United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-98: Missing Jumpers from Westinghouse Reactor Protection System Cards for the Over-Power Delta Temperature Trip Function

                                                        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 
Page Last Reviewed/Updated Tuesday, November 12, 2013