United States Nuclear Regulatory Commission - Protecting People and the Environment

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 
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 Tuesday, November 12, 2013