In the early years, the Mothers for Peace was successful in forcing the NRC and PG&E to acknowledge the problems of an error-ridden plant sited near a major active earthquake fault. The NRC, in fact, has admitted that the siting of a nuclear power plant at Diablo Canyon is in violation of current NRC regulations. Many questions remain unresolved regarding earthquake, plant operation, and waste-storage hazards.
Some highly qualified geologists have questioned the nature of the Hosgri Fault which lies only a few miles from the plant. Risk assessments and emergency plans had assumed the Hosgri to be a “strike/slip” fault, meaning that land masses grind past each other horizontally. However, there is now significant evidence that the fault might be a “thrust” fault, in which one section of earth is being forced upward over another. Thus, there are grounds for concluding that the Diablo Canyon Nuclear Power Plant was not designed or reinforced to withstand the even greater destructive ground motions caused by this type of fault. Recent earthquake activity offers a vivid reminder of one of the many significant risks of nuclear power.
The Northridge Earthquake of January 1994 was the result of a “thrust” fault. The December 2003 earthquake in San Luis Obispo County came from a portion of the San Simeon/Hosgri fault system previously thought to be “inactive.”
In November of 2008, a second, previously unmapped fault was discovered offshore from Diablo Canyon. It is thought to be smaller than the Hosgri fault but is closer to shore and could interesect with the Hosgri. This fault raises new questions regarding the seismic risks associated with the continued operation of the nuclear plant and storage of high-level radioactive waste.