Companion Guide to the ASME Boiler & Pressure Vessel Code, Volume 3, Second Edition: Criteria and Commentary on Select Aspects of the Boiler & Pressure Vessel and Piping Codes
44 PWR Reactor Vessel Alloy 600 Issues
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Jeff Gorman, Steve Hunt and Pete Riccardella authored chapter 44. They have considerable expertise and experience in handling PWR Reactor Vessel Alloy 600 and related issues address the problems confronted by the industry. Considering the extreme importance of this topic the authors have covered concerns pertinent to several ramifications of the problem.
Primary water stress corrosion cracking (PWSCC) of Alloy 600 nickel-chromium-iron base metal and related Alloy 82∕132∕182 weld metal has become an increasing concern to commercial pressurized water nuclear power plants. Cracks and leaks have been discovered in Alloy 600∕82∕182 materials at a number of locations in PWR reactor vessels worldwide. These locations include control rod drive mechanism (CRDM) nozzles, bottom head instrument nozzles and reactor vessel outlet and inlet nozzle butt welds. The consequences of this PWSCC have been significant including 72 leaks (56 CRDM nozzles, 13 thermocouple nozzles, 2 bottom mounted instrument nozzles, and one butt weld), many cracked nozzles and welds, expensive inspections, more than 60 heads replaced, several plants with several month outage extensions to repair leaks, and one plant down for over two years with extensive corrosion to the vessel head resulting from a leaking CRDM nozzle. This chapter addresses Alloy 600∕82∕182 material locations in reactor vessels, operating experience, causes of PWSCC, inspection methods and findings, safety considerations, degradation predictions, repair methods, remedial measures, and strategic planning to address PWSCC at the lowest possible net present value cost.