Diablo Canyon not as vulnerable to tsunamis as Japan's nuclear plants, PG&E says

dsneed@thetribunenews.comMarch 14, 2011 

Diablo Canyon nuclear power plant has several wells to provide water to cool the reactor in an emergency.

PHOTO COURTESY OF PG&E

Diablo Canyon nuclear power plant has several design features that are intended to prevent the kind of crisis facing nuclear power plants in Japan following Friday’s devastating earthquake and tsunamis.

In one reactor at the Fukushima Dai-ichi plant, cooling water was lost, forcing workers to use fire hoses to pump seawater into the reactor to prevent a core meltdown. Meltdowns such as what took place at the Chernobyl power station in the former Soviet Union have the potential to release large amounts of radiation into the environment.

A main priority is keeping large pumps operating that circulate cooling water within the reactor. If power is lost, Diablo Canyon — owned by PG&E — is equipped with diesel generators that can run the pumps. These are maintained and tested on a regular basis, said Kory Raftery, Diablo Canyon spokesman.

Diablo Canyon also has several sources of fresh water that can be used to replenish cooling water in the reactors, if it is lost. Using seawater as cooling water is a last resort because it is corrosive to the reactor core.

The main source of freshwater at Diablo Canyon is a desalination plant that turns ocean water into fresh water. Water is stored in pools on a hill behind the plant that could inject water into the reactor using gravity.

The property surrounding Diablo Canyon also has several wells that could supply water in an emergency, Raftery said. These sources of water can also be used to replenish water in the plant’s two spent-fuel storage pools, if needed.

Diablo Canyon is considered much less vulnerable to a tsunami than reactors in Japan that sit on low-lying coastal plains. Diablo Canyon sits atop a coastal bluff, 85 feet above sea level.

The cooling water intake structures that draw ocean water into the plant to condense steam after it has passed through the electrical turbines are surrounded by breakwater that are designed to provide protection from large waves.

Although earthquakes are Diablo Canyon’s main safety concern, seismologists do not believe that faults around the plant are capable of producing the kind of massive 9.0 magnitude quake that struck Japan.

Diablo Canyon is designed to withstand a 7.5 magnitude quake. Extensive studies done by seismologists with plant owners PG&E, the Nuclear Regulatory Commission and the U.S. Geological Survey show that four earthquake faults in the vicinity of the plant could produce quakes of no more than 6.5 magnitude.

The main difference is that faults around Diablo Canyon are strike/slip faults in which tectonic plates slide horizontally past one another. The faults along Japan’s coastline are subduction faults, in which one plate slides beneath another, Raftery said.

Seismologists say subduction faults are capable of delivering more powerful jolts than strike/slip faults and are more likely to displace ocean water, causing tsunamis.

As required by the federal Nuclear Regulatory Commission, emergency response drills are conducted regularly at the Diablo Canyon to practice dealing with the effects of earthquakes and tsunamis. Numerous state and local agencies participate in these drills.

Reach David Sneed at 781-7930.

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