Thursday, March 17, 2011

Will We Turn Japanese?

I really don't think so.  But that doesn't mean we shouldn't consider the possibility.  The massive earthquake and terrible, devastating tsunami that struck Japan last week are unlikely to hit the US, except in the Pacific Northwest and Alaska.  Those are the only places close to the US where there are subduction zones, which are a type of tectonic plate boundary that is responsible for the largest earthquakes, and most tsunamis.  Coastlines are also vulnerable to tsunamis caused by underwater landslides, which may or may not be initiated by earthquakes.   In the immediate region of a small slide, tsunamis can still be large.  Very large slides can cause tsunamis that affect entire ocean basins.  The frequency of landslide-induced tsunamis is unknown at this point, but the risk on the entire west coast is much higher than elsewhere, again because there are active plate boundries nearby. 

Here are the nuclear power plants in the US close to a shoreline:
  • On the West Coast, there are two nuclear plants with four reactors adjacent to the ocean: Diablo Canyon Units 1 and 2, and San Onofre Units 2 and 3.  Two additional reactors have been shut down and decommissioned: Humboldt Bay Unit 1, and San Onofre Unit 1.
  • On the Gulf of Mexico, there is one plant with one reactor situated on the coast: Crystal River Unit 3.
  • One Gulf region plant with one reactor is located in a low-lying inland region that may be affected by storm surges: Waterford Unit 3.
  • On the East Coast, only one plant with two reactors is situated directly on the Atlantic Ocean: Saint Lucie Units 1 and 2.
  • Six East Coast plants with nine reactors are located behind barrier islands: Seabrook Unit 1, Pilgrim Unit 1, Millstone Units 2 and 3, Oyster Creek Unit 1, Brunswick Units 1 and 2, and Turkey Point Units 3 and 4.  The islands and shallow lagoons behind them may or may not be large enough to stop a tsunami from flooding the facilities.  Millstone Unit 1 has been decommissioned.  Shoreham Unit 1 never operated at commercial levels, and has been dismantled.
  • Five more East Coast plants with nine reactors are located on tidal rivers at varying distances from the ocean: Hope Creek Unit 1, Salem Units 1 and 2, Indian Point Units 2 and 3, Calvert Cliffs Units 1 and 2, and Surry Units 1 and 2.  The locations may or may not be far enough upstream to be protected from tsunami-induced flooding.  Two additional reactors have been shut down: Maine Yankee Unit 1, which has been decommissioned, and Indian Point Unit 1, which is still standing.
The only way to determine if these plants are actually at risk is to model a flood event and quantify the sea level rise.  Simply looking at the height or distance from the shoreline isn't enough.  The specifics of the coastline and bathymetry at each location can have significant effects on the run-up.  After that task is done, the containment structure and safety systems can be analyzed to see if they would remain intact and operating.  While this has certainly been done already for each plant, the question is whether it has been done with the right assumptions.  For instance, the plants on the northeast coast of Japan assumed the subduction zone offshore would not produce anything greater than a 8.0 earthquake.  That turns out to have been wrong, and the resulting tsunami was underestimated as a consequence.

Equally important as redoing analyses is actually verifying the safety systems work.  TEPCO, the owner/operator of Fukushima Daiichi, has been accused of not verifying the functionality of some of the safety systems.  Whether that is true will be worked out over the next few months.  But there should be another round of testing of each plant in the US regardless of the outcome.

No comments: