2003 Recent Seismic History

There are multiple issues that must be studied before decisions can be made regarding the proposed dry cask system of storing high level radioactive waste.

Jane Swanson, spokesperson for the SLO MFP asserts that "It is premature to make any decisions regarding the future of the Diablo Canyon nuclear plant. The recent earthquake has not yet been thoroughly studied and assessed by the United States Geological Survey or other impartial, scientific authorities."

Issues that need to be thoroughly studied before decisions can be made on PG&E's proposed dry cask system of storing additional radioactive wastes include the following:

* In 1984 and 1986, the NRC granted licenses to operate the two nuclear units at Diablo Canyon, based on the assumption that a quake generated on the Hosgri earthquake fault two and a half miles away would be the result of a strike/slip fault, one that moves horizontally. The Dec. 22 earthquake was on a fault apparently connected to both the Hosgri and San Simeon faults. Observations indicate that it may have been generated by a thrust fault, and not a strike/slip fault. A thrust fault moves one portion of earth under another, and causes much more ground acceleration and structural damage than a strike/slip fault. No plans for additional waste storage at Diablo or for any extension of the operating license should be considered until all new seismic information has been thoroughly studied.

* The Dec. 22 earthquake came from a portion of the San Simeon/Hosgri fault system previously thought to be "inactive". Since the 1980's when Diablo was licensed, much new information about thrust faults has been learned from the Northridge, Coalinga, and recent oceanic earthquakes. This information has not yet been thoroughly analyzed for its relevance to the structural design and seismic bracing of the Diablo Canyon plant. To ignore this new information could be extremely costly to our county.

* After it was discovered that the Diablo Canyon Unit 2 had been built in reverse, due to a mirror-image misreading of the blueprints, PG&E spent billions of dollars to re-do the seismic bracing of that unit. But the bracing installed was designed to protect the plant from the effects of horizontal movement, not the vertical movement recently observed from the related fault 50 miles away. No decisions should be made until thorough studies have been completed to show what the connection between the December 22 earthquake might be, and whether there is the potential for a thrust fault to be generated by the Hosgri fault.

* The energy release from the recent earthquake was directional rather than concentric, and the direction was to the south/east. This may have implications for future earthquakes on the Hosgri fault, since Diablo lies east of the fault line. We need to give geologists a chance to assess this probability before even considering adding to the hazards of the nuclear plant.

* Within 10 minutes of the recent earthquake, PG&E reported that there was no damage to the plant. Perhaps there was no visible damage, but pipes and welds need to be X-rayed to be sure that there is not weakening that could lead to serious trouble next time a given pipe or weld is subjected to stress.

* MFP has long argued that the Diablo Canyon plant should have cement or other protective containment structures over its pools of nuclear waste storage, and also over dry casks should they be allowed. In the event of an earthquake causing a loss of borated water in the existing spent fuel pools, or in case of accidental or terrorist-caused damage to the proposed dry cask storage, a containment structure would at least buy time, hopefully time to allow those living closest to the plant to evacuate.