Headquarters Daily Report NOVEMBER 29, 1995 *************************************************************************** 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 - REGION II NOV. 29, 1995 Licensee/Facility: Notification: Tennessee Valley Authority MR Number: 2-95-0100 Sequoyah 1 Date: 11/29/95 Soddy-Daisy,Tennessee Dockets: 50-327 PWR/W-4-LP Subject: MAIN GENERATOR EXCITER ARCING; UPDATE TO EVENT NUMBER 29645 - ISSUED ON NOVEMBER 27, 1995 Discussion: This morning report is an update to Event Number 29645, issued on November 27, 1995, for the Sequoyah Nuclear Plant. In summary, Unit 1 was operating at 100% power, when the licensee started to reduce reactor power due to balance-of-plant process parameter indication swings from arcing on the generator exciter. The turbine was taken off-line, and reactor power was reduced to and maintained at 1 percent in Mode 2. Based on the potential degradation of plant safety, the licensee declared an Unusual Event, which was terminated nineteen minutes later when the exciter field breaker was opened and indication swings ceased. The licensee determined that numerous instrument loops became erratic/noisy, affecting safety related and non-safety related instruments. The instrument loops immediately stabilized when the generator was taken off-line. Examples of affected instruments included the #3 Cold Leg Accumulator level and pressure indication, and the Main Feedwater Pump Turbine "A" and "B" pressure, flow, and vibration. Some equipment began to be affected, which the licensee is still reviewing. The preliminary cause of the arcing on the Unit 1 generator exciter was determined to be worn electrical cable insulation on a lead from the permanent magnet generator to a resistor bank, located inside the exciter cabinet. The licensee has preliminarily concluded that the arcing resulted in the generation of electromagnetic interference, which affected various instruments. The licensee is continuing the investigation, and will evaluate the exciter and voltage regulator for damage. In addition, the licensee is evaluating the overall plant response. Regional Action: A Region based inspector was in the control room during the initial stages of the event. The resident inspectors are reviewing the licensee's activities. Contact: Scott Sparks (404)331-5619 _ REGION IV MORNING REPORT PAGE 2 NOVEMBER 29, 1995 Licensee/Facility: Notification: Arizona Public Service Co. MR Number: 4-95-0152 Palo Verde 3 Date: 11/29/95 Wintersburg,Arizona Telephone Call from Resident Insp. Dockets: 50-530 PWR/CE80 Subject: CRITICALITY FOLLOWING REFUELING OUTAGE Discussion: At 1:54 a.m. on November 28, 1995, Palo Verde Unit 3 returned to critical operations following the fifth refueling outage. The refueling outage began on October 14, 1995. Major work during the outage included extensive eddy current inspection of the steam generators and modifications to increase the recirculation ratio of the steam generators. Regional Action: The resident inspectors are following the licensee's actions to return Unit 3 to full power operation. Contact: R. Huey (510)975-0342 K. Johnston (602)386-3638 _ REGION IV MORNING REPORT PAGE 3 NOVEMBER 29, 1995 Licensee/Facility: Notification: Southern California Edison & San MR Number: 4-95-0153 Diego Gas & Electric Co. Date: 11/29/95 San Onofre 2 Senior Resident Inspector San Clemente,California Dockets: 50-361 PWR/CE Subject: PLANT SHUTDOWN TO INVESTIGATE SUSPECTED REACTOR COOLANT PUMP STATOR COOLING WATER LEAK Discussion: On November 28, 1995, at 11:42 p.m. (PST), San Onofre Unit 2 initiated a plant shutdown to investigate a suspected component cooling water leak on the stator cooling water jacket for Reactor Coolant Pump 2P002. The suspected leak was based on a computer alarm which indicated that a moisture sensor for Pump 2P002 had activated. The licensee made an initial containment entry at power to inspect the moisture sensor relay, located outside of the bioshield, and confirmed a valid signal from the sensor, located in a catch tray underneath of the reactor coolant pump. As of 8 a.m. (PST), on November 29, the plant was in Mode 3 and the licensee had entered containment to inspect the reactor coolant pump to determine the exact cause of the activation of the moisture sensor. The full scope of required actions will be determined upon completion of the pump inspection. Regional Action: The residents will monitor the licensee's actions. Contact: R. Huey (510)975-0342 J. Sloan (714)492-2641 _ REGION IV MORNING REPORT PAGE 4 NOVEMBER 29, 1995 Licensee/Facility: Notification: Pacific Gas & Electric Co. MR Number: 4-95-0154 Diablo Canyon 1 Date: 11/29/95 Avila Beach,California Call from Senior Resident Inspector Dockets: 50-275 PWR/W-4-LP Subject: UNIT 1 MANUAL TRIP Reportable Event Number: 29652 Discussion: At 10:15 p.m. (PST), on November 28, 1995, while Unit 1 was at 50 percent power, operators manually tripped the Unit 1 reactor in anticipation of an automatic trip due to the loss of the operating main feedwater pump (Pump 1-2). Unit 1 was starting up following a refueling outage and the other main feedwater pump (Pump 1-1) was out of service due to work on a check valve in the steam line to the pump turbine. The loss of the operating main feedwater pump was due to a failure of both speed probes. The failure of the speed probes resulted in a zero speed signal and the feedwater pump control system reacted by further opening the turbine governor valves. This caused the main feedwater pump to overspeed and resulted in an overspeed trip. The licensee is investigating to determine the cause of the speed probe failures, and whether both speed probes had failed simultaneously or one had failed earlier with the remaining speed probe failing at this point in time. Safety systems operated as designed with the auxiliary feedwater and steam dump control systems maintaining reactor core cooling. On the transfer of power to the 4 kV vital buses from the unit auxiliary transformer to the startup transformer, there was a start of Emergency Diesel Generator 1-1 (EDG 1-1). This was caused by a transient low voltage condition on the transfer of the 4 kV loads from the auxiliary transformer to the startup transformer. EDG 1-1 did not load onto the bus because the bus voltage had increased sufficiently on the transfer to the startup transformer. The start of EDG 1-1 has occurred previously as a result of reactor trips and had been evaluated to be in accordance with the electrical system design. Regional Action: The resident inspectors will monitor the licensee's investigation for the cause of the speed probe failures. Contact: H. Wong (510)975-0296 J. Dixon-Herrity (805)595-2353 _