Fukushima triggers new look at mega-quake threat

A man clears rubble from his destroyed shop in the city of Ofunato
A man clears rubble from his destroyed shop in the city of Ofunato. The disaster that has befallen Fukushima is prompting some experts to cast a worried eye at the risk of massive earthquakes to nuclear plants in seismic zones.

The disaster that has befallen Fukushima is prompting some experts to cast a worried eye at the risk of massive earthquakes to nuclear plants in seismic zones.

Twenty percent of the 440 commercial reactors in operation around the globe are located in areas "of significant ," according to the World Nuclear Association (WNA), an industry group.

Some of the 62 additional reactors under construction are also in quake-prone zones, along with many of the nearly 500 units on order or proposed, especially in fast-developing countries.

Many plants -- including the four Fukushima reactors crippled by the March 11 tsunami -- are located on or near coastal areas in the "Ring of Fire", a 40,000-kilometre (25,000-mile) arc of tectonic faults circling the Pacific.

The nuclear industry stresses that location in a is not by itself a problem.

Engineering norms meet scientific estimates, it says.

Reactors are generally designed to withstand "the largest earthquake which can reasonably be expected to occur at the site of a ," according to the WNA.

But some seismologists are questioning these calculations, given often-sketchy data about when truly exceptional quakes -- such as the 9.0-magnitude monster of last Friday -- can strike.

Such events sometimes occur only once in hundreds of years, or more, but the historical record may be poor.

"We clearly need to have a reassessment of the probability for these kinds of quakes to occur, particularly in seismically hazardous areas like Japan," said Bob Holdsworth, a professor of structural geology at the University of Durham, England.

"The Japanese underestimated the size of earthquakes that could strike this region," said Ross Stein, a at the US Geological Survey (USGS) who specialises in faults in and near Japan.

"We probably should re-evaluate our estimates of the maximum sizes of earthquakes that could strike all fault areas," Stein said by phone.

What happened in Japan "is clearly an indication that we haven't properly thought about events that are well outside our historical experience but nonetheless possible. For me, that is the broad implication for all of us in this field about the weaknesses of our thinking."

Virtually all Japan's reactors are at high, or very high, risk of hazard from severe ground shaking over the next half-century, according to the Global Seismic Hazard Map, compiled by the UN and half-a-dozen national scientific bodies, including the USGS.

Based on geological and historical records, the hi-tech tool shows the peak ground acceleration (PGA) that a site can expect during the next 50 years with 10 percent probability.

PGA is the standard index of earthquake acceleration at ground level. Unlike the Richter and moment magnitude scales, it is not a measure of the total energy of a quake, but rather how hard the earth shakes in a given area.

About half of China's dozen active reactors are in zones of "moderate" risk. South Korea's reactors, which provide more than 30 percent of the country's electricity, are shown at low risk on the Hazard Map.

Taiwan's half-dozen reactors are in a "high" hazard zone, along with four reactors in California, and one in Washington state.

Outside the Ring of Fire, the most quake-prone region with active nuclear installations is in south and central Asia.

Installations in Pakistan and one in northern India are at moderate-to-high risk on the scale, along with two reactors -- one under construction, the other planned -- in Iran.

In Europe, the seismic threat to nuclear installations is thought to be far lower, with the possible exception of several small, experimental reactors in southeastern France which are near a known fault.

France, which derives more than three-quarters of its power from nuclear, has stoutly defended this energy source and its reactor designs.

"All French nuclear plants have been designed with seismic risk and flooding risk factored in," Industry Minister Eric Besson said on Saturday.

"We don't wait for an accident to happen in Japan to raise the question over here, but this doesn't mean that we can't re-evaluate the situation."


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Mar 15, 2011
What happened in Japan was not the case of "not planning for earthquakes," it was more a situation where the operators of the reactors were not the engineers who drew the fault trees and designed the reactors for any conceivable sequence of disasters.

Think about what happened. A large earthquake apparently caused no damage to the reactors, turbines, or cooling systems. But automatic trips shut the reactors down "to be safe." The backup diesel generators on-site started up to insure a continuing supply of electricity for the pumps in case the rest of the electrical grid went down. Then the tsunami hit. The reactor buildings could have withstood a bigger tsunami--but the diesel generators were not designed to be submarines. And of course, the tsunami took down all the high-tension wires that connected to the electrical grid. One last disaster, the tsunami dumped tons of mud and debris into the heat exchangers that transferred heat from the (pure) cooling water to sea water.

Mar 15, 2011
Can't help but feel sympathy for the Japanese, between the record-breaking earthquake, tsunami, nuclear meltdowns and to top it all off the closing of their factories, I really hope the situation improves for them.

Mar 15, 2011
There were three points at which disaster might have been averted. Well, one big point before the earthquake with plenty of time for planning. The first was to catch the automatic earthquake trip in progress on one or more of the reactors, realizing that dealing with the tsunami would require a reliable source of on-site power--and the diesel generators were not going to be it. If you SCRAM most power reactors there is no way you can restore them to operation within eight hours or so. "Delayed" neutrons and short half-life reactor poisons (that drink up neutrons) are balanced during full power operation. But SCRAM the reactor (rapidly drive the core below criticality), and you are left with a core full of poisons.

During a normal shutdown, you can "catch" the reaction at a lower level. The reactor will then produce power, but not full power, which would have been nice. However, I doubt any operator had the guts to try that after Chernobyl.

Mar 15, 2011
The other way to have averted the worst of the disaster would have been to shut down at least one of the diesel powered generators until after the tsunami. Some clean up and jackleg wiring might be needed after the tsunami, but a diesel engine that drinks seawater is a pile of scrap iron.

The final opportunity to avoid disaster would have had to happen at all of the operating reactors. SCRAM them, which in the case of boiling water reactors sprays water containing boron over the core. Now you are taking the reactor out of service for say a month, to get enough boron back out of the reactor core, reset the emergency systems, etc.

How long did the operators have to choose that option? I don't know. Depends crucially on how much information they had, and the timing of events. Before the tsunami hit? Sure, if you know it is coming. Also as the reactor starts to cool down--thermal not nuclear--there should still be enough steam pressure to power the emergency injection system.

Mar 15, 2011
@eachus
Please continue. I'm interested to hear more from you. Have you worked in the Nuclear industry?

Mar 15, 2011
This disaster was so extreme that it obviously pushed the nuclear plant beyond the stresses it was designed to handle. We can all see the need for plants to have better cooling systems / trips / backups etc in case of a disaster like this and undoubtedly this will be factored in to future designs.

I'm not a green activist or anything, but I can't help but point out the simlpe logic here - this nuclear emergency would not have happened if there was no nuclear plant in the first place. This should be a wake up call for more investment in energy generating technology (as clean as existing hydro/wind but as powerful as nuclear).

Mar 16, 2011
Well, they've been touting that modern nuclear reactors are safe... honestly, if it takes disasters on an apocolyptic scale like this... earthquakes, tsunamis, and volcanoes, then I'd say they're pretty safe... The only thing I might've added as another safety system would be some kind of cryogenic cooling system for emergencies. Then again, I'm not a nuclear physicist, and don't know if rapid cooling to sub-zero temperatures can have a detrimental affect on a nuclear reactor's stability...

Mar 16, 2011
Incidentally... Apple announced today that they're delaying the ipad2 release in Japan...
http://www.physor...pan.html

My only comment is... at the bottom of that article.

Mar 16, 2011
Well, they've been touting that modern nuclear reactors are safe... honestly, if it takes disasters on an apocolyptic scale like this... earthquakes, tsunamis, and volcanoes, then I'd say they're pretty safe... The only thing I might've added as another safety system would be some kind of cryogenic cooling system for emergencies. Then again, I'm not a nuclear physicist, and don't know if rapid cooling to sub-zero temperatures can have a detrimental affect on a nuclear reactor's stability...

As I understand it, the reactors experiencing the problems are not modern.

As to cryogenic cooling, I am not a nuclear scientist myself, however, as I see it, what is needed is a way to prevent neutron flow. That stops the reaction. I highly doubt that cryogenic cooling on its own would stop the nuclear reaction.

Mar 17, 2011
Or you could simply build a concrete structure to divert a giant wave away from your generators/sensitive areas if your reactor is near a hazardous coast.

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