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Information Notice No. 83-42: Reactor Mode Switch Malfunctions
SSINS No.: 6835 IN 83-42 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 June 23, 1983 Information Notice No. 83-42: REACTOR MODE SWITCH MALFUNCTIONS Addressees: All boiling water reactors holding an operating license (OL) or construction permit (CP) Purpose: This information notice is provided as an early notification of potentially significant events concerning mode switch malfunctions while changing operating modes. It is expected that recipients will review the information for applicability to their stations. No specific action or response is required at this time. Description of Circumstances: Susquehanna 1 Events: On March 22, 1983, Susquehanna Unit 1 was being prepared for a startup with all control rods fully inserted. The reactor mode switch was placed in the startup position in order to perform a surveillance test. Following the completion of the surveillance test the mode switch was returned to the shutdown. position which design produces a full scram signal. However, this time, the reactor protection system (RPS) channel "B" failed to actuate, and only a half scram signal was produced. The operator verified that all control rods remained fully inserted, and the operator depressed the reactor scram buttons as a precautionary measure. The manual scram actuated both channels of the RPS. The mode switch was test cycled several times and proper operation was intermittent. The switch was removed and a replacement mode switch was acquired from the NSSS supplier. Testing showed that there was improper contact continuity and this replacement switch was also deemed unacceptable. Four additional mode switches were acquired and all four mode switches successfully passed a bench test. One was used as a replacement. On May 16, 1983, Susquehanna Unit 1 was again being prepared for a startup. The reactor mode Switch was placed in the refuel position and immediately a scram signal and a group 1 isolation signal were generated. When the mode switch was placed in the startup position, the signals for a scram and a group 1 isolation were again produced. The reactor mode switch was a recently installed modified version of the type used in the March 22 event. The startup was, suspended until an acceptable replacement could be obtained. 8305110479 . IN 83-42 June 23, 1983 Page 2 of 3 Dresden 2 Event: On December 17, 1982, power at Dresden Unit 2 was being decreased to a hot standby condition so that a crack could be repaired in an emergency drain line of a feedwater heater. When the reactor power was less than one percent the reactor mode switch was moved from the run position to the startup position. With the mode switch in the startup position, the group 1 isolation signal from low main steam line pressure (850 psig) should be bypassed. When the reactor pressure decreased to less than 850 psig a group 1 isolation occurred. The closure of the main steam line isolation valves resulted in a reactor scram. Similar events had previously been experienced at Dresden Unit 2 and at Quad Cities Unit I. All had resulted in group 1 isolations from a low main steam line pressure signal after the mode switch was placed in a position that normally bypasses this signal. Discussion: Following the March 22 event at Susquehanna, Pennsylvania Power and Light contacted a research laboratory to test the failed reactor mode switch. The test consisted of a verification of contact positioning during both smooth and uneven switch rotation. Upon completion of the testing for contact positioning the reactor mode switch was disassembled so that the individual parts could be examined. The test results revealed numerous contact positioning errors that appear to be the result of significant irregularities in the mode switch cam shaft parts and large design clearances resulting in imprecise operation of the cam followers. General Electric was contacted and confirmed that problems existed with the mode switch used at Susquehanna General Electric identified this mode switch by the model name RUDEL-GOULD, manufactured by Gould for General Electric. Currently Susquehanna is the only operating station that uses this type of switch. General Electric intends to issue a Field Disposition Instruction (FDI) to alert other potential users of this switch about its problems and required modifications. The mode switch that was in place at Susquehanna on May 16 was a newly modified mode switch. General Electric inspected the modified mode switch and found a switch shaft cam improperly oriented and cam surface irregularities. This mode switch was temporarily replaced with a switch that was successfully tested following the March 23 event. The reactor mode switches that failed at Dresden Unit 2 and Quad Cities Unit are identified by the model number SB-1 and are commonly used on BWR 2s through BWR 5s. It appears that because of years of service the SB-1 switch has sticking contacts. Both stations replaced the mode switch during the last refueling outage. BWR owners should be unexplained isolation or scram signals that may have coincide with mode switch movement while changing operating states. It may be prudent for licensees to change their manual scram procedures to require the use of the scram push buttons before moving the mode switch to the shutdown position. . IN 83-42 June 23, 1983 Page 3 of 3 No written response to this notice is required. 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: Paul R. Farron, IE (301) 492-4766 Attachment: 1. List of Recently Issued IE Information Notices .
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