United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 77-07: Containment Electrical Penetration Assemblies at Nuclear Power Plants under Construction

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF INSPECTION AND ENFORCEMENT
                            WASHINGTON, D. C. 20555

                               December 19, 1977

                                                IE Bulletin No. 77-07   
                                                          Page 1 of 3

CONTAINMENT ELECTRICAL PENETRATION ASSEMBLIES AT NUCLEAR POWER PLANTS
UNDER  CONSTRUCTION

Description of Circumstances:

On October 3, 1977, Northeast Nuclear Energy Company reported to the NRC 
Region I Office that two control valves installed inside containment at 
Millstone Unit No. 2 demonstrated abnormal operational characteristics.
The  licensee reported that an unexpected closure of a letdown flow stop
valve  occurred. While investigating this problem the normally closed
safety  injection recirculation return line drain valve was found to be
in the open  position. Investigation of these events revealed the cause
for failure to be  electrical shorts between conductors within a
containment low voltage  penetration assembly.

The licensee subsequently determined that the wiring for both of the
valves  shared the same low voltage module in an electrical penetration.
Electrical  tests by the licensee revealed that 15 of the 85 conductors
in the suspect  connector module exhibited decreased insulation resistance
between conductors.  Based on this finding it is believed that an
electrical path between adjacent  circuits in the connector module was
established. This resulted in spurious  operation of the valves. Similar
resistance checks performed on the remaining  low voltage modules within
the affected penetration assembly revealed 17  additional conductors with
reduced insulation resistances. All conductors with  resistances less than
20 megohms were disconnected and their circuits were  reconnected through
spare conductors.

Examination of the three remaining low voltage penetration assemblies 
identified 7 additional conductors with resistances of less than 20
megohms.  Each of these circuits was also reconnected through a spare
conductor.

Investigation showed that the reduced insulation resistance was probably 
caused by moisture accumulation within the penetration assembly together
with  small fissures in the epoxy seals surrounding each conductor in the
module.  The licensee believes that moisture penetrating these cracks
reduced the  insulation resistance between adjacent


.  

                                                  IE Bulletin No. 77-07 
                                                      December 19, 1977 
                                                            Page 2 of 3

conductor. To prevent further degradation from moisture buildup within the 
penetration assemblies, the licensee re-established a dry nitrogen
pressure of  24 psig in the penetrations.

Subsequently, the licensee reported that a second event of a similar
nature  occurred on October 14, 1977. In this instance, the sample
isolation valve for  the pressurizer surge line failed to close on
command. Investigation into this  event indicated that electrical shorts
between conductors due to a moisture  accumulation problem were the
probable cause for valve misoperation. The  shorted wires were
disconnected and the valve was de-energized in the closed  position.

In discussions on the issue with the licensee and the electrical
penetration  vendor, General Electric Company, NRC staff determined that
maintenance of  nitrogen pressure is essential to the integrity of both
high and low voltage  penetration assemblies. The General Electric Company
specifies in its  penetration assembly maintenance and operation manual
that a 15 psig dry  nitrogen pressure should be maintained on low voltage
units while 30 psig  should be maintained on high voltage units.

Action To Be Taken By Applicants Of All Power Reactor Facilities With a 
Construction Permit:

Containment Electrical Penetrations - For safety related systems

1.0  Do you have containment electrical penetrations that are of the    
G. E.  Series 100, or are otherwise similar in that they depend upon an
epoxy sealant  and a dry nitrogen pressure environment to ensure that the
electrical and  pressure characteristics are maintained so as to ensure
the functional  capability as required by the plant's safety analysis
report; namely, (l) to  ensure adequate functioning of electrical safety-
related equipment and (2) to  ensure containment leak tightness? If you
do use penetrations of this type at  your facility describe the
manufacturer and model number of these units.

1.1  If you do not have penetration assemblies of the type(s) referenced
in  Item 1.0 above, describe the type(s) of penetrations, e.g.,
manufacturer and  model number now in use or planned for use in safety
systems at your facility.


  

.

                                                  IE Bulletin No. 77-07 
                                                      December 19, 1977 
                                                            Page 3 of 3

1.2  Do the transition connector pins imbedded in the epoxy as discussed
in  Item 1.0 above, have an insulation jacket?

2.0  For those penetrations referenced in Item 1 above, has the
manufacturer's  prescribed nitrogen pressure been maintained at all times
during shipping,  storage and installation?

3.0  Is there a need, as determined by either the vendor or yourself, to 
maintain penetrations pressurized during normal operation, to assure 
functionability during a LOCA.

3.1  What measures have you taken to ensure that penetrations of this type
will  perform their design function under LOCA conditions? (design
reviews, analyses  or tests)?

3.2  Are the measures that provide this assurance adequate to satisfy the 
Commission's regulations (GDC 4, Appendix A to Part 50; QA Criteria,
Appendix  B to Part 50)?

4.0  Provide your response to Items 1.0 through 3.2 above in writing
within 30  days. Responses should be submitted to the Director of the
appropriate NRC  Regional Office. A copy of your response should be
forwarded to the U. S.  Nuclear Regulatory Commission, Office of
Inspection and Enforcement, Division  of Reactor Construction Inspection,
Washington, D. C. 20555.

Approved by GAO, B180225 (R0072); clearance expires 7-31-80. Approval was 
given under a blanket clearance specifically for identified generic
problems.


  

Page Last Reviewed/Updated Tuesday, July 23, 2013