Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
May 24, 1993
NRC INFORMATION NOTICE 93-38: INADEQUATE TESTING OF ENGINEERED
SAFETY FEATURES ACTUATION SYSTEMS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to situations in which inadequate testing of
engineered safety features actuation systems was performed. It is expected
that recipients will review the information for applicability to their
facilities and consider actions, as appropriate, to avoid similar problems.
However, suggestions contained in this information notice are not NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances
South Texas Units 1 and 2
On September 15, 1992, personnel at the South Texas Nuclear Plant
(South Texas) determined that a portion of the containment spray channels
between the process instrumentation and the actuation and logic circuitry was
not being tested. The containment spray system is an engineered safety
feature (ESF) and is required by technical specifications to be verified
operable for plant operation.
The controlling logic for the containment spray system is part of the
engineered safety features actuation system (ESFAS). The purpose of the ESFAS
is to sense plant conditions and, if required, transmit signals to actuate ESF
equipment to mitigate the consequences of postulated accidents. During plant
operation, a set of overlapping tests verifies that the ESFAS circuitry is
operable. These tests are performed from the point at which process
conditions are sensed through the signal output of the logic relays. When the
containment spray portion of the system is tested, the contacts for the logic
relays are opened to prevent inadvertent actuation of the containment spray
system. After testing of the containment spray logic is complete, the
contacts for the logic relays are returned to the normal closed position.
However, the test procedure does not require the test personnel to verify that
the contacts are closed and that the circuits are continuous. The licensee
has determined that a failure of these contacts to close could render the
circuitry inoperable.
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May 24, 1993
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For most of the circuits in the ESFAS, the bistables are normally energized.
The status of these circuits can readily be monitored and displayed on a
bistable status monitoring panel. However, to prevent spurious actuation of
containment spray, the bistables for the containment spray circuits are
normally deenergized and the status of the circuits cannot be monitored in the
same manner as the normally energized circuits. At South Texas, a test
circuit was provided in the containment spray circuitry to allow verification
of circuit continuity between the process instrumentation and the ESF
actuation and logic circuitry without actuating the containment spray system.
The test personnel were not aware that it was necessary to use this test
circuit to verify circuit continuity after closing the contacts.
After making the above discovery, the licensee tested the containment spray
circuitry and found the circuits acceptable. The licensee revised the
applicable procedures to ensure that these circuits would be tested during
future surveillances.
McGuire Units 1 and 2
On February 16, 1993, personnel at the William B. McGuire Nuclear Station
(McGuire) Units 1 and 2, determined that, similar to the event at South Texas,
continuity checks were not performed for the containment spray logic relay
contacts and for a contact in the reactor protection circuitry that was also
opened during testing. The contact in the reactor protection circuitry was
the channel test relay contact at the bistable output to the solid-state
protection system for containment spray. The licensee revised the applicable
procedures to ensure that these contacts would be tested during future tests.
Catawba Units 1 and 2
On February 16, 1993, personnel at the Catawba Nuclear Station Units 1 and 2,
determined that, similar to the condition at McGuire, continuity checks were
not performed for certain normally deenergized contacts. The licensee
verified the continuity of the circuits and revised procedures to ensure that
the contacts would be tested during future tests. In addition, the licensee
found that, for three channels in Unit 1 and two channels in Unit 2, the test
points on the printed circuit cards were mislabeled.
Byron Units 1 and 2
On February 22, 1993, personnel at the Byron Nuclear Power Station (Byron)
Unit 1, found a wiring discrepancy in a cabinet of the solid-state protection
system. The licensee determined that a test connection for containment
isolation phase B (set to actuate at 50 percent of the design pressure of the
containment) was wired to pin 5 of a terminal board instead of pin 6. Because
of this error, surveillance tests performed to verify that the containment
isolation phase B logic cicuitry was acceptable were actually performed on the
containment spray logic circuitry. As a consequence, surveillance tests of
the containment isolation phase B logic had not been performed as required.
This condition was later found to exist also in Unit 2. The licensee
consulted with the supplier, Westinghouse Electric Company, and corrected the.
IN 93-38
May 24, 1993
Page 3 of 3
discrepancy. Later, this condition was also found in the same test circuits
at the Braidwood Nuclear Power Station (Braidwood) and at McGuire.
Discussion
In three of the events described above, the testing of normally energized
ESFAS circuits was found to be inadequate because the licensee did not verify
that the contacts which were opened for the test were closed and the circuits
continuous after completing the test. Failure to close these contacts could
result in the failure of ESF equipment to actuate as required. Because
indication of continuity for this type of circuit may not be available in the
same manner as for normally energized circuits, other methods may be used to
verify that the contacts are closed and that the circuits are continuous.
Although these three events occurred at pressurized water reactors, the
potential exists for similar conditions at boiling water reactors.
The wiring discrepancy found in the test circuitry at Byron, Braidwood and
McGuire may also exist in test circuits supplied by Westinghouse at other
sites. At these three facilities, the discrepancy resulted in a failure by
the licensee to perform a required technical specification surveillance test
of the containment isolation phase B logic.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
ORIGINAL SIGNED BY
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact: P. Kim VanDoorn, RII
(704) 875-1681
Attachment:
List of Recently Issued NRC Information Notices.
