Tsunami Safety at SONGS

First – our thoughts are with the people of the Tonga Islands and the region following the massive eruption of an undersea volcano, spawning a series of tsunami waves that have traveled across the Pacific Rim.

The video below is from the Tonga Islands and shows the tsunami waves reaching the shore there.

Along our West Coast, tsunami advisories were issued soon after the eruption due to the currents that could be created from tsunami waves, even small ones. Advisories are issued for waves in the 0.3 to 1 meter range.

The largest tsunami to ever hit Southern California measured 3.4 meters and occurred in 1812, according to Dr. Neal Driscoll of the Scripps Institution of Oceanography. Dr. Driscoll’s 2017 research of the undersea structures offshore from SONGS found helpful conditions for preventing large tsunami from striking the area. First, there is no historical evidence of underwater landslides that would generate a large near-field tsunami. The second is the baffling effect created by the California Borderlands, the offshore sea floor topography of canyons and peaks which would muffle any far-field tsunamis. This data comes from his 2017 detailed study. The presentation he gave to the SONGS Community Engagement Panel is available here.

Sea Wall 3
View of the sea wall in front of the spent fuel storage systems at SONGS on Saturday, Jan. 15.

Further, the spent nuclear fuel at SONGS is protected by a 28-foot high sea wall. Also, the systems are designed to be inundated by 50-feet of water and still perform their safety functions.

An SCE tsunami hazard analysis found:

Submersion of the modules does not adversely affect the thermal analysis for the self-cooling dry storage cask system. The dry cask system needs no electric power for cooling since it is a totally passive system. Any blockage would be identified during post-tsunami inspections. The reinforced concrete storage modules are designed to safely withstand tornado-generated missiles traveling at high velocity, including wooden telephone poles, steel pipes, and large deformable objects (e.g., automobiles) traveling at least 185 feet per second (over 100 miles per hour). Any debris moving with the tsunami wave would have a velocity much less than the tornado missiles for which the modules have been analyzed.

In May 2020, the CEP held a meeting focused on so-called “outlier events” that included seismic and tsunami scenarios. The information developed for that meeting was extensive and included many outside experts. Access to the meeting video, presentations and document libraries is available here.