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On August 31, 2001, with Unit 2 in Mode 1 … On August 31, 2001, with Unit 2 in Mode 1 (Power Operation) at 100 percent power, a PG&E employee investigating a steam leak discovered a broken stud on a valve bonnet for a steam generator 10 percent atmospheric steam dump valve. Investigations found the remaining seven bonnet fasteners had cracks in either the studs or nuts. On October 3, 2001, based on results from multiple Charpy impact tests of fasteners in similar service, PG&E concluded the material had become embrittled.</br></br>The fasteners failed due to Stress Corrosion Cracking (SCC). PG&E has determined that the SCC was caused by a combination of unanticipated high temperature embrittlement and elevated stress in the presence of corrodants.</br></br>Ten years of operation at temperatures of as low as 470 degrees F embrittled the ASME SA 564, Type 630, Condition H1100 (17-4 PH) stainless steel material, causing increased susceptibility to SCC. Higher than expected stress was presumably caused by inadequate administrative controls over the maintenance torquing practices.</br></br>Corrective actions include replacing embrittled material in plant locations where it is highly susceptible to SCC, and/or exposed to significant impact loads at low temperature. Also, maintenance practices are being revised to enhance torquing practices.</br></br>LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6)ION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) +
On August 31, 2001, with Unit 2 in Mode 1 … On August 31, 2001, with Unit 2 in Mode 1 (Power Operation) at 100 percent power, a PG&E employee investigating a steam leak discovered a broken stud on a valve bonnet for a steam generator 10 percent atmospheric steam dump valve. Investigations found the remaining seven bonnet fasteners had cracks in either the studs or nuts. On October 3, 2001, based on results from multiple Charpy impact tests of fasteners in similar service, PG&E concluded the material had become embrittled.</br></br>The fasteners failed due to Stress Corrosion Cracking (SCC). PG&E has determined that the SCC was caused by a combination of unanticipated high temperature embrittlement and elevated stress in the presence of corrodants.</br></br>Ten years of operation at temperatures of as low as 470 degrees F embrittled the ASME SA 564, Type 630, Condition H1100 (17-4 PH) stainless steel material, causing increased susceptibility to SCC. Higher than expected stress was presumably caused by inadequate administrative controls over the maintenance torquing practices.</br></br>Corrective actions include replacing embrittled material in plant locations where it is highly susceptible to SCC, and/or exposed to significant impact loads at low temperature. Also, maintenance practices are being revised to enhance torquing practices.</br></br>LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6)ION FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) +
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