Must read report from California Coastal Commission re: earthquakes and nuke plants.

[Cleita]

http://a4nr.org/wp-content/uploads/2011/04/032411-CCC-Tohoku-+-CA-report.pdf

Notable in the report are:

<snip>

Implications for California Nuclear Power Plants and Spent Fuel Storage
Facilities

There are two operating nuclear power plants in the California coastal zone and one nuclear plant
undergoing decommissioning. The Diablo Canyon Power Plant (DCPP) in San Luis Obispo
County and the San Onofre Nuclear Generating Station (SONGS) in northern San Diego County
are operating power plants that hold current licenses from the Nuclear Regulatory Commission
(NRC). The nuclear unit of the Humboldt Bay Power Plant (HBPP) near Eureka is being
decommissioned, although highly radioactive spent fuel and other materials remain on site. A
magnitude 9 earthquake near DCPP or SONGS is extremely unlikely. However, the Humboldt
Bay plant is in close proximity to the Cascadia Subduction Zone and could be subject to a
magnitude 9 earthquake.

All three facilities, including their spent fuel storage facilities, have been subject to numerous
seismic investigations. During the permitting process for the Independent Spent Fuel Storage
Installation (ISFSI) at each facility, Southern California Edison (SCE) and Pacific Gas and
Electric (PG&E) undertook new geologic investigations; particularly extensive for Diablo
Canyon and Humboldt Bay. These studies, along with studies undertaken for the original
licensing of these plants, ongoing USGS and academic studies, and experience gained from
geologically similar regions, were reviewed by the U.S. Nuclear Regulatory Commission (NRC),
which ultimately released Final Safety Analysis Reports (FSARs) recommending approval of
each facility.

During Coastal Commission review and permitting of each ISFSI, Commission staff reviewed all
of this material, conducted independent research of published literature, interviewed
knowledgeable parties, and conducted site visits at and around each facility, prior to
recommending that the Commission approve each facility. The Commission’s adopted findings
for each approval can be found at:

DCPP: http://www.coastal.ca.gov/energy/W5a-1-2005.pdf
SONGS: http://www.coastal.ca.gov/energy/e-00-14rf.pdf
HBPP: http://www.coastal.ca.gov/energy/Th6a-9-2005.pdf

The expected earthquake and tsunami risk at each facility is described briefly below.

Diablo Canyon Nuclear Power Plant

Earthquake Concerns: Although a magnitude 9 earthquake is extremely unlikely near the DCPP,
a magnitude 7.2 earthquake on the Hosgri Fault, lying only 3 miles offshore, is currently
considered possible.

The Hosgri Fault was discovered during the construction of the plant. In 1975 the NRC, in
conjunction with the USGS, concluded that that the Hosgri Fault is capable of a magnitude 7.5
earthquake, and that ground shaking at DCPP could be as high as 0.75 g. PG&E retrofitted the
plant in 1978 to withstand that level of ground shaking. In 1978 the NRC required the
implementation of a Long Term Seismic Program, through which the seismic safety at the plant
would be continuously reevaluated. In 1991, NRC approved a report from PG&E that, using
improved earthquake models, showed that the maximum credible earthquake on the Hosgri fault
was of magnitude 7.2, but that ground shaking at DCPP would be as high as 0.83 g. PG&E
demonstrated to the satisfactions of the NRC that the plant had been retrofitted in 1978 with
adequate safety margins to withstand that level of ground shaking.

The most recent study submitted to the NRC by PG&E examined ground shaking that would
result from an earthquake on the newly discovered “Shoreline Fault” located less than 0.5 miles
from the reactor building. Preliminary results of those studies indicate that the potential ground
shaking from this fault will be less that those used in the initial plant design. The report of these
studies, available at http://diablocanyonpge.com/home/resources/shoreline-fault-zone-report-
with-plates.html is currently under review by the NRC, as well as by state geologists from a
number of agencies, including the Coastal Commission.

As discussed below, AB 1632 required that the State prepare a report making recommendations
to facilitate assessing, among other things, the seismic safety of DCPP and SONGS. One of the
recommendations in that report is for further detailed investigation not only of the Shoreline
Fault, but of the total seismic environment of the plant. These studies are currently underway.
The proposed high-energy studies meant to identify seismic characteristics deep below the plant
and surrounding area will be subject to CEQA review and will require review and permitting by
the Coastal Commission.

Tsunami Concerns: DCPP is located at an elevation of 85 feet above mean sea level (MSL), atop
a high coastal bluff. It is effectively above the range of any conceivable earthquake-induced
tsunami, and is mapped as lying outside of the tsunami inundation zone on the Tsunami
Inundation Maps recently released by the California Emergency Management Agency,
California Geological Survey, and the University of Southern California.

San Onofre Nuclear Generating Station

Unit 1 of the San Onofre Nuclear Generating Station was commissioned in 1968, and was
designed to resist ground shaking of 0.67g corresponding to a magnitude 7.0 earthquake on the
nearby Newport-Inglewood-Rose Canyon Fault system. Units 2 and 3 were commissioned in
1983 and 1984 to the same design standard. Unit 1 was decommissioned in 1992, but radioactive
portions of the reactor still remain at the plant.

Earthquake Concerns: Although a magnitude 9 earthquake is extremely unlikely near SONGS, a
few studies indicate that an earthquake larger than the design-basis earthquake may be possible
near the reactor site. The Commission considered these studies in its findings for the ISFSI
approval in June 2001 and concluded that:

…there appears to be credible evidence that, in addition to the strike-slip faulting recognized at
the time of the SONGS licensing review, thrust faults exist in the area offshore of the SONGS site
which might interact with the Newport-Inglewood-Rose Canyon fault system in a complex way
during an earthquake. If these faults are active or potentially active, the increase in potential fault
rupture area has, at a minimum, the potential to increase the magnitude of an earthquake on the
integrated fault system. Geologists’ understanding of this area is rapidly evolving, and there are
few constraints on the parameters needed to assess the increase in earthquake risk (such as slip
rate on each of the potentially active faults, segmentation of the faults, and potential for cascading
failure between fault segments). One of the few published estimates is that of Shaw and his
students (Rivero et al., 2000), who hypothesize that the combined system may be capable of an
earthquake ranging from MW 7.1 to 7.6, depending on which sets of faults are involved in the
earthquake…

Shaw’s tectonic model for the area is, however, quite controversial (Jones, USGS, pers. comm.,
2001). Commission staff consulted with seismologists and geologists at the U.S. Geological
Survey, California Division of Mines and Geology, California Seismic Safety Commission, within
academia, and at private consulting firms. Although there was near unanimous recognition that
there is an increased earthquake risk given our emerging understanding of the complexities of the
region relative to a simple strike-slip model used in the SONGS seismic hazard assessments, no
one could assess the potential ground shaking that might be expected at the SONGS site.

The Commission thus finds that there is credible reason to believe that the design basis
earthquake approved by the NRC at the time of the licensing of SONGS 2 and 3—a magnitude
7.0 earthquake on the Newport-Inglewood-Rose Canyon fault system 8 km from the site, resulting
in ground shaking with a high frequency component peaking at 0.67 g—may underestimate the
seismic risk at the site. This does not mean that the facility is unsafe—although the design basis
earthquake may have been undersized, the plant was engineered with very large margins of
safety, and would very likely be able to attain a safe shutdown even given the larger ground
accelerations that might occur during a much larger earthquake.

Tsunami Concerns: Tsunami run up and inundation were considered by the SCE and NRC for
permitting of the SONGS facility. However, more recent examinations indicate that a larger
earthquake or a large submarine landslide could generate a tsunami larger than that considered
by SCE or the NRC. The potential tsunami risk was included in the Commission’s findings for
the ISFSI permit which concluded:

These studies suggest that large local-source tsunamis could be generated by mechanisms other
than those considered during licensing for SONGS 2 and 3, the basis for the 1995However, there have been no local runup studies based on this mechanism that a that are widely agreed upon, and certainly none for the SONGS site itself. As Dr. Legg indicates, tsunami runup maps are currently being prepared for San Diego County by individuals at the University of Southern California in conjunction with the Office of Emergency Services, but they are not currently available.

Commission staff accordingly concludes that although the proposed project may be threatened by
tsunami, the major effect from an earthquake-generated tsunami would be site inundation.
Possible inundation has been factored into the project design, and it would not adversely
ffect the stability of the site. There is also a potential for a submarine landslide to generate a
tsunami that could threaten this site; however, current mapping and modeling do not provide any
information of how the site would be ffected by such an event.

The maps mentioned have since been produced, and they do, in fact, place the SONGS facility in
the tsunami inundation zone:

The SONGS site was excavated into the coastal bluff and the nuclear reactors are located at an
elevation of less than 20 feet MSL. The tsunami inundation line calculated for this area is at an
elevation of approximately 20 feet MSL, and the plant is protected by a 30-foot seawall. Thus, it
appears to be protected from the modeled set of tsunamis underlying the state map. How the
inundation line on the state map might change if it included the magnitude 7.6 thrust earthquake
postulated by Shaw and others is not, however, known. Further study of the tsunami risk at the
SONGS facility appears warranted.

The report is 12+ pages long and well worth the read. It describes the possibility of very large earthquakes and tsunamis in the Cascadia zones of California, Oregon and Washington. Even though the report says that the El Diablo earthquake zones including the San Andreas fault could not produce larger than a magnitude 9 earthquake, that plant is only built to withstand a 7.5 earthquake.

[bananas]

1. The 2007 quake that took out the Japanese KK plant was also considered impossible

Turns out that quake could've been much larger, and the KK plant is right on a major faultline.