Seismic study near California nuclear plant wins key approval

* Four fault lines run near nuclear power plant

* Sonar could harm animals in protected wildlife areas

* Plant operator PG&E still needs federal, other approvals

By John Upton

SACRAMENTO, Calif., Aug 20 (Reuters) - A plan to fire powerful sonar devices and map seismic fault lines off California's central coast near a nuclear power plant received key approval on Monday from state officials despite concerns about its impact on marine life.

The proposed $64 million seismic study was designed to help Pacific Gas & Electric (PG&E) and its regulators gauge hazards posed by potential earthquakes near the 2,160-megawatt Diablo Canyon power plant in San Luis Obispo County, about 183 miles (294 km) northwest of Los Angeles.

The tests are needed to ensure that the waterfront facility is capable of withstanding an earthquake along one or more of four nearby fault lines. One of the faults was discovered in 2008 and is not well understood, while others were mapped using outdated technology.

The study had been planned since 2006 but gained a sense of urgency after an earthquake and tsunami off the coast of Japan in March 2011 triggered a nuclear meltdown at the Fukushima Daiichi power plant.

Following the Fukushima meltdown, PG&E began fast-tracking the seismic study and agreed to delay pursuing federal relicensing of the 27-year-old power plant until the seismic study is complete.

Operating permits issued by the U.S. Nuclear Regulatory Commission for Diablo Canyon's dual waterfront reactors, which produce about 10 percent of California's power needs, are due to expire in 2024 and 2025.

Fierce debate over the proposed study has coincided with an extended shutdown of the only other nuclear power plant operating in California. The San Onofre plant was taken offline in January following a radioactive leak and remains shuttered by its operator, Southern California Edison, a unit of Edison International.

The sonar tests will help paint a detailed three-dimensional picture of the seismic fault lines in the area. But they are controversial because the piercing, around-the-clock underwater sounds could harm animals in protected wildlife areas and limit commercial fishing.

CONDITIONS ON TESTING

The California State Lands Commission voted to allow the tests to move forward but imposed a raft of conditions, including restricting the firing of sonar guns and hydrophones to certain areas and certain months.

"I'm not going to tell you that we won't have some impacts," PG&E government affairs official Mark Krausse told the commissioners on Monday. "Our focus has been on minimizing the impacts from this work."

Commission Chairman Alan Gordon said the commissioners were forced to weigh unavoidable impacts of the study with the risks of an accident.

"The consequences of a nuclear accident at this site make it absolutely imperative and time sensitive that we get the information that these studies will provide," Gordon said during the hearing.

PG&E still needs to secure approval of federal and some other state agencies before it can proceed but it hopes to complete the study this winter.