United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 97-45: Environmental Qualification Deficiency for Cables and Containment Penetration Pigtails

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

                                 July 2, 1997

                                 
NRC INFORMATION NOTICE 97-45:  ENVIRONMENTAL QUALIFICATION DEFICIENCY          
                               FOR CABLES AND CONTAINMENT PENETRATION          
                               PIGTAILS


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 a potential environmental qualification (EQ)
deficiency for cables and containment penetration pigtails.  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 to this notice
is required. 

Description of Circumstances

While investigating high-range radiation monitor (HRRM) output fluctuations,
Southern California Edison (the licensee for the San Onofre plant) noted that
the monitor output appeared to be affected by environmental factors
(temperature, air flow, electronic noise, and so on).  Accordingly, Southern
California Edison initiated additional EQ testing to reassess the
environmental qualification of the HRRMs and signal cables.  HRRMs provide
information to assist plant operators in diagnosing and responding to events.

For the EQ reassessment testing, Southern California Edison conducted steam
chamber tests for the Rockbestos RSS-6-104/LE coaxial cable and the Amphenol
(N) style connector combination used for the HRRMs.  On June 11, 1996,
Southern California Edison concluded that moisture could permeate the HRRM
coaxial cable jacket during an accident and cause partial shorting of the
monitor signal at the penetration pigtail connectors.  Because of the
extremely small signal current output from the HRRMs (nominally, pico-
amperes), this partial shorting of the signal would be sufficient to cause the
HRRMs to be inoperable.

Based on the results obtained from additional testing, Southern California
Edison replaced the organically insulated cable and penetration pigtails
inside containment at San Onofre  Unit 2 with stainless steel jacketed,
mineral insulated cable and solid conductor containment electrical
penetrations.  Testing of the new equipment configuration confirmed that EQ
requirements for this application were satisfied.  Similar repairs for San
Onofre Unit 3 will be completed during its Cycle 9 refueling outage.

9706260302.                                                            IN 97-45
                                                            July 2, 1997
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Discussion

In Licensee Event Report (LER) Number 96-005-01 (Accession No. 9702130104),
Southern California Edison indicates that lack of integrated testing of the
system as a whole may have contributed to the above-described EQ deficiency. 
During initial plant licensing, EQ testing for the HRRMs, signal cables, and
terminating connectors was performed on the discrete components and each
discrete component satisfied its specific EQ acceptance criterion (insulating
integrity).

The geometric configuration of cable/connector/penetration assembly
combinations used to connect HRRMs may also contribute to potential
environmentally induced failures.  At  San Onofre, the cable runs for the four
HRRMs (two in each unit) vary from 175 to 250 feet inside containment.  Of
this length, a maximum of 90 feet is exposed in cable trays, with the
remaining cable routed through unsealed conduit.  The HRRMs are installed at a
45-foot higher elevation than the containment penetration assemblies
(Westinghouse Model WX-32916).  As indicated in the above LER, during a
loss-of-coolant accident and after permeating the cable jacket, moisture could
form a water column inside the cable jacket and be forced into the containment
penetration connector by the 45-foot pressure head developed by the cable
elevation change.  Further, the containment penetration assembly pigtails
themselves use a cable similar to the HRRM cables.  In discussions with the
licensee regarding the similarities between the Rockbestos coaxial cable and
the containment penetration pigtail cable, the licensee indicated that the
jackets for both cables are identical in construction, thickness, and
material.  The jacket material for both cables is radiation cross-linked flame
retardant non-corrosive modified polyolefin.  In addition, the shield material
underneath the jackets of both cables is very similar and the shield
construction is the same.  Thus, moisture could similarly permeate their
jackets and short circuit the containment pigtail connector.  This partial
shorting of the circuit could result in the loss of the HRRM function.

In addition to HRRM circuits, the above mentioned cables may be used in other
monitoring system applications.  Further, the above mentioned penetration
pigtails may also be used in other safety-related equipment applications. 
Failure or degradation of these items during or following design-basis
accidents could significantly affect the functional performance of
safety-related equipment.  

In Information Notice 93-33, "Potential Deficiency of Certain Class 1E
Instrumentation and Control Cables," dated April 28, 1993, the NRC staff noted
that the insulation resistance of the Rockbestos coaxial cables may be too low
to meet specifications for use in General Atomics radiation monitor circuits,
depending on the environment to which the cable will be exposed.  The low
insulation resistance of these Rockbestos coaxial cables was the subject of a
10 CFR Part 21, "Reporting of Defects and Noncompliance," notification by
General Atomics dated March 28, 1989.

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                                                            July 2, 1997
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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.   

                                          signed by S.H. Weiss for
        
                                    Marylee M. Slosson, Acting Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation 

Technical contacts:  Duc T. Nguyen, NRR
                     301-415-3202
                     E-mail:  dtn1@nrc.gov

                     Frank S. Ashe, NRR
                     301-415-2785
                     E-mail:  fsa@nrc.gov

                     T. Jerrell Carter, NRR
                     301-415-1153   
                     E-mail:  tjc@nrc.gov
Page Last Reviewed/Updated Tuesday, December 03, 2013