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 . 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. . 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. 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