Information Notice No.80-29 - Broken Studs on Terry Turbine Steam Inlet Flange
SSINS No.: 6835
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
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
400F 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.
Page Last Reviewed/Updated Thursday, March 25, 2021