PG&E to replace transformer at Calif. nuclear plant

LOS ANGELES, Aug 21 (Reuters) - Pacific Gas & Electric Co has decided to replace rather than fix a main step-up transformer that caught fire earlier this week at its Diablo Canyon nuclear power plant in California, a company spokeswoman said on Thursday.

There is yet no schedule for the return of the 1,118-megawatt Unit 2 at the plant near San Luis Obispo, California, said Sharon Gavin, spokeswoman for the utility, which owns and operates the two-unit plant.

She said the company still expects the outage of the plant to be short-term, but would not elaborate.

She said a replacement transformer, valued at about $2 million, is on site. It will take the place of the damaged one as soon as the cause of a Sunday fire is determined, she said.

It will take several days to swap out the transformers, Gavin said.

The transformer caught fire on Sunday and caused the reactor to shut. Unit 1 of similar size at Diablo Canyon has remained in operation as Unit 2 has been out of service.

Each of the Diablo Canyon reactors has three main-bank transformers. Each transformer steps up voltage from 25,000 volts to 500,000 volts and onto the regional power grid, Gavin said.

The transformers are designed to last 40 years, but in practice the industry has noted that they last 20 to 30 years, Gavin said. The one that burned was 9 years old. The transformers each have a footprint of 12 feet by 20 feet and stand about 20 feet tall.

Unit 2 went into operation 22 years ago, and Unit 1 opened in 1985.

Diablo Canyon is about 200 miles northwest of Los Angeles and about 250 miles southeast of San Francisco. The utility PG&E is a unit of PG&E Corp (PCG.N: Quote, Profile, Research, Stock Buzz) based in San Francisco.

Diablo Canyon, when both units are in full operation, can supply enough electricity to serve about 3 million homes.

Diablo Canyon provides about 35 percent of PG&E's generation capacity of more than 6,200 megawatts. (Reporting by Bernie Woodall)