"Bolting Degration or Failure in Nuclear Power Plants" (Generic Letter 91-17)

October 17, 1991 



This letter provides information on the U.S. Nuclear Regulatory Commission's 
(NRC's) resolution of Generic Safety Issue (GSI) 29, "Bolting Degradation or 
Failure in Nuclear Power Plants."  The scope of GSI-29 includes all 
safety-related bolts, studs, embedments, machine/cap screws, other special 
threaded fasteners, and all their associated nuts and washers.1  The NRC has 
resolved this issue without developing any new requirements, based on 
licensees continuing to implement actions taken in response to previous NRC 
guidance and the industry's initiatives in this area.  It is expected that 
recipients will review the information in this letter for applicability to 
their facilities and consider whether any further actions are appropriate.  
However, the suggestions contained in this letter do not constitute NRC 
requirements; therefore no specific action or written response is required.

The GSI-29 resolution encompasses a number of industry initiatives and 
previous NRC actions.  The bases for resolution are further documented in 
the enclosed NUREG-1339, "Resolution of Generic Safety Issue 29: Bolting 
Degradation or Failure in Nuclear Power Plants," which was published by NRC 
in June 1990.

The industry's initiatives on bolting include work by the Joint Task Group 
on Bolting established by the Atomic Industrial Forum (AIF), the Materials 
Properties Council (MPC), and the Electric Power Research Institute (EPRI).  
The Task Group on bolting presented its findings in a two-volume report, 

   1 Additional concerns regarding reactor vessel closure studs are being 
     addressed under GSI-109, "Reactor Vessel Closure Failure," and are 
     not considered under GSI-29. 


Generic Letter 91-17                 - 2 -

"Degradation and Failure of Bolting in Nuclear Power Plants," EPRI 
NP-5769 (2)  The Institute of Nuclear Power Operations (INPO) performed 
another study in which it recommended a number of actions in response to 
potentially unsafe bolting conditions. 

The Nuclear Management and Resources Council (NUMARC) addressed EPRI's work 
in a letter to its members on July 6, 1989, notifying them of the 
publication of EPRI Reports NP-5769 and NP-5067 (3), and stating that the 
reports provide the industry's technical basis for resolving GSI-29.  The 
letter encouraged members to refer to these reports to perform appropriate 
root cause analyses and implement proper corrective actions in response to 
NRC Bulletin 87-02, "Fastener Testing to Determine Conformance with 
Applicable Material Specifications."

Since establishing GSI-29 in 1982, the staff has issued a number of 
bulletins, generic letters, and information notices on bolting events judged 
to be safety-significant (See NUREG-1339).  The bulletins and some of the 
generic letters required both one-time actions and continuing programs.  
These actions and continuing programs were considered by the staff in 
resolving GSI-29.

Backfit Discussion

This generic letter is not considered to be a backfit because it does not 
involve any new requirements or staff positions.  The currently applicable 
requirements, in combination with actions taken in response to industry 
initiatives, are sufficient to assure integrity of safety-related bolting.  
However, because safety-related bolting may continue to pose some safety 
concerns, it is important that all licensees continue their actions in 
accordance with commitments made in response to NRC bulletins and generic 
letters on bolting events as listed in NUREG-1339. 

The NRC staff further believes that licensees can significantly improve 
safety and reduce costs by implementing the industry's recommendations 
delineated in 


   2 EPRI NP-5769 published in April 1988 proposes, among other things, 
     that bolted connections that satisfy certain criteria would exhibit 
     leakage before total failure of the connection occurred and therefore 
     should be subject to less stringent inservice inspection criteria.  The 
     American Society of Mechanical Engineers (ASME) Section XI Subcommittee 
     is reviewing a related proposal to add an ASME code case.  If the code 
     case is approved by the ASME, NRC will then consider endorsement.  
     General endorsement of EPRI NP-5769 does not imply that the NRC 
     endorses the proposed code case.

   3 EPRI NP-5067, "Good Bolting Practices, A Reference Manual for Nuclear 
     Power Plant Maintenance Personnel," volume 1: "Large Bolt Manual," 1987 
     and volume 2: "Small Bolts and Threaded Fasteners," 1990.   

Generic Letter 91-17                 - 3 -

the EPRI reports.  The staff suggests that, to efficiently implement these 
recommendations, licensees may wish to 

     (1) review the following industry-developed information:

         a.  EPRI NP-5769, volumes 1 and 24
         b.  EPRI NP-5067, volumes 1 and 24 
         c.  EPRI videotapes, "Pressure Boundary Bolting Problems," 
             parts I, II and III5

     (2) review the NRC staff report, NUREG-1339, which 
         discusses the NRC's evaluation of, and exceptions to, 
         EPRI NP-5769. 

The staff agrees that an effective means of ensuring bolting reliability, as 
recommended in EPRI NP-5769, would be to develop and implement 
plant-specific bolting integrity programs that encompass all safety-related 
bolting.  NUREG-1339 includes recommendations and guidelines for the content 
of a comprehensive bolting integrity program.  EPRI NP-5769 provides 
additional details on bolting integrity.  The plant-specific bolting 
integrity program could incorporate licensee's commitments for continuing 
actions made in response to the previously issued NRC bulletins and generic 
letters listed in NUREG-1339. 

The information in this letter does not constitute NRC requirements.  
Therefore, no specific action or written response is required.  In this 
generic letter, the staff considers the broad safety issue of bolting 
degradation or failure resolved.  However, additional regulatory actions may 
be warranted if specific problems concerning safety-related bolting should 
occur in the future.  If you have any questions about the information in 
this letter, please contact one of the technical contacts listed below. 


    4 Requests for copies of EPRI reports NP-5769 and NP-5067 should be
      directed to Research Reports Center, P.O. Box 50490, Palo Alto, CA  
      94303, (415) 965-4081.

    5 These videotapes are available from EPRI NDE Center, P.O. Box 217097, 
      Charlotte, NC 28221, (704) 547-6110


Generic Letter 91-17                 - 4 -

This generic letter contains no information collection requirements and 
therefore is not subject to the requirements of the Paperwork Reduction Act 
of 1980 (44 U.S.C. 3501 et seq.)


                                 James G. Partlow
                                 Associate Director for Projects
                                 Office of Nuclear Reactor Regulation


Technical Contact(s):    R. E. Johnson, RES
                         (301) 492-3909

                         T. Y. Chang, RES
                         (301) 492-3922

                         J. A. Davis, NRR
                         (301) 492-0713

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