NRC and Diablo Canyon Prepare for Fukushima-like crisis

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Diablo Canyon Power Plant is an electricity-generating nuclear power plant at Avila Beach in San Luis Obispo County, California. The plant has two Westinghouse-designed 4-loop pressurized-waternuclear reactors operated by Pacific Gas & Electric.

The facility is located on about 750 acres (300 ha) in Avila Beach, California.   It was built directly over a geological fault line, and is located near a second fault.

Pacific Gas & Electric Company went through six years of hearings, referenda and litigation to have the Diablo Canyon plant approved. A principal concern about the plant is whether it can be sufficiently earthquake-proof. The site was deemed safe when construction started in 1968.

However, by the time of the plant’s completion in 1973, a seismic fault, the Hosgri fault, had been discovered several miles offshore. This fault had a 7.1 magnitude quake 10 miles offshore on November 4, 1927, and thus was capable of generating forces equivalent to approximately 1/16 of those felt in the 1906 San Francisco earthquake.

In September 1981, PG&E discovered that a single set of blueprints was used for these structural supports; workers were supposed to have reversed the plans when switching to the second reactor, but did not.

According to Charles Perrow, the result of the error was that “many parts were needlessly reinforced, while others, which should have been strengthened, were left untouched.”


Nonetheless, on March 19, 1982 the Nuclear Regulatory Commission decided not to review its 1978 decision approving the plant’s safety, despite these and other design errors.

For 18 months, operators at the Diablo Canyon nuclear plant near San Luis Obispo didn’t realize that a system to pump water into one of their reactors during an emergency wasn’t working.

It had been accidentally disabled by the plant’s own engineers, according to a report issued in March on the safety of nuclear reactors in the United States.

The problem at Diablo Canyon, which is owned by Pacific Gas and Electric Co., involved a series of valves that allow water to pour into one of the plant’s two reactors during emergencies, keeping the reactor from overheating.

The plant draws cooling water from the Pacific Ocean, and during heavy storms both units are throttled back by 80 percent to prevent kelpfrom entering the cooling water intake. The cooling water is used once and is not recirculated but rather returned to the Pacific Ocean at higher temperature.

In June, the utility and the Nuclear Regulatory Commission both realized that business as usual would not be a way of life after Fukushima, and the relicensing request was suspended, pending completion of the seismic studies. Now, December 2015 is the earliest Diablo Canyon could be relicensed.

Similarly, the state Public Utilities Commission has closed a request by PG&E to recoup $85 million from ratepayers to pay for relicensing.

“We can now focus on making sure the seismic studies are well designed and independently peer-reviewed at every step of the way,” said Rochelle Becker of the Alliance for Nuclear Responsibility, which urged the Public Utilities Commission to close the request rather than just suspend it.

PG&E has finished two of three years of intense seismic fieldwork focusing on the four major faults around the plant — the Hosgri, Shoreline, San Luis Bay and Los Osos faults. Two-dimensional onshore and offshore surveys have been completed.

The agency maintains that a similar event in the United States is highly unlikely and all plants, including Diablo Canyon, are designed to withstand the type of earthquakes nearby faults are likely to produce.The nuclear industry has determined that the tsunami, not the earthquake itself, was responsible for most of the damage sustained by the Fukushima plant. Specifically, the tsunami inundated the plant’s backup safety equipment, leaving the facility without power.

See the Diablo Canyon Timeline Here

Source: SF Gate

Source: San Luis Obispo

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