United States Nuclear Regulatory Commission - Protecting People and the Environment

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
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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
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                                                            Page 4 of 5


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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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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