Information Notice No. 88-89: Degradation of Kapton Electrical Insulation
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
November 21, 1988
Information Notice No. 88-89: DEGRADATION OF KAPTON ELECTRICAL INSULATION
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to a potentially
generic safety problem involving Kapton aromatic polyimide electrical
insulation. Kapton is used extensively in nuclear power plants as wire
insulation in con-tainment penetrations and cable entrance seals manufactured
by Conax Buffalo Corporation, and in various insulation systems in products
supplied by other vendors. Kapton is a registered trademark of E. I. du Pont
de Nemours and Company.
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:
Problems involving Kapton insulation have been reported at nuclear power
plants and elsewhere as described below. The most significant event
identified in the nuclear industry occurred at San Onofre Unit 1.
San Onofre Nuclear Generating Station Unit 1
On June 15, 1987 Southern California Edison Company advised the NRC of a
problem involving damaged Kapton insulation on containment electrical
penetration assemblies at San Onofre Unit 1. During electrical testing of
control rod drive equipment circuits to determine if previous cooling fan
malfunctions had caused any damage, unacceptably low insulation resistances
were found on 35 circuits. In one penetration assembly alone, 11 circuits
tested below one megohm and 11 others below 100 megohms. The licensee then
visually inspected the approximately 5000 penetration leads in the plant, and
discovered nicked insulation in 52 cables covering close to 200 circuits.
Most of the defects were outside containment; 15 nicked leads were inside
containment.
8811150088
. IN 88-89
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Page 2 of 5
Laboratory analysis of two damaged leads showed no signs of electrically
induced damage, and the insulation edges at the breaks were smooth (suggesting
moderate chemical attack). The damage sites were highly localized; adjacent
insulation showed no degradation. The copper conductor was oxidized
considerably.
As a short-term corrective action, the licensee replaced all safety-related
wires showing any signs of degradation or damage. Longer-term corrective
action, now partially completed, includes provision of cable tray covers;
replacement of nicked non-safety-related cables; and administrative and
procedural measures such as personnel training and written precautions
concerning unprotected Kapton-insulated wires. This event is described in
Licensee Event Report 05000205 87-008-00, dated July 10, 1987.
The licensee attributed the damage primarily to physical damage (cuts, punc-
tures, abrasions) to exposed Kapton insulation, mainly during installation of
the replacement penetration assemblies in 1985-86. Some damage was attributed
to subsequent stepping on the wires and placing or dropping objects on them.
Once the Kapton insulation was penetrated, condensation of marine air on the
outside containment pigtails provided a conductive path that lowered
insulation resistances. The extensive replacement of containment electrical
penetration assemblies such as occurred at San Onofre Unit 1 is uncommon, and
it contributed to the exposure of unprotected Kapton leads to mechanical
damage. Exposure of the Kapton leads to an outside marine atmosphere is also
unusual.
Other Kapton Concerns
(1) Information Notice 87-08 (reference 1) describes 1986 failures of
motorized valve operators because wires insulated with Kapton/Teflon and
Nomex short-circuited. The Kapton/Teflon was a 0.0012-inch tape
overlapped 50-percent. These wires were subjected to abrasion damage
during wiring of the valve operators.
(2) Information Notice 87-16 (reference 2) describes 1987 degradation of
Kapton diaphragms in pressure switches caused by chemical attack by
ammonia con-tained in the process fluid.
(3) In 1984 Gulf States Utilities filed a 10 CFR 50.55(e) report concerning a
short circuit between two Kapton-insulated wires from Conax penetration
assemblies at River Bend Station Unit 1. The condition occurred during
plant construction, and inspection showed 15 of 201 conductors to have
nicked or otherwise damaged insulation. Investigation showed that degra-
dation was generally attributable to scuffs, gashes, and related damage
aggravated by the presence of water.
(4) In several instances anomalies have occurred during qualification type
testing of Kapton-insulated pigtail wires on Conax products or on other
equipment such as transmitters that had cable entrances sealed by Conax
seals. The anomalies have been attributed to handling and stresses not
typical of plant installations; e.g., shipment from a radiation test
facility to a steam test facility. Only a few wires showed degradation
in each instance, whereas multiple wires not subject to abnormal handling
have successfully completed type test sequences.
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(5) In response to Information Notices 87-08 and 87-16, du Pont wrote to the
NRC to caution that when Kapton is used in nuclear power plants where
environmental qualification is required, engineered designs which protect
Kapton from direct exposure to loss of coolant accident sprays are
required. This is because Kapton tends to degrade when exposed to high
temperature steam or to certain volatile chemicals such as sodium
hydroxide.
(6) The Naval Research Laboratory (NRL) has published or presented several
papers (references 3, 4) describing failures of Kapton-insulated wires
during laboratory testing. The Navy has carefully examined potential
problems with Naval aircraft service. As a result, The Navy intends to
stop buying aircraft using Kapton-insulated wire, and the other military
services are studying possible implementation of restrictions.
The NRL work, in conjunction with other available information, shows that
Kapton wire insulation is subject to damage by four mechanisms:
� Mechanical nicking or gouging can expose a wire conductor. Low in-
sulation resistance can occur if an electrical path to an adjacent
metallic conductor is formed by either a conductive solution or
direct metal-to-metal contact. The San Onofre Unit 1 event is of
this type.
� Direct chemical attack by strong alkaline solution can dissolve
Kapton. This process would be of concern only if Kapton were
installed contrary to Conax installation instructions in plants with
sodium hydroxide spray, so that the Kapton was either exposed to
prolonged direct spray impingement or prolonged soaking in spray
solution.
� Bullets or projectiles can damage energized wire bundles. This is
not likely in commercial power plants, and related safety concerns
are minimal because of the redundancy and separation used for
safety-related equipment.
� A complex hydrolytic Kapton degradation process has been identified
with synergistic, non-linear dependence on temperature, moisture,
and mechanical strain. Test data from 60 degrees Celsius upward
show a reciprocal logarithmic temperature dependence. du Pont
(reference 5) has suggested a fifth-power humidity dependence. Wolf
(reference 6) reported a strong dependence on strain and postulated
a minimum strain of 3 to 4 percent below which degradation does not
occur. The process is almost fully reversible provided that actual
cracking has not occurred. Review of commercial nuclear power plant
applications indicates that this mechanism is not significant for
either normal or accident conditions; operating experience and type
test results support this conclusion. However, violation of minimum
bend radius requirements specified by Conax and Rosemount for their
wires, combined with significant moisture exposure and elevated
temperatures, could produce this type of damage.
. IN 88-89
November 21, 1988
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du Pont has several publications describing Kapton and its use. These may be
obtained by contacting:
Mr. Paul Wyche
E. I. du Pont Nemours and Company, Inc.
External Affairs Department N-2526
Wilmington, Delaware 19898
Phone: (302) 774-1942
Conax Seals
The major safety-related use of Kapton in commercial nuclear power plants is
in Conax products: containment electrical penetration assemblies, penetration
replacement adapter module assemblies, electrical conductor seal assemblies
(ECSAs), PL-type gland seals, and resistance temperature detector assemblies.
Conax uses Kapton-insulated wire constructed of two wraps of type FN Kapton
film, spiral wrapped in opposite directions. Since the film consists of 0.001
inch of Kapton sandwiched between two 0.0005-inch layers of Teflon (a du Pont
trademark for FEP fluorocarbon), and each wrap is overlapped 50-percent, the
total insulation thickness is 0.008 inch. The MIL-W-81381/11 wire used by the
Navy is similar except that it has a 0.002-inch dispersed Kapton topcoat.
For seal assemblies, Conax supplies a heat-shrinkable polyolefin jacket to me-
chanically protect Kapton insulation. In addition, installation manuals
caution against mechanical damage and protective conduit is also specified.
Penetration assemblies are supplied with a junction box which encloses Kapton
leads. Most other vendors using Kapton-insulated leads in safety-related
applications provide covers or enclosures (for example, Rosemount seals and
Target Rock and Valcor solenoid valves).
Discussion:
Despite the plant-specific aspects of the San Onofre Unit 1 event, the generic
lesson is that the performance of numerous Kapton-insulated wires degraded
considerably after only one year in a quite mild environment. Mechanical
damage to Kapton insulation combined with exposure to condensation of moist
salty air produced unacceptable degradation of the electrical insulation
properties.
Although Kapton-insulated pigtails have successfully completed several
accident qualification type tests, the test specimens are believed to have
been free from nicks in the insulation; further, test anomalies occurred in
some cases in which the pigtails were subjected to abnormal handling. The
lesson is that preaccident damage can lead to failure of Kapton-insulated
wires during or after accidents.
Addressees are alerted that the following conditions may breach the integrity
of Kapton insulation, leading to possible failures under either normal or
accident conditions:
(1) Mechanical damage such as nicks, cuts, abrasion, or sharp bending
combined with exposure to moisture.
(2) Prolonged contact with alkaline solutions.
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November 21, 1988
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Addressees are also reminded that excessive handling of wiring is undesirable.
In view of the industry's generally good operating experience with Kapton,
addressees may elect to take actions in response to the information in this
notice by beginning with review of procedures and designs to determine whether
the conditions cited above may exist. Caution with any future maintenance or
installation activity involving Kapton is important.
Virtually all commercial nuclear power plants contain Kapton-insulated wires
in safety and non-safety-related applications, with Conax products used most
extensively. Such components as containment electrical penetration assemblies
and cable entrance seals are commonly used in Class 1E circuits and in
applications requiring qualification to 10 CFR 50.49. Failure of Kapton
insulation during either normal plant operation or accident conditions could
render associated equipment inoperable.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: Richard C. Wilson, NRR
(301) 492-0997
Attachments: 1. References
2. List of Recently Issued NRC Information Notices
. Attachment 1
IN 88-89
November 21, 1988
REFERENCES
1. Information Notice No. 87-08: "Degraded Motor Leads in Limitorque dc
Motor Operators," February 4, 1987.
2. Information Notice No. 87-16: "Degradation of Static "O" Ring
Pressure Switches," April 2, 1987.
3. F. J. Campbell, "Temperature Dependence of Hydrolysis of Polyimide Wire
Insulation," IEEE Transactions on Electrical Insulation, Vol. EI-20 No.
1, February 1985.
4. A. M. Bruning, "Predictive Life Measurements of Naval Aircraft Wiring,"
Proceedings: Workshop on Power Plant Cable Condition Monitoring, EPRI
EL/NP/CS-5914SR, July 1988.
5. J. O. Punderson and J. F. Heacock, "Polyimide Film Insulation for
Aerospace Wire and Cable: Why Long-Term Performance Exceeds Some Limited
Laboratory Projections, " presented at the 34th International Wire and
Cable Symposium, Cherry Hill, NJ, November 19-21, 1985 (available from du
Pont).
6. C. J. Wolf, D. L. Fanter, and R. S. Soloman, "Environmental Degradation
of Aromatic Polyimide-Insulated Electrical Wire," IEEE Transactions on
Electrical Insulation, Vol. EI-19 No. 4, August 1984.
. Attachment 2
IN 88-89
November 21, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-88 Degradation of Westinghouse 11/16/88 All holders of OLs
ARD Relays or CPs for nuclear
power reactors.
88-87 Pump Wear and Foreign 11/16/88 All holders of OLs
Objects in Plant Piping or CPs for nuclear
Systems power reactors.
86-106, Feedwater Line Break 11/10/88 All holders of OLs
Supp. 3 or CPs for nuclear
power reactors.
88-86 Operating with Multiple 10/21/88 All holders of OLs
Grounds in Direct Current or CPs for nuclear
Distribution Systems power reactors.
88-85 Broken Retaining Block 10/14/88 All holders of OLs
Studs on Anchor Darling or CPs for nuclear
Check Valves power reactors.
88-84 Defective Motor Shaft 10/20/88 All holders of OLs
Keys in Limitorque Motor or CPs for nuclear
Actuators power reactors.
88-83 Inadequate Testing of Relay 10/19/88 All holders of OLs
Contacts in Safety-Related or CPs for nuclear
Logic Systems power reactors.
88-82 Torus Shells with Corrosion 10/14/88 All holders of OLs
and Degraded Coatings in or CPs for BWRs.
BWR Containments
88-81 Failure of Amp Window 10/7/88 All holders of OLs
Indent Kynar Splices or CPs for nuclear
and Thomas and Betts power, test, and
Nylon Wire Caps During research reactors.
Environmental Quali-
fication Testing
88-80 Unexpected Piping Movement 10/7/88 All holders of OLs
Attributed to Thermal or CPs for PWRs.
Stratification
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
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