Information Notice No. 82-06: Failure of Steam Generator Primary Side Manway Closure Studs

                                                            SSINS No.:  6835
                                                            Accession No. 
                                                            IN 82-06 

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                               March 12, 1982

                                  MANWAY CLOSURE STUDS 

Description of Circumstances: 

The Nuclear Regulatory Commission (NRC) was notified by Maine Yankee Atomic 
Power Company and by Combustion Engineering (CE) that during routine disas-
sembly of a steam generator primary side manway at Maine Yankee, 6 of the 20
manway closure studs failed and another 5 were found by ultrasonic testing 
to be cracked.  These are 1 1/2 x 10 inch studs of SA 540 grade B 24 alloy 
steel. The studs had been exposed to boric acid from a small primary coolant 
leak and to Furmanite sealing compound (primary grade) applied in an attempt 
to seal this leak.  The studs exhibited evidence of surface corrosion attack 
possibly as result of an interaction associated with stud preload, 
lubricant, Furmanite and primary coolant leakage environment.  A 
metallurgical analysis to determine the failure mechanism is currently 
underway at CE.  The entire set of studs on the affected steam generator (SG 
#2) have been replaced and an ultrasonic examination of all primary manway 
studs on steam generator units 2 and 3 is being performed.  Further 
corrective actions are pending stud failure analysis and its applicability 
to other primary boundary closures. 

In the last few years there have been a significant number of incidents of 
failed or severely degraded bolts and studs.  Examples of the latter; 
primary coolant pump stud-bolts (Calvert Cliffs and Ft Calhoun) and steam 
generator primary manway closures studs (Oconee and ANO-1).  The failures 
described were attributed to stress corrosion cracking and corrosion wastage 
of high strength studs that are difficult to detect. 

The NRC has contacted the CE Regulatory Response Group and requested a 
review of the problem. 

This Information Notice No. is provided as an early notification of a 
potentially significant matter that is still under review by the NRC staff. 
If NRC evaluation so indicates, further licensee action may be requested.  
In the interim, we expect that licensees will review this information for 
applicability to their facilities. 

No written response to this information notice is requested.  If you need 
additional information, please contact the Regional Administrator of the 
appropriate NRC Regional Office. 

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