Information Notice No. 92-15: Failure of Primary System Compression Fitting
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 24, 1992
NRC INFORMATION NOTICE 92-15: FAILURE OF PRIMARY SYSTEM COMPRESSION FITTING
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to problems that could result from the inadequate
installation of compression fittings. It is expected that recipients will
review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. However, suggestions
contained in this information notice are not NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances
On November 23, 1991, operators at the Oconee Nuclear Station, Unit 3,
detected unidentified leakage of approximately 70 gallons per minute (gpm)
from the reactor coolant system (see licensee event report 50-287/91-008).
The licensee shut down the reactor in an orderly manner. The licensee
observed a maximum leak rate of approximately 130 gpm and found that a total
of 87,000 gallons of reactor coolant was discharged to the containment
before the reactor coolant system could be depressurized. On November 25,
1991, personnel entered the Unit 3 containment building and determined that
the source of the leak was a separated compression fitting on a 3/4-inch
diameter instrument line. The instrument line is part of the reactor vessel
level indication system (RVLIS). The leak occurred where the line connects
to the top of the "A" steam generator hot leg. The tubing separated from
the fitting next to a 3/4-inch flow restriction valve.
The licensee inspected the fitting and determined that the probable cause of
the tubing separating (or pulling out) was that the nut had not been suffi-
ciently tightened onto the compression fitting. The nut on the fitting
appeared to have been tightened approximately 1/2 turn less than was recom-
mended by the fitting manufacturer, the Parker-Hannifin Corporation. The
gap between the nut and the fitting was greater than the maximum nominal
value furnished by the vendor. The licensee inspected the tubing at the
failed fitting and determined that the diameter reduction at that location
was much less than the diameter reduction for the tubing in another fitting
that had not failed. Based on these inspections the licensee determined
that the ferrule
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IN 92-15
February 24, 1992
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was not adequately compressed into the tubing. The licensee reconfigured
the instrument line and replaced the valve, the 3/4-inch instrument tubing,
and the fittings on the hot legs of both steam generators.
The licensee inspected all of the fittings on instrument tubing connected to
the Unit 3 primary system. The licensee examined the 264 Parker-Hannifin
fittings in the primary system using nominal expected gap values furnished
by Parker-Hannifin as an acceptance criteria. However, Parker-Hannifin does
not consider the gap to be a critical dimension. The licensee also
inspected the 191 Swagelock fittings in the primary system using gap
inspection gages furnished by Swagelock. The licensee found that
approximately 27 percent of both types of fittings appeared to have gaps
outside of the nominal range. The licensee attempted to tighten these
fittings to reduce the gaps to the values recommended by the manufacturers.
However, a small percentage of the Parker-Hannifin fittings could not be
tightened to meet the vendor's nominal gap values. The licensee accepted
these fittings as-is based on the judgement of the instrument technicians
that the connections could not be tightened further without damaging the
tubing or connections, and on an engineering evaluation made after
disassembling and inspecting one of the questionable fittings.
Discussion
This event reemphasizes the importance of making successful connections in
instrument tube lines. Fitting nuts on compression fittings must be
tightened sufficiently to ensure that the fitting has been adequately
seated. According to the licensee, they have previously experienced
problems with inadequate assembly of 3/4-inch fittings due to the high
torque required to properly seat the fittings. The licensee's modifications
to the RVLIS eliminated the use of 3/4-inch fittings on these lines.
While conducting inspections at other facilities, the NRC and licensees have
noted other problems with the installation of compression fittings,
including the following:
� Interchanging hardware from different manufacturers
� Installing the ferrules backwards in fittings, or omitting the ferrules
� Failing to bottom the tubing on the shoulder of the fitting
� Using tubing that is not cut square or that is burred, scratched, de-
formed, or contaminated with dirt, oil, or other contaminants
� Failing to adequately tighten the fitting to the finger-tight position
before making additional turns from the finger-tight position
� Failing to ensure that the tubing has not moved back out of the fitting
when the nut is tightened
These problems indicate that licensees' procedures for installing
compression fittings may not provide adequate guidance to avoid improper
assembly of the
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IN 92-15
February 24, 1992
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fittings. Procedures may also fail to address the vendor's installation
recommendations, not only for the initial installation of connections, but
also for disconnecting and retightening fittings during normal maintenance
activities. In addition, personnel who make compression fitting connections
may not be adequately trained.
Related Generic Communications
The NRC staff has previously issued Information Notice 84-55 (including
Supplement 1), "Seal Table Leaks at PWRs," to address problems associated
with compression fitting failures.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Joseph J. Lenahan, RII
(404) 331-4190
John R. Fair, NRR
(301) 504-2759
Attachment: List of Recently Issued NRC Information Notices
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