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Information Notice No.80-29 - Broken Studs on Terry Turbine Steam Inlet Flange
SSINS No.: 6835 Accession No.: 8006190028 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 August 7, 1980 Information Notice No. 80-29 BROKEN STUDS ON TERRY TURBINE STEAM INLET FLANGE When removing the governor and stop valve on the Unit 1 steam driven emergency feedwater pump at Arkansas Nuclear One for repair of a steam leak at the steam inlet flange Arkansas Power and Light discovered that five of the eight studs securing the flange were broken. The cause of the stud failure is unknown at this time. Metallurgical evaluation of the failed bolting will be performed to identify the mode of failure. The failed studs are 3/4 in. diameter by 3-1/2 in. long and are thought to be of ASTA-193 grade B7 steel. The turbine flange bolting is generally covered with insulation and not visible for inspection. From the information available, the bolting has not been removed or inspected since installation seven to eight years ago. The steam driven emergency feedwater pump turbine at ANO-1 is a type G turbine manufactured by the Terry Steam Turbine Company of Hartford, Connecticut. The turbine is rated at 680 BHP and 3560 RPM. The turbine operates at a reduced steam pressure of 270 psig and temperature of 400
F and has previously experienced overspeed trips and vibrations which may have been caused by slugs of water from the piping. Licensees are encouraged to carefully examine insulation in the flange to turbine casing region for evidence of leakage and consider inspection of the turbine steam inlet flange bolting. Further, during surveillance testing, care should be taken to observe if abnormal vibration or other transients occur which could promote loss of bolting integrity. This Information Notice is provided as an early notification of a possibly significant matter that is still under review by the NRC staff. It is expected that recipients will review the information for possible applicability to their facility. No specific action or response is requested at this time. If you have any questions regarding this matter, please contact the Director of the appropriate NRC Regional Office.
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