United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 78-02: Terminal Block Qualification

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

                             January 30, 1978  

                                                     IE Bulletin No. 78-02 

TERMINAL BLOCK QUALIFICATION 

Description of Circumstances: 

On January 18, 1978, Connecticut Yankee Atomic Company performed a screening
test intended to verify previous analyses of the environmental 
qualifications of unprotected terminal blocks used inside containment. The 
test was performed at the Franklin Institute Research Laboratories, 
Philadelphia, Pennsylvania. 

The test specimen was a Marathon M-6012 terminal block. It was exposed to a 
steam environment which was designed to envelope the calculated LOCA 
environmental conditions in the Haddam Neck containment. The pressure 
selected for the test was 40 psig for a period of 24 hours. 

The temperature profile consisted of a rise from an initial temperature of 
100 degrees Fahrenheit to 275 degrees Fahrenheit within ten seconds, 
followed by a steady state operation at 275 degrees Fahrenheit for four 
hours. This was followed by a drop of temperature to 140 degrees Fahrenheit 
within one hour, followed by a repetition of the initial temperature rise to 
275 degrees Fahrenheit (within ten seconds). The temperature then remained 
constant at 275 degrees Fahrenheit for the remaining 19 hours of the test 
period. 

During the initial screening test, 525 volts, single phase, 60 Hertz, ac 
voltage was applied to two pairs of terminals on the test specimen. 
Inability of the terminals to hold the voltage was defined before the test 
as an appropriate failure criterion. The test was initiated on January 19, 
1978. The terminal block functioned as intended during the first 5 hours of 
the test at which time one of the pairs of terminals failed the test. 

The cause of failure is still under investigation. The failure occurred 
during an operator error resulting in a pressure and temperature excursion 
which is outside the envelope of the intended test. Because of this, the 
licensee reran the test. 



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IE Bulletin No. 78-02                                    January 30, 1978 

The second screening test was initiated on January 25, 1978. This test 
included three test specimens: (1) an unprotected Marathon terminal block 
identical to the one used in the first test; (2) an unprotected Westinghouse
terminal block; and (3) a GE terminal block enclosed in a NEMA type 12 box 
identical to the ones in use in the Haddam Neck plant. The test specimens 
were exposed to an environment having temperature and pressure profiles 
essentially the same as those of the first test, minus the inadvertent 
overpressure transient. All the test specimens successfully operated through
the two temperature rise profiles in the test sequence. However, after 21 
hours in the test environment, the lower pair of terminals of the 
unprotected Marathon terminal block failed. The failed terminal points were 
disconnected and the test was completed. No further failures occurred. The 
failure mechaniSM of the terminal blocks during the first and second tests 
appears to be similar, i.e., the terminal pair that failed in each of the 
tests was the lower pair on the terminal block. Detailed analysis are in 
progress to identify the exact cause of failure. 

Actions to be Taken by Licensees and Permit Holders: 

For all power reactor facilities with an operating license or a construction
permit: 

(1)  Determine whether or not unprotected terminal blocks as used in your 
     facility in systems which must function in the post-accident 
     environment; 

(2)  If such terminal blocks are used, identify the systems involved and 
     provide the documentation which demonstrates that these terminal blocks
     have been environmentally qualified; and 

(3)  If documentation is not available, provide your plans and schedule for 
     achieving full qualification of affected circuits. 

     For holders of operating licenses, your response to this bulletin is 
     required to be in this office within 14 calendar days of the date of 
     issue of this bulletin. 

     For holders of construction permits, your response to this bulletin is 
     required to be mailed within 30 calendar days of the date of issue of 
     this bulletin. 



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IE Bulletin No. 78-02                                    January 30, 1978 

     Copies of your response are to be provided in the same time frame 
     directly to the Director, Office of Nuclear Reactor Regulation, and to 
     the Director of Reactor Operations Inspection, U.S. Nuclear Regulatory 
     Commission, 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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