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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