from Sunday Herald, 12 October 2014, from Fukushima
More than three and a half years after four nuclear reactors at Fukushima Daiichi on the east coast of Japan were devastated by an earthquake and tsunami, they still leak. Radioactivity is spewing into the air, leaching into the soil and seeping into the sea.
The huge scale of the containment problems faced by the plants’ operator, TEPCO, are difficult to comprehend. Highly radioactive uranium fuel in three of the reactors melted down and wrecked the water-cooling systems essential for preventing overheating.
So in order to prevent renewed chain reactions triggering another disaster, TEPCO has to pour hundreds of tonnes of water over the fuel every day. The trouble is that this becomes very radioactive, and leaks out of the bottom and mixes with groundwater heading for the Pacific.
The water is collected, filtered to remove the worst of the contamination, and then stored in over 1,000 huge tanks and ponds on the site. To date, more that half a million tonnes of radioactive water have accumulated.
But not surprisingly, given the scale of the operations, there have been leaks. A series of accidental discharges were reported in March and April 2013, the largest being 120 tonnes.
In June 2013, it was revealed that groundwater next to one of the reactors was contaminated. In August, 300 tonnes of radioactive water leaked from a tank and polluted soil.
There was another mishap in February this year, when 102 tonnes of contaminated water leaked from another tank. One solution to help combat the problem dreamt up by engineers stretches the limits of technology.
They are trying to create a 1,500-metre “ice wall” around the reactors in an attempt to reduce groundwater contamination. They are sinking a series of pipes 30-40 metres into the ground, and pumping liquid nitrogen through them to freeze groundwater into a contamination barrier.
Experts point out, however, that this may not work and, if it does, it will require large amounts of power over a long period to keep the water frozen. “I don’t know whether the technology is ready,” says Yukiteru Naka, who’s been a nuclear engineer at Fukushima for 40 years.
The techniques are “very sensitive and very difficult” and there are “many concerns” about how to monitor the effectiveness of such a large ice wall, he warns.
At the fourth reactor, the fear has been that some of the 1,500 hot and highly radioactive fuel rods stored there would lose their cooling water. If they were exposed to the air, they could start disgorging large clouds of dangerous radioactivity over Japan.
According to Naka, work to remove the fuel rods is now “almost finished”. The Fukushima Daiichi reactors are also continually discharging radioactivity into the air, though at much lower levels than during the accident.
Naka estimates it will be at least another 30 years before all the reactors are rendered safe. One problem is an increasingly acute shortage of skilled clean-up workers, he says, because they keep having to be replaced so they don’t exceed radiation safety limits.
The nightmare scenario is another earthquake, Naka suggests. The water tanks and other facilities installed since the accident in March 2011 lack foundations and supports, he points out.
“They are unstable if there’s another earthquake,” he says. “Piping and tanks systems are usually built to high regulations, but for these no attention was paid to the law. It’s only a temporary system.”
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