Information Notice No. 82-06: Failure of Steam Generator Primary Side Manway Closure Studs
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
March 12, 1982
Information Notice No. 82-06: FAILURE OF STEAM GENERATOR PRIMARY SIDE
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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