Imagine that a large earthquake occurred March 11, 2011, on the Hosgri or Shoreline fault off the coast of California instead of offshore from the Fukushima nuclear plant in Japan. Studies have shown that such an earthquake could shake the Diablo Canyon Nuclear Plant more than it is designed to withstand.
As a result, pipes could break and drain cooling water from the reactor vessels. Excessive shaking could also damage the systems needed to provide makeup cooling water. As a minimum, the earthquake would likely knock down electrical power transmission lines to disconnect Diablo Canyon from its normal supply of electricity. If they survived the quake, the emergency diesel generators would power emergency systems for cooling the reactor cores as they had done at Fukushima.
A tsunami wave spawned by the earthquake arrived at the Fukushima site approximately 45 minutes after the earthquake hit. Flooding submerged and disabled the backup sources of electricity at Fukushima. A large earthquake offshore of Diablo Canyon would not likely flood the site. As shown in the figure, the Diablo Canyon plant is 85 feet above sea level, compared to Fukushima being only 20 feet above sea level. The tsunami wave neared 45-feet tall when it struck Fukushima. It would take a wave nearly twice as tall to cause flooding at Diablo Canyon.
The one-two punch of an earthquake that took away the normal power supplies and a tsunami that took away the backup power supplies doomed Fukushima and triggered three reactor core meltdowns. Diablo Canyon is not vulnerable to that one-two punch, but it could easily succumb to another one-two combination.
An Earthquake-Fire Scenario
The Nuclear Regulatory Commission examined fire hazards during a briefing on July 17, 2008. An NRC senior manager informed the Chairman and Commissioners that “Approximately one-half of the core damage risk at operating reactors results from accident sequences that initiate with fire events.” In other words, the fire hazard roughly equals all other hazards combined. And that analysis assumed the NRC’s fire protection regulations were being met—the risk goes up when the fire regulations are not met.
Fire is a large risk for the same reason that flooding caused so much trouble at Fukushima. Fires and floods can disable primary safety systems and their backups. If workers are unable to recover disabled equipment or connect temporary replacements, reactor cores overheat and melt down.
The nuclear plant fire hazard is not speculative. In March 1975, a fire at the Browns Ferry Nuclear Plant in Alabama disabled all the emergency systems for cooling the Unit 1 reactor and most of those systems for Unit 2. Only heroic worker efforts prevented both cores from melting that day.
The NRC did not want another nuclear plant to experience another fire as bad as, or worse than, the one at Browns Ferry. It adopted fire protection regulations in 1980 intended to manage the fire risk to an acceptably low level. In the late 1990s, the NRC’s inspectors discovered that dozens of reactors, including the two at Diablo Canyon, did not satisfy the 1980 fire protection regulations. In 2004, the NRC adopted an alternative set of fire protection regulations. Owners had the choice of satisfying either set of regulations. On December 29, 2005, Diablo Canyon’s owner notified the NRC that it opted to someday implement the measures necessary to achieve compliance with the 2004 regulations. As of today, Diablo Canyon meets neither set of fire protection regulations.
A large earthquake on either the Hosgri or Shoreline faults could easily take away the normal power supply to Diablo Canyon. The large earthquake could also easily trigger a fire at the plant. Diablo Canyon uses large amounts of flammable fluids and gases in systems used in generating electricity. These systems are significantly less protected against large earthquakes than systems used to cool the reactor cores. The earthquake could break a pipe, causing flammable material to leak out and ignite.
That shaking could trigger a nuclear plant fire is not speculative. On September 20, 2008, the main turbine for the Unit 1 reactor at the DC Cook nuclear plant in Michigan failed. Large chunks of metal hurled from the spinning turbine blades when they broke then impacted metal housings and concrete walls and floors, causing the ground to shake. Pipes supplying hydrogen gas to the main generator for cooling broke. The escaping hydrogen gas ignited. The ground shaking also ruptured a buried pipe transporting water from an outdoor storage tank to fire sprinklers inside the plant. Thus, the event caused a fire while also impairing the plant’s ability to put out fires. The Cook Unit 1 reactor survived, but it had only received half the one-two punch. It retained the normal power supply to equipment that cooled the reactor core that day.
Had a large earthquake occurred on either the Hosgri or Shoreline faults on March 11, 2011, instead of offshore from the Fukushima nuclear plant, Diablo Canyon could easily have been toppled by a one-two punch. First, the earthquake could have disabled the normal power supplies for the plant. Second, a fire caused by the earthquake could have disabled either the backup power supplies or the emergency systems that cool the reactor cores, or both.
But instead of imagining an earthquake off the shore from Diablo Canyon, imagine that the U.S. government takes steps needed to protect Californians from this knockout blow. Congress would demand that the NRC enforce its fire protection regulations. And the NRC, with or without Congressional pressure, would enforce its safety regulations.