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Tuesday, April 12, 2011

Experts urge external cooling system


Staff writer

The Fukushima No. 1 nuclear crisis has been raging for a month, shattering Japan's reputation as a safe, advanced nation and attractive tourist destination.

The situation is so bad that experts and government officials aren't even sure how many months it will take to bring the plant under control.

Tokyo Electric Power Co. urgently needs to repair the plant's damaged cooling systems or even construct a whole new external plant to lower the temperature of the reactors to less than 100 degrees to stabilize the blazing fuel rods inside.

It must also keep the spent-fuel pools above them cool.

But highly radioactive water believed to be leaking from somewhere deep inside the troubled reactors has flooded the basements of their turbine buildings, hindering any attempts to repair the damage.

Experts agree that plugging the leaks and removing the toxic water are currently the top priorities as they embark on the long and unpredictable path to ending the crisis.

"The leakage (from the reactors) has to be stopped. Leaking means the water inside the reactors is decreasing. So the water has to be replenished, and then it leaks again. This cycle has to be stopped," said Hisashi Ninokata, professor of nuclear reactor engineering at the Tokyo Institute of Technology.

The water that came into contact with the fuel rods has been leaking into the turbine buildings. The basement floor of reactor No. 2's turbine building is especially contaminated.

About 60,000 tons of contaminated water is estimated to have flooded the turbine buildings of reactors 1, 2, 3 and 4, as well as some trenches beneath them. Tepco has been attempting to pump the water out and transfer it to other tanks and containment facilities, but progress has been slow and safe places to put it are hard to find.

Workers are desperately trying to remove the water because it is blocking repairs to the residual heat removal system — the permanent cooling system knocked out by the March 11 tsunami.

Some experts, including Ninokata, have started floating the idea of temporarily building a brand new external cooling system for the reactors, given the daunting task of removing the deadly water in the building housing the RHRS.

"It will probably take half a year or a year to restart the RHRS, so the external cooling system needs to be used during that period of time," he said, adding that the work to set one up could be finished in a few weeks once the decision is made.

But Ninokata also proposed another step. Since there is a chance the existing RHRS was severely damaged by the tsunami, it might even be better, in addition to an external cooling system, to set up a brand new RHRS right outside the turbine building. This could be completed in a couple of months, he said.

Akio Koyama, professor at Kyoto University's Research Reactor Institute and an expert on managing radioactive waste, said Japan has no experience removing or processing such a large amount of extremely contaminated water, so the work will be challenging.

Once the toxic water has all been pumped out, it might be transported to other plants around the country for processing. But existing facilities are not designed for such high-level radioactive water and are probably unable to handle it, Koyama said. A new facility will be needed to decontaminate and safely dispose of it, he said.

The scope of the disaster has grabbed the world's attention.

Countries sensitive to radiation have banned sales of Japanese products, particularly seafood and vegetables, over health fears. South Korea and Russia blamed Japan for dumping thousands of tons of radioactive water directly into the sea without advance consultation. And Japan has been late disclosing rising levels of cesium in the ocean.

Ninokata said it is true the Fukushima accident has proven that the industry's tsunami safeguards failed. But he also said it would not be a repeat of Chernobyl.

The chances of a hydrogen explosion are low because Tepco has taken measures, including injecting nitrogen into the reactors to purge them of hydrogen, to avoid further explosions of the type that blew the roofs of some of the reactor buildings sky high.

But even if another explosion occurs, the containment vessel will not explode, although it might be damaged, he said.

What's more, unlike Chernobyl, where the graphite moderators burned and released massive amounts of radioactive material into the air, there are no flammable materials inside the Fukushima reactors.



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The Japan Times

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