United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 84-47: Environmental Qualification Tests of Electrical Terminal Blocks

                                                             SSINS NO: 6835 
                                                             IN 84-47      

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

                                June 15, 1984

Information Notice No. NO 84-47:    ENVIRONMENTAL QUALIFICATION TESTS OF 
                                   ELECTRICAL TERMINAL BLOCKS 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 

This information notice is being issued to provide licensees and 
construction permit holders with information pertaining to the results of a 
recent NRC-sponsored environmental qualification methodology research test 
conducted on electrical terminal blocks. This information notice also serves 
as an early notification regarding the reduction of insulation resistance 
values sustained by certain terminal blocks used in a Conax Electrical 
Penetration Assembly during a design basis event simulation test. 

It is expected that recipients will review the information for applicability
to their facilities. No specific action or response notice is required. 

Description of Circumstances: 

1.   Additional information on NRC-sponsored test on terminal blocks In 
     1981, the NRC sponsored a research test on-terminal blocks to 
     investigate the insulator deterioration of the terminal blocks under 
     accident conditions. This test was conducted at the Sandia National 
     Laboratories (SNL) in Albuquerque, New Mexico. The test results of this 
     earlier test program were published in Information Notice No. 82-03. 
     The results then indicated that the performance of the terminal blocks 
     was questionable, however, the results were inconclusive because there 
     were several areas where test conditions deviated from the actually 
     installed conditions. Recently, in order to quantify the performance of 
     realistically installed and protected terminal blocks in a LOCA 
     environment, SNL tested 24 more terminal blocks of different models 
     from four selected manufacturers. 

     Previous testing data on the terminal blocks indicated that neither the
     accelerated aging process nor the seismic testing will significantly 
     affect terminal block performance; therefore aging and seismic 
     simulation was not incorporated in the later SNL test. Terminal blocks 
     were tested in the "as received" condition to simulate normal handling 
     during installation. Additionally, no special care was taken during 
     test preparation to prevent the deposit of fingerprints or other 
     contaminants on the terminal block surfaces. 


8406130315 
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     Test terminal blocks were installed inside NEMA-4 electrical enclosures
     with 1/4" diameter weep holes in the bottom. Cables entered the boxes 
     from the side through "liquid tight" conduit. To simulate cables 
     entering through conduit from a cable tray system, the conduit was 
     terminated inside the test chamber and the conduit end was not sealed. 
     The test was divided into two phases; each phase was tested under 
     temperature profiles closely following the PWR temperature profile as 
     described in Appendix A of IEEE 323-1974. 

     Phase I consisted of an 11-day exposure to a steam-only environment, 
     and Phase II consisted of approximately one day of simultaneous 
     steam/chemical spray followed by a 5-day exposure to a steam 
     environment. Saturated steam conditions were maintained throughout both 
     test phases. Details of the test and test connections are being 
     documented in NUREG/CR-3418 which will soon be published by the NRC. 
     The terminal blocks were powered at voltages typical of in-plant 
     applications: 4 V dc typical of RTD circuits, 45 V dc typical of 
     instrumentation circuits, and 125 V dc typical of control circuits. The 
     terminal-to-terminal leakage currents were monitored during both Phase 
     I and Phase II tests, and the terminal-to-ground leakage currents were 
     monitored during the Phase II tests only. 

     The SNL test provides the following significant results: 

     (1)  the surface moisture film formed during the test reduced 
          insulation resistance to 10-2 to 10-5 ohms from initial values of 
          10-8 to 10-10 ohms; the reduction in insulation resistance 
          occurred during the steam exposure portion of the LOCA simulation, 

     (2)  at 45 V dc, leakage currents were on the order of 0.1 to 10 mA, 

     (3)  at 4 V dc, insulation resistance was at 5 x 10-3 to 7 x 10-4 ohms,
          and 

     (4)  one open failure was observed when leakage currents continued to 
          increase for a 90-minute period to values which caused a 12-AWG 
          wire to separate from the terminal point of the terminal block. 
          The separation occurred at the terminal block - wire junction of a 
          125 V dc circuit. 

2.   Low insulation resistance resulted during qualification testing of 
     terminal blocks used in low voltage instrumentation/control (I/C) 
     electrical penetration assembly (EPA) 

     In a Part 50.55(e) Potential Reportable Deficiency Report, the Arizona 
     Public Service Company (APS) has recently reported to the NRC that 
     during the review of a qualification test report on terminal blocks 
     used in low-voltage (I/C) EPA supplied by CONAX Corporation, APS has 
     observed that insulation resistance (IR) values between terminal points 
     of the terminal blocks were substantially reduced during simulation of 
     design basis events. APS concluded that the low-level signals (up to a 
     maximum 48 V dc and 4-20 mA range) cannot tolerate this low IR 
     condition. This 
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     condition could result in erroneous response in the sensing and control
     functions, which in turn might jeopardize reliable plant operation 
     during accident conditions. APS reported that the test terminal blocks 
     were made by Kulka Electric Corporation and that during an 
     investigative test, the terminal blocks also failed the "as-installed 
     conditions" test in transmitter and RTD circuits. APS further indicated 
     that Raychem splices are under consideration as replacement for the 
     terminal blocks for transmitter and RTD circuit applications at the 
     Palo Verde units. 

Discussion: 

This information notice highlights a potential concern that may exist when 
terminal blocks are exposed to a steam environment. 

The results of the SNL test show that a moisture film will form on the 
surface of the terminal block during the simulation of the LOCA/MSLB events,
and will result in the reduction of insulation resistance between terminal 
points and ground, and thus will allow some leakage currents to flow to 
ground. 

Based on the review of the SNL test and the review of other qualification 
test reports on terminal blocks, the NRC staff recognizes that leakage 
currents do exist during LOCA/MSLB simulations and that the leakage currents
may be of significance in some applications. Although no written response to
this notice is required, it is suggested that licensees and construction 
permit holders 1) review their facilities to determine if terminal blocks 
are used in low-voltage applications, such as in transmitter and RTD 
circuits, and 2) review terminal block qualification documents to ensure 
that the functional requirements and associated loop accuracy of circuits 
utilizing terminal block will not degrade to an unacceptable level due to 
the flow of leakage currents that might occur during design basis events. 
Instances where fuses were used to monitor leakage currents, and where 
failure criteria were based on the failure of these fuses (1 ampere or less) 
do not provide information about leakage currents of magnitude that are less 
than the fuse rating. Data provided under these instances are not considered 
to be acceptable data. The NRC staff considers this review to be part of the
on-going activities that the licensees are currently undertaking to resolve 
other environmental qualification deficiencies to meet the deadline and 
requirements set forth in the EQ final rule, 10 CFR 50.49. 

When supporting data for leakage currents are not substantiated during this 
review, one of the following possible corrective actions should be 
considered: 

     1)   Perform a valid qualification test of the installed terminal 
          blocks with provision for the continuous monitoring of leakage 
          currents throughout the test, and perform analysis to demonstrate 
          that acceptable loop accuracy and associated response time for 
          instrument circuit utilizing terminal block are being maintained           
          throughout various operating conditions. 
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     2)   Obtain documentation from valid qualification tests already 
          performed with substantiated data for leakage currents, and 
          perform appropriate analysis as stated in 1) above. 

     3)   Replace the installed terminal blocks with qualified splices. 

In addition to the concern of leakage currents being addressed in this 
notice, licensees and construction permit holders are reminded that other 
information concerning on-going preventive maintenance activities that 
involve periodic inspection of terminations and terminal blocks for 
cleanliness as described in the previously published information notice No. 
82-03 remains in effect. 

If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional office, or this office. 


                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  R. G. LaGrange, NRR
                    (301) 492-8208

                    N. B. Le, IE
                    (301) 492-9673

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