Headquarters Daily Report SEPTEMBER 09, 1998 *************************************************************************** REPORT NEGATIVE NO INPUT ATTACHED INPUT RECEIVED RECEIVED HEADQUARTERS û REGION I û REGION II û REGION III û REGION IV û PRIORITY ATTENTION REQUIRED MORNING REPORT - HEADQUARTERS SEP. 09, 1998 Licensee/Facility: Notification: Consolidated Edison Co. Of New York MR Number: H-98-0138 Indian Point Unit No. 2 Date: 09/09/98 Subject: 10 CFR PART 21 - STICKING INERTIAL LATCH IN WESTINGHOUSE MODEL DB-50 CIRCUIT BREAKER Discussion: On 8/11/98, during a surveillance test of auxiliary feedwater (AFW) pump "21" at Indian Point 2 (IP2), the pump failed to start on demand (Event Notification #34631, 8/12/98). The cause of the pump failure was the supply circuit breaker (Westinghouse Model DB-50) failing to close when the operator turned the control switch. Investigation by the licensee determined that the inertial latch attached to the circuit breaker operating mechanism was holding the cross bar in the open position, preventing the breaker from closing. The latch is designed to momentarily catch the cross bar when the breaker opens to prevent the bar from bouncing back and allowing the arcing contacts to touch. Once the breaker cross bar movement subsides after opening, the latch is supposed to release the cross bar so that the breaker is ready to be closed on the next demand. The licensee contracted an independent laboratory to perform a root cause analysis on the failed breaker. The contractor determined that the cause of the sticking latch was spalling of the plating used on the latch and its pivot pin, as evidenced by small particles of plating material found on the pin when the inertial latch assembly was disassembled (10 CFR Part 21 report - Event Notification #34713, 8/29/98). The particles caused high frictional forces between the latch and the pivot pin, preventing the latch from returning to its normal position. Subsequent discussion with Westinghouse Repair & Replacement Services (RRS) indicated that Westinghouse had not heard of this particular problem before, but RRS agreed to review the operating mechanism assembly process for any possible contributing factors. During the operating mechanism assembly process the pivot pin is measured to ensure it is within tolerance before attaching it to the operating mechanism frame. After brazing the pin to the frame, the entire assembly is plated with a zinc material by dipping the assembly in a gold dichromate solution followed by a plating process. The inertial latch is also plated. Following the plating process, both the pin and the hole in the inertial latch are polished with emory cloth and cleaned to remove any excess plating material. During final assembly a small amount of molybdenum disulfide powder suspended in isopropyl alcohol is applied to the pivot pin to ensure the latch moves freely, and a snap ring is installed on the end of the pivot pin to hold the latch in place. The operating mechanism is then installed in a test breaker and cycled several times to ensure proper operation before shipping. Westinghouse reviewed the assembly process and decided that, even though no other cases of a sticking inertial latch have been reported, the process should be changed to preclude potential problems. Westinghouse issued a letter to the shop floor instructing workers to remove the plating from any inertial latches and pivot pins currently in stock. The HEADQUARTERS MORNING REPORT PAGE 2 SEP. 09, 1998 MR Number: H-98-0138 (cont.) assembly process procedure will be changed to instruct workers to mask off the inertial latch and pivot pin during the plating process. Westinghouse Nuclear Services Division plans to issue a Nuclear Service Advisory Letter to alert customers to the potential problem. The letter will recommend that customers inspect the inertial latch for freedom of movement during the next scheduled preventive maintenance. Contacts: D. Skeen, PECB/DRPM (301) 415-1174 E-mail: dls@nrc.gov K. Naidu, HQMB/DRCH (301) 415-2980 E-mail: krn@nrc.gov _