United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 77-06 – Potential Problems with Containment Electrical Penetration Assemblies

                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE FOR INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555
                                     
                              November 22, 1977

                                                      IE Bulletin No. 77-06 

POTENTIAL PROBLEMS WITH CONTAINMENT ELECTRICAL PENETRATION ASSEMBLIES 

Description of Circumstances: 

On October 3, 1977 Northeast Nuclear Energy Company reported to the NRC 
Region 1 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 were also reconnected through a spare conductor. 



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IE Bulletin No. 77-06                                    November 22, 1977 

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 conductors. 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 was 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 Licensees Of All Power Reactor Facilities With An 
Operating License: 

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, (1) to ensure adequate functioning of electrical 
     safety-related equipment and (2) to ensure containment leak tightness? 

1.1  Have you experienced any electrical failures with this type of 
     penetration? 



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IE Bulletin No. 77-06                                    November 22, 1977 

2.0  For those penetrations referenced in Item 1 above, have you maintained 
     the manufacturer's prescribed nitrogen pressure at all times? 

2.1  If you have operated the penetrations 1 without maintaining a nitrogen 
     pressure was any degradation of insulation resistance or anomolous 
     component operation detected? 

2.2  If no measurements were taken during periods when nitrogen pressure was
     not maintained, how were you assured that the insulation resistance was
     not degrading or degraded? 

2.3  How do you determine that circuit insulation resistances values are 
     satisfactorily maintained? 

3.0  Is there a need, as determined by either the vendor or yourself, to 
     maintain penetrations pressurized 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 
     10 days. In addition, provide an oral response by 4:00 p.m.(Local Time)
     November 25, 1977. Responses should be submitted to the Director of the
     appropriate NRC Regional Office. A copy of written responses should be 
     forwarded to the U. S. Nuclear Regulatory Commission, Office of 
     Inspection and Enforcement, Division of Reactor Operations 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. 



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