chemically cleaned steam generators, in cases where the tube support plates are exposed to the cleaning process. This may, in turn, lead to high tube wear rates and unacceptable levels of tube failure. The Pacific Northwest Laboratory (PNL) is supporting the NRC staff in addressingmore » the effects of increased tube/tube-support clearances. The objective of PNL's work is to provide NRC with criteria with which to evaluate licensees' specific proposals for chemical cleaning of steam generators.« less