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**UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555-0001**

June 4, 1998

**Addressees**

All holders of operating licenses for nuclear power reactors, except those licensees who have permanently ceasedoperations and have certified that fuel has been permanently removed from the reactor vessel.

**Purpose**

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to a potentialdeficiency relating to environmental qualification of electrical cable/connection systems. It is expected that recipients willreview the information for applicability to their facilities and consider actions, as appropriate. However, suggestionscontained in this information notice are not NRC requirements; therefore, no specific action or written response to thisnotice is required.

**Description of Circumstances**

Sandia National Laboratories (SNL), under contract to NRC, tested electrical cable connections to assess their accidentperformance if they were aged more slowly (i.e., at lower temperatures and radiation dose rates) than in typical industryqualification tests and to investigate the performance of connections aged to a nominal 60-year life. The results of thistesting are contained in the report NUREG/CR-6412, "Aging and Loss-of-Coolant Accident (LOCA) Testing of ElectricalConnections," January 1998 (Accession Number 9803180097). Electrical connection test specimens consisting of conduitseals, connectors, and splices were chosen on the basis of their usage in commercial nuclear power plants. The testprogram generally followed the guidance provided in the Institute of Electrical and Electronics Engineers (IEEE) Standard323-1974, "IEEE Standard for Qualifying Class 1E Equipment for Nuclear Power Generating Stations," and IEEEStandard 383-1974, "IEEE Standard for Type Test of Class 1E Electric Cables, Field Splices, and Connections for NuclearPower Generating Stations."

Test program specimens consisted of 10 different electrical connection types: three types of conduit seals, two types ofcable-to-device connectors, three types of cable-to-cable connectors, and two types of in-line splices. Environmentalexposure for the test specimens consisted of two phases. The first phase consisted of simultaneous thermal and radiationaging for 6 months at 99 C (210 F) and a total radiation dose of 200 kGy (20 Mrad) at a dose rate of 45.6 Gy/hr (4.56krad/hr); the thermal exposure is equivalent to 60 years at 55 C (131 F) for an activation energy of 1.15 eV. Thesubsequent phase was a LOCA simulation that consisted of an accident irradiation exposure at a dose rate of 3 kGy/hr (300krad/hr) for an accident dose of 1,000 kGy (100 Mrad) sequentially followed by a simulated accident steam exposure. Thesimulated accident steam exposure test profile generally followed the typical test profile contained in IEEE Standard 323-1974. During the simulated steam exposure test, the connections were energized at approximately 110 Vdc, 0 mA, to allowfor online measurement of insulation resistance (IR). Following the steam exposure test, which did not include chemicalspray, SNL performed several types of electrical measurements. Post-steam exposure measurements performed on the testspecimens included dry IR, submerged IR, dry alternating current (ac) dielectric withstand, and submerged ac dielectricwithstand.

Five of the 10 cable connection types did not pass a post-LOCA, submerged, ac dielectric withstand test. These types werethe Conax Buffalo, Rosemount, Patel/EGS quick disconnect, Amphenol coaxial, and Litton-VEAM. In addition, all of theConax Buffalo electrical conduit seal assembly cable connection conductors and approximately half of the Litton-VEAMconnector and the Amphenol coaxial cable connection conductors did not pass a dry ac dielectric withstand test. TheConax Buffalo conduit seal assembly conductors had low IR values and the two non-grounded conductors repeatedly blew1-ampere fuses when energized at 110 Vdc. Approximately one-third of the Litton-VEAM connector and all fourAmphenol coaxial cable connector conductors had IR values below 107 ohms. The list of electrical cable connection typesincluded in the test program and the test results from the NUREG/CR-6412 report are provided in Attachment 1.

SNL has performed similar testing of electrical cables to determine the minimum insulation thickness necessary for cablefunctional performance and long-term aging degradation of cables. Results from these testing programs were provided inNRC Information Notice (IN) 92-81, "Potential Deficiency of Electrical Cables with Bonded Hypalon Jackets," datedDecember 11, 1992, and IN 93-33, "Potential Deficiency of Certain Class 1E Instrumentation and Control Cables," datedApril 28, 1993.

**Discussion**

The SNL test results provided in NUREG/CR-6412 raised potential issues relating to the long-term environmentalqualification of electrical cable/connections that did not pass a dry ac dielectric withstand test, a submerged ac dielectricwithstand test, or exhibited very low or marginal IR values. The staff reviewed the test data contained in the report andnoted that some of the tested cable/connections exhibited low or marginal IR values as early as 3 days after the start of thesimulated LOCA test exposure. It was also noted that Rockbestos Firewall III cross-linked polyethylene multiconductorand Rockbestos coaxial cables were installed by SNL on connection test specimens that were supplied to SNL without alength of cable.

Using these two nuclear-qualified cable types that were previously tested to the equivalent of 60 years helped to ensurethat the testing isolated the effects of aging on the cable connections.

The aging research study sponsored by the NRC and performed by SNL included searches of licensee event reports (LERs)to identify and review those LERs that contained information relating to cable connection aging. The results of thesesearches and reviews are provided in NUREG/CR-5461, "Aging of Cables, Connections, and Electrical PenetrationAssemblies Used in Nuclear Power Plants." In NUREG/CR-5461, SNL reported that electrical cable connections arehighly reliable devices under normal plant operating conditions, and they exhibited no evidence of significant increases infailure rate under normal operating conditions with aging. However, NUREG/CR-5461 also reports that many of thecauses of failures of electrical cable connections in accident conditions would not be detected during normal operationsbecause of the absence of high temperatures and humidities, and that the expected most important failure mode is shortingor reduced electrical isolation. These conclusions are consistent with the recorded test data results obtained during theelectrical cable connection testing in that there was no significant degradation in the measured insulation resistances of thetest specimens during the aging and accident irradiation exposures.

In addition, NUREG/CR-6412 reports post-test examination results for the tested cable connection specimens. Oneprimary reported result is that the jackets of a large fraction of the cables attached to the connections were cracked andwould allow ingress of moisture into the cable, which could then migrate into the connection. Specifically, the jackets ofthe EGS conduit seal cables were not sealed. The jackets of the NAMCO EC 210 connector cables were split open andextensively cracked. Jackets over the Kapton-insulated conductors for the Conax Buffalo conduit seal cables were notsealed. The jackets of the Okonite tape splice and Litton-VEAM connector cables were split open and cracked all the wayaround. For the EGS Grayboot connector cable, the jacket was split open and was also not sealed. Generally, the mainfunction of a cable jacket is to protect the insulation during installation. The SNL test results, however, indicate that cablejacket integrity may be important in preventing moisture intrusion at connections. Another post-test examination result wasthat the behavior of the Conax Buffalo conduct seal conductors was produced by degraded Kapton-insulated cable leads.Post-test examination results for the behavior of the Litton-VEAM connector revealed that the O-ring seals were brittleand had experienced compression set, which thereby reduced their sealing ability and allowed moisture to enter theconnector body. No explanation for the behavior of the Amphenol coaxial connector or the Rosemount 353C conduit sealwas identified during the post-test examination. Reported results also indicate that the test results for a particularconnection type should be evaluated while considering the specific application and set of environmental conditions.However, in certain nuclear power plant circuit applications, degradation or failure of electrical cable/connection systemsduring and/or following design-basis events can significantly affect the functional performance of safety-relatedequipment.

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.

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ATTACHMENT 1

IN 98-21June 4, 1998Page 1 of 1

Tested Electrical Cable Connections and Reported Test Results

passed - denotes no reported abnormalities

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