"Bolting Degration or Failure in Nuclear Power Plants" (Generic Letter 91-17)
October 17, 1991
TO: ALL HOLDERS OF OPERATING LICENSES OR CONSTRUCTION PERMITS FOR
NUCLEAR POWER PLANTS
SUBJECT: GENERIC SAFETY ISSUE 29, "BOLTING DEGRADATION OR
FAILURE IN NUCLEAR POWER PLANTS" (GENERIC LETTER 91-17)
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
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
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,
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
T. Y. Chang, RES
J. A. Davis, NRR
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