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source : japantimes.co.jp

Warning to the wise on nuclear plant risks

By MICHAEL RICHARDSON

SINGAPORE — Whether Japan's nuclear reactor and spent fuel crisis is contained or becomes worse, it has raised concerns about the risks of generating electricity from atomic power, especially in places that are prone to earthquakes and tsunami.


If Japan, a leader in science and technology, has trouble coping with such risks, should rapidly growing Asian states that need reliable electricity supplies review their nuclear expansion plans?

More than 155 power reactors are planned and over 320 others proposed. Most of the planned reactors are in Northeast, Southeast and South Asia. Sixty are under construction worldwide. If all the others were to go ahead, they could more than double nuclear generating capacity by 2030.

Of the 440 nuclear power reactors already operating in 31 economies and generating about 15 percent of the world's electricity, one-fifth are in areas of significant seismic activity, according to the World Nuclear Association.

Analysis based on a seismic hazard study carried out by the U.S. Geological Survey and the Swiss Seismological Service shows that nearly 50 of the world's operating reactors are in areas known to have at least moderate earthquake activity, including the stricken Fukushima No. 1 nuclear plant at the center of Japan's worst nuclear accident.

Fourteen of the reactors, mainly in Japan and Taiwan, are in areas of high activity. Of the 14, 10 are located on coastlines, putting them at risk of both quakes and the tsunami they trigger.

Many nuclear power reactors are built along coastlines so that they can draw as much cooling water from the sea as they need. To run in the most cost-efficient way, these plants often contain multiple reactors.

The Fukushima plant on Japan's northeast coast, not far from the epicenter of the violent March 11 earthquake, that sent powerful pressure waves crashing onto the shoreline, has six reactors that can generate almost 4,700 megawatts of power.

Japanese and most other nuclear plants are designed to withstand earthquakes and, in the event of a major earth movement, to shut down safely. Because of the frequency and magnitude of earthquakes in Japan, special attention is paid to the siting, design and construction of nuclear reactors.

However, the 9.0-magnitude quake was one of the strongest ever recorded. Three of the Fukushima reactors were running and shut down automatically. The other three units were inactive.

But even offline reactors have nuclear fuel, in reactors and in adjacent storage ponds after they have been used. The fuel, in zirconium-clad rods containing uranium and in some cases plutonium, must be kept cool to prevent possible overheating and the release of toxic radioactivity into the atmosphere.

At the Fukushima plant, each reactor is surrounded by a primary containment vessel made of thick and specially strengthened steel. It provides the most critical line of defense against a radiation leak. The reactors are housed in a bigger containment building made of steel and concrete to form a final line of defense.

However, the spent fuel pools are outside the containment structure designed to trap radiation leaks. They are also high above the ground near the top of the reactor vessel. In an earthquake, the intense shaking is magnified at this height and the "sloshing" effect can spill much of cooling water and cause other damage.

Tokyo Electric Power Co., the utility operating the Fukushima plant since it was built in the 1970s, has said that more than 11,000 spent fuel rod assemblies are stored on site. This is about four times as much radioactive material as in the reactor cores combined.

While Fukushima's reactor vessels apparently withstood the stress of the quake, the electricity grid providing them with power did not and failed. Worse still, most backup emergency diesel generators failed, evidently due to damage from the 7-meter tsunami surge that struck the plant.

The lack of water for cooling set off a chain reaction of overheating and explosions that have jeopardized the safety of some of the reactors and their spent fuel storage ponds.

Intense efforts have been made to reconnect the power. If reliable electricity supply to the plant can be restored, it may be possible to bring the situation back under control without a serious radiation leak, providing pumps and other critical machinery have not been damaged beyond repair.

Either way, Asian states like China, South Korea and India that are expanding nuclear power, as well as those in Southeast Asia that are planning or considering whether to become nuclear power producers, should review their programs in light of what has happened in Japan to ensure that they use the safest possible reactor designs and spent fuel-storage systems.

Some of these countries, including Indonesia and the Philippines, lie on a geologically unstable fault line around the Pacific basin that also runs through Japan and Taiwan. This so-called Ring of Fire is an area prone to volcanoes, earthquakes and tsunami.

It is clearly bad policy anywhere to store used fuel close to reactors high aboveground and without a solid containment shield to prevent radioactive releases in the event of earthquakes or accidents.

Is it also unacceptably risky policy to site a nuclear power plant anywhere other than in a geologically stable zone?

The International Atomic Energy Agency, the United Nations body responsible for advising countries on nuclear safety standards, should publish a seismic risk assessment for each country that generates electricity from nuclear power or plans to do so. National governments would then have an objective gauge against which to measure the risk of earthquakes and tsunami to the safe operation of their nuclear plants.



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