Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
April 4, 1990
Information Notice No. 90-23: IMPROPER INSTALLATION OF PATEL CONDUIT
SEALS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is intended to alert addressees to a possible safety
problem caused by the improper installation of Patel conduit seals as a
result of incorrect selection of grommets based on the wire gauge size. 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 do not
constitute NRC requirements; therefore, no specific action or written
response is required.
Description of Circumstances:
On November 6, 1989, the staff at the H. B. Robinson plant notified the NRC
that they had discovered that some of the conduit seal grommets used to seal
insulated wire conductors entering environmentally qualified instrument
housings were oversized for the application. The seals are used to prevent
moisture from entering safety-related electrical components following
loss-of-coolant accidents. Use of oversized seals may create potential
moisture intrusion paths into safety-related instrumentation inside the
reactor containment.
The problem was attributed to inadequate installation instructions that were
used when the seals were installed in 1986 and 1987. These instructions
listed the grommets by wire gauge size and gave maximum wire insulation
diameters for each wire size (see the first table, page 1, of the enclosed
EGS Bulletin 90-1). In accordance with these instructions, the seals were
selected based on wire gauge alone. However, since the insulation thickness
for a given wire gauge varies from one wire type to another, a more
appropriate parameter for choosing the correct grommet size would have been
the minimum wire insulation diameter for which a particular grommet will
achieve an effective seal. The selection of grommet size based only on wire
gauge size resulted in the installation of some grommets that were too large
to provide an effective seal. As a result, some of the seals failed
pressure tests that were designed to simulate post-LOCA pressures.
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IN 90-23
April 4, 1990
Page 2 of 2
During the investigation of the grommet leakage problem, the Robinson staff
also checked the torque on the conduit seal union nuts that are used to
compress the seals. EGS Corporation recommends that the union nuts be
torqued to 50 ft-lb (EGS Bulletin 90-1). On approximately half of the 90
seals inspected, the union nut moved about 1/4 inch when this torque was
applied. One union nut was found to be quite loose. EGS Corporation
reports that 1/4 inch of movement does not necessarily indicate a degraded
seal but recommends that the correct torque be verified on a representative
sample of installed conduit seals.
Discussion:
In order for these conduit seals to be able to function at accident
pressures and temperatures and for extended periods following an accident,
it is important that the correct installation procedures be established and
consistently applied. In this case, the installation of the seals according
to inadequate procedures could have resulted in moisture intrusion into more
than one safety component during an accident, leading to equipment failures
or the display of erroneous information to the operators.
Although the vendor's use of wire range sizes to designate the grommets
appears to have been intended as an aid in choosing the proper grommet for
the application, differences in insulation thicknesses because of
differences in insulating materials and type of application were not
accounted for by either the vendor's original instructions or the licensee's
initial installation procedures for the grommets. The necessary minimum
insulation diameter values for each grommet size were subsequently provided
by EGS Corporation, the supplier of the Patel conduit seals. These minimum
diameters are also included in EGS Bulletin 90-1.
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 NRR project
manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: T. E. Conlon, RII
(404) 331-5537
N. Merriweather, RII
(404) 331-5577
Attachments:
1. EGS Letter to NRC dated 1/2/90, Enclosing
Product Bulletin 90-1: Recent Events
Concerning Patel Conduit Seals
2. List of Recently Issued NRC Information Notices
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