Headquarters Daily Report NOVEMBER 10, 1997 *************************************************************************** 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 IV NOV. 10, 1997 Licensee/Facility: Notification: Pacific Gas & Electric Co. MR Number: 4-97-0086 Diablo Canyon 1 2 Date: 11/10/97 Avila Beach,California Telephone Call from SRI Dockets: 50-275,50-323 PWR/W-4-LP,PWR/W-4-LP Subject: UNIT 2 STARTUP TRANSFORMER REPLACEMENT Discussion: Pacific Gas and Electric has implemented numerous long-term actions to improve the short circuit withstand capability of the Diablo Canyon startup transformers and to provide a means to cope with normal control of the 230 kV grid system (one of two sources of off-site power). As part of these actions, the licensee is replacing its startup transformers with improved, load tap changing transformers. The Unit 1 startup transformer was replaced during the last Unit 1 refueling outage earlier this year. On November 8, 1997, at 12:35 a.m. PST, the licensee commenced replacement of the Unit 2 startup transformer. This was done while Units 1 and 2 were at full power. The evolution required de-energizing startup power to both operating units, since 230 kV power feeds both unit startup transformers from a single line. This placed both units in a 72-hour shutdown action statement per Technical Specifications. Startup power was restored to both units at 7:29 a.m. (7 hours later), by feeding the Unit 2 startup bus from the Unit 1 startup transformer through the Unit 1/Unit 2 startup bus cross-tie breaker. Prior to the evolution, the licensee conducted simulator training for the operators for loss of off-site power, unit trip, and related scenarios. They also implemented other contingencies, such as maintaining all diesel generators operable and preventing any other maintenance or testing activities to be performed, while startup power was unavailable. Licensee operations managers were present in the control room throughout the evolution. Dismantling and removing the existing Unit 2 startup transformer and installing the new Unit 2 transformer will take about one week. During this time, the Unit 1 startup transformer will continue to provide startup power to Unit 2 through the cross-tie breaker. After the new Unit 2 startup transformer is in place, 230 kV power to both units will again have to be isolated. About 20 hours will be required to reconnect and test the new transformer. Regional Action: Several conference calls involving senior licensee, Region IV, and NRR management were conducted preceding the replacement activity. The calls provided an opportunity for the NRC and the licensee to discuss and clarify the contingency actions which were put in place for the evolution. Resident and Region-based inspectors provided continual coverage of the evolution until Unit 2 startup power was restored through Unit 1. REGION IV MORNING REPORT PAGE 2 NOV. 10, 1997 MR Number: 4-97-0086 (cont.) Contact: David Proulx (805)595-2354 Howard Wong (510)975-0296 _