Japan quake ignites Diablo nuclear concerns
March 18, 2011
In the aftermath of Japan’s nuclear calamity, concerns about Diablo Canyon nuclear power plant’s ability to withstand an earthquake and media reports that safety plans do not include earthquake procedures have the public demanding answers.
Even before last weeks earthquake and tsunami in Japan, PG&E’s application to extend its operating permit was controversial. The California Public Utilities Commission(PUC) directed the utility to do further seismic testing as part of its license renewal.
PG&E officials said the advanced seismic studies would be completed in 2013. Even so, they had asked for an April review hearing.
Early on Friday, the PUC announced they had postponed the April hearing so that it would have time to review safety lessons learned from the earthquake and tsunami in Japan.
Diablo’s seismic history
When the plant was first permitted in 1967, it was not required to have an earthquake emergency response plan. However, since then two faults have been discovered near the plant prompting earthquake procedures to be put in place.
Before the plant was put into operation, after the discovery of the Hosgri Fault in 1971 by Shell Oil, a long and contentious battle between the state and PG&E ensued raising the cost of construction, first estimated at $320 million, by over $5 billion. PG&E was also directed to hire geologists and seismologists to work in the plant’s geosciences department. As a result of finding the Hosgri Fault, Diablo’s design was changed and the plant was retrofitted to withstand a magnitude 7.5 earthquake.
In 1985, the $5.7 billion plant began producing energy.
In 2008, a second fault dubbed the Shoreline Fault was discovered less than a mile from the plant by U.S. Geological Survey (USGS) geologist Jeanne Hardebeck using data from USGS and PG&E monitors.
Even though the Nuclear Regulatory Commission concluded that Diablo Canyon’s design would withstand a potential earthquake on the Shoreline Fault, “The fault’s major characteristics are largely unknown, e.g., its length, proximity to the plant and relationship to the Hosgri Fault (whether an earthquake beginning on the Hosgri Fault could continue on the Shoreline Fault, or vice versa, causing a larger earthquake than if either fault broke on its own), and whether this fault or fault displays could extend beneath the plant,” a California Energy Commission research report says.
Both the USGS and PG&E geologist studied Diablo’s neighboring faults and arrived at different estimates of the highest credible magnitude earthquake that could occur on both the Hosgri Fault and the Shoreline Fault.
For the Shoreline Fault, the USGS study placed it at a maximum magnitude 6.5 and for the Hosgrie fault, a maximum magnitude 7.3. The USGS study was a collaborative study that has been peer reviewed.
Even though, according to the USGS study, the plant can withstand the highest magnitude earthquake likely to occur on the two neighboring faults, Hardebeck points at Japan’s failure to properly predict the highest magnitude earthquake that could hit the Fukushima nuclear plant, now in partial meltdown.
“Sometimes the estimates are wrong,” Hardebeck said. ‘They thought an 8.0 and they ended up getting a 9.0.”
PG&E studies of neighboring fault line were peer reviewed by geologists from five entities including Stanford University, the University of California Berkeley and the University of Southern California. Their studies placed the highest credible earthquake at a magnitude 6.5, and that is if the Shoreline Fault and the Hosgrie Fault have concurrent earthquakes.
Both PG&E officials and Hardebeck noted the differences in the type and size of faults neighboring Diablo and those off the coast of Japan.
“We do not have that type of earthquake,” Hardebeck said. “The types of faults on the Central Coast do not generate the tsunami seen in Japan. They are less disruptive.”
Several additional differences exist between the Fukushima plant and the Diablo plant. Diablo is a pressurized water reactor (PWR) and Fukushima is a boiling water reactor (BWR). PWRs have more places to cool and the steam is not radioactive, as it is at a BWR plant.
Diablo’s containment walls are 3 ½ feet deep while Fukushima are only 2 feet. Also, elevated above the Diablo plant is 5.5 million gallons of fresh water, held in two fresh water ponds that sit behind the plant at an elevation of 300 feet.
Disaster drill uncovers mistake
Every quarter, Diablo has an emergency drill to simulate several different disasters including earthquakes, terrorist attacks and forest fires. Plant employees have duties such as walking the plant to check equipment and taking radiation readings.
Once every one to two years, the plant undergoes a more fully evaluated drill by the Nuclear Regulatory Agency along with other state, local and federal agencies.
During a testing in Oct. 2009, personnel discovered a system to pump water into the reactor during an emergency had been accidentally disable for 18 months. Plant engineers had shortened the distance between a pair of valves to lessen the time it took to open them.
What they didn’t know, was two other valves where interlocked with the first pair.
While opponents of nuclear energy contend these types of incidents are frequent and unforgivable, PG&E points out that in the case of an emergency, plant operators could have opened the valves manually.
In addition to drills, the plant does radiation testing on an ongoing basis utilizing more than five different types of monitoring equipment.
For example, more than 10 environmental off-site radiation monitors located throughout San Luis Obispo County constantly monitor gamma radiation levels. Every minute, the monitors send information back to the plant.
As of Friday morning, no detectable radiation from Japan was noted on any of the monitors in San Luis Obispo County. All sensors at PG&E have been recording normal, natural background readings.
Proponents of nuclear energy note that the cost of electricity production at nuclear plants is less than half the cost of energy produced by natural gas, while opponents point at the cost of retrofitting the plant.
Dave Weisman, with the Alliance for Nuclear Responsibility, said the $4.4 billion it cost to retrofit the plant after the discovery of the Hosgri Fault fell on the backs of the rate payers.
Diablo, which along with the San Onofre nuclear plant generates more than 12 percent of California’s electricity, is requesting to renew its operating licenses that expire in 2024 and 2025.
“Now they want another 10 to 20 years,” Weisman said. “Last time it cost $4.5 billion to retrofit the plant. What will it cost now?”