Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 85-98
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
December 26, 1985
Information Notice No. 85-98: MISSING JUMPERS FROM WESTINGHOUSE REACTOR
PROTECTION SYSTEM CARDS FOR THE
OVER-POWER DELTA TEMPERATURE TRIP
FUNCTION
Addressees:
All Westinghouse-designed pressurized water reactor facilities holding an
operating license (OL) or a construction permit (CP).
Purpose:
This notice is provided to alert licensees to recent discoveries of missing
configuration jumpers from over-power delta temperature (OPDT) reactor trip
function cards at Westinghouse reactors. It is expected that recipients will
review this information for applicability to their facilities and consider
actions, if appropriate, to preclude similar problems at their facilities.
However, the suggestions contained in this notice do not constitute NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances:
Following a reactor trip at McGuire Unit 2 on November 24, 1984, an engine
reviewed the time plots of the OPDT channel setpoints during an
investigation of another matter. He noticed spikes on two of the four
channels, coincident with the reactor trip. Although the spikes looked
similar to post-trip electrical power spikes, they were in the opposite
direction from what was expected and did not occur on all channels. On
November 26, further investigation of these spikes with the process control
system vendor (Westinghouse) revealed that these channels were responding
improperly because an electrical jumper was missing from their function
cards in the 7300 cabinet. The purpose of the jumpers is to limit the lead
circuit response so that it will not raise the trip setpoint under
conditions of decreasing average temperature (T-ave). This circuit is
designed to compensate for the lag caused by reactor coolant flow time and
temperature instrument response time under conditions of increasing T-ave.
Under conditions of decreasing T-ave, the same circuit will raise the
setpoint unless the jumpers are installed.
Review of previous test data indicated that the jumpers were removed during
a preoperational test to perform a negative step response function check.
The jumpers were apparently not reinstalled on two of the cards following
the test. The licensee has attributed this error to deficient vendor
drawings and documents, which did not contain explicit guidance regarding
the need for the missing jumpers.
8512230041
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IN 85-98
December 26, 1985
Page 2 of 3
Westinghouse personnel at the McGuire Station informed Westinghouse
personnel at the V. C. Summer Station of the problem in December 1984.
Despite the notification, the absence of the jumpers was not detected by
visual inspection of the equipment at the Summer Station. However, during a
post-trip review on August 28, 1985, a shift technical advisor discovered
that all three OPDT channels exhibited nonconservative behavior under
conditions of decreasing T-ave. Investigation revealed that the three cards
at the Summer Station were missing the same jumpers that had been missing
from the McGuire cards.
Further investigation at the Summer Station indicated that the jumpers had
been missing since the initial plant startup in October 1982. The McGuire
cards were modified after initial startup, and it is not known whether the
original configuration also contained the same error. The preoperational
testing,and subsequent surveillance testing at both plants failed to detect
the misconfigurations because none of the tests included test signals that
simulate conditions of decreasing T-ave.
Discussion:
The OPDT trip is designed to protect against fuel rod cladding failure
caused by excessive power density. It also limits the required range of
protection from the over temperature delta temperature (OTDT) trip circuit
and provides a backup to the high neutron flux trip. Analyses for the
McGuire plant indicate the OPDT trip will be the first reactor trip signal
for some small steam line breaks (0.4 to 0.8 ft2) outside containment with
the reactor at power. However, both licensees have concluded that operation
without the OPDT trip could not result in the violation of any safety limits
because of the protection provided by the OTDT, high flux and pressurizer
low pressure trips.
The OPDT set point is calculated according to the following formula:
where: T = the measured T by RTD manifold
instrumentation
= the function generated by the rate-lag controller
for the T-ave dynamic compensation
K5 = 0.02/degree F for increasing T-ave
= 0/degree F for decreasing T-ave
The lead/lag circuit cards used by Westinghouse in the OPDT circuits are
used for many different functions. They can be configured for bipolar output
(-10 volts to +10 volts) or unipolar output (-0.7 volts to +10 volts). The
uni-polar configuration is achieved by hardwiring a diode in the output to
limit the negative voltage to -0.7 volts. This is sufficiently close to zero
for most unipolar applications, but not for the OPDT function. To achieve an
output range of exactly 0 to +10 volts, a low-limiting (JA) jumper must be
installed to feed any negative voltages back through an operational
amplifier to ensure that the output cannot go negative. This, in effect,
sets K5 exactly equal to zero for decreasing T-ave.
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IN 85-98
December 26, 1985
Page 3 of 3
It is typical for Westinghouse personnel, under contract to the licensee, to
initially configure, install, and perform testing of the trip function
cards. Modifications, maintenance and surveillance testing are typically
performed by licensee personnel. In all cases, it is ultimately the
responsibility of the licensee to ensure that the cards are configured
properly. The necessary information for configuring the cards is contained
in the precautions, limitations and setpoints document and the scaling
manual for the card. However, the procedures used by Westinghouse personnel
failed to identify the problem during card configuration verification or
preoperational testing at the Summer Station. Surveillance tests, which are
typically derived from vendor test procedures, also failed to identify the
problem.
Technical Specifications require the derivative input from T-ave to produce
a specific setpoint response for positive derivatives and no response for
negative derivatives. The calibration of the positive rate response is
normally included in surveillance test procedures, but the verification of
zero response to negative rates has typically not been included, on the
rationale that no calibration is required for a zero response. However, the
inability of the Summer Station to visually verify the proper card configur-
ation demonstrates the value of an actual test of the circuit configuration.
No specific action or written response is required by this information
notice. 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: Steven M. Long, IE
(301) 492-7159
Attachments: List of Recently Issued IE Information Notices
