The Japan Quake and the Kashiwazaki-Kariwa Nuclear Plant

By now, most of you have already heard about the earthquake that struck parts of Japan overnight, an event that killed 8 and injured 900. As the result of the quake, the Kashiwazaki-Kariwa Nuclear Plant experienced two separate incidents:

Four of the seven nuclear reactors at Tokyo Electric Power Co.'s Kashiwazaki-Kariwa nuclear power station, the world's largest nuclear power plant in terms of power output capacity, were operating or set to commence operation at the time of the earthquake and automatically shut down after sensing the strong quake.

But an electric transformer outside one of the reactors caught fire shortly after the quake. The fire was extinguished about two hours later. No radioactive leak has been detected.

It was the first fire at a nuclear plant to be caused by a quake and the Ministry of Economy, Trade and Industry is checking the cause, METI officials said.

TEPCO announced later in the day that water containing radioactive material leaked from one of three reactors that had suspended operations for regular checks and some of the water was released into the nearby Sea of Japan.

But the level of the radioactive material in the water was below the legal standard, the utility company said.

In response, NEI's Steve Kerekes passed along some notes to keep in mind as press reports continue to come out of Japan:

U.S. nuclear power plants are built with a defense-in-depth philosophy that uses multiple safety barriers and redundant, physically separated safety systems to assure that public health and safety is assured even in severe circumstances like hurricanes and earthquakes.

• The three main protective barriers are the zirconium cladding on the ceramic pellets of uranium fuel; the reactor vessel and cooling system; and the containment structure that surrounds the reactor and other major components.
• Examples of the robust design elements include: several feet of steel reinforced-concrete in the containment structures; stainless steel liners within the containment structure and within the many feet of concrete in the used fuel pools, below-grade foundations for the reactor core structure; and reinforced pipe and tank supports.

All U.S. nuclear plants are designed to withstand earthquakes of a magnitude that is equivalent to or greater than the largest known earthquake for region where it is being built. “Withstand” means that you retain the ability to safety shut down the plant without a release of radiation.

• Given the seismic history in California, for example, plants in that state are built to withstand a higher level of seismic activity than plants in many other parts of the country. They are designed with events like that which occurred in Japan in mind.
  

Initial press reports out of Japan suggest that the level of radioactivity in the water that leaked from unit 6 of the power station is very small – not only at a level that would not jeopardize public health and safety but even below reportable regulatory limits.

• We do not have details regarding the radionuclides involved in the leak, nor on the manner in which the leak occurred. We have been told by Tokyo Electric officials that the release of the water containing radioactive isotopes has been stopped.

More details are they become available. For more on the "defense in depth" philosophy that comes into play with nuclear plant safety, click here.