Japanese Prime Minister Yoshikhiko Noda said on Friday that the battle to stabilize the country's Fukushima nuclear plant had turned a corner, nine months after an earthquake and tsunami sent reactors into meltdowns.
"The reactors at the Fukushima Dai-ichi nuclear power plant have reached a state of cold shutdown," Noda said at a nuclear task force meeting in Tokyo. "Now that we have achieved stability in the reactors, a major concern for the nation has been resolved."
The "cold shutdown" refers to a condition where the water that cools nuclear fuel rods remains below boiling point, meaning that the fuel cannot reheat.
'Battle not over'
The Fukushima Daiichi plant, 240 km (150 miles) northeast of Tokyo, was damaged on March 11 by a huge earthquake and a tsunami, knocking out its cooling systems, triggering meltdowns and radiation leaks. It was the world's worst nuclear disaster since Chernobyl, which occurred 25 years ago.
Noda said he hoped conditions would improve quickly so that displaced people could return home.
He cautioned that it will take decades to dismantle the plant completely. "There are many issues that remain," Noda said. "Our battle is not over."
The Japanese premier said the government would "set a clear roadmap" to decommission the plant as soon as possible. Noda said the next phase would focus on the clean up operation, including decontaminating the ground around the plant.
Earlier this month, clean up crews at the plant, began offsite decontamination of public buildings, school play areas and roads around the facility. Experts say removing radioactive substances from surfaces covered with asphalt or cement is much easier than decontaminating natural soil layers.
"One possibility is using high-pressure cleaners," Wolfgang Raskob, an expert on nuclear security research at the Karlsruhe Institute for Technology told Deutsche Welle.
The important thing, he said, is to collect the waste water during the procedure because it's easier to clean radioactive water than to clean other substances with high levels of radioactive contaminants
Radioactive water easier to clean
Raskob pointed out that contaminated ground water usually doesn't pose a huge problem after nuclear accidents like the one in Fukushima because the radioactivity is usually discharged over a large area.
Rain plays a major role in flushing the radionuclides, atoms with an unstable nucleus, out of the atmosphere.
"You then very soon have a dilution of 100,000 to a million depending on how big the ground water level is," Raskob said. That, he added, usually leads to a low-level, long-lasting contamination, which is "definitely measureable but probably not really harmful to human health."
Even when radionuclides are detected in ground water, they are easy to remove. Water treatment facilities usually use a procedure called ion exchange – the same as is used to protect water kettles from calcification, Raskob said.
He said even strongly contaminated water is relatively easy to clean. Since June, engineers at Fukushima have been using a huge water decontamination facility. That became necessary after emergency cooling technology in four reactors went offline.
Workers were forced to use sea water to cool the reactors after fresh water reserves dwindled. Waste water built up and large amounts of contaminated liquid escaped into the sea, prompting concerns about the impact on the ocean.
But experts say the problem has now been largely resolved. The decontamination plant cleans an estimated 1,000 tons of water each day. The engineers now manage to remove almost all radionuclides during the process, Raskob said.
Decontaminating soil a huge challenge
The tougher challenge, he said, lies in decontaminating top soil and surrounding fields because the radionuclides are lodged deep in the earth, spelling ruin for agriculture and livestock farming.
One form of radioactive material released after the Fukushima disaster was caesium-137 which has a half-life of 30 years and poses a long-term health risk if absorbed by the soil in significant quantities.
"The caesium wanders down to the crystal structures of clay in loamy soil and remains firmly entrenched there," Raskob said. "Each year, it penetrates deeper soil layers at a speed of one to two centimeters."
Just five centimeters of contaminated soil can create huge mountains of earth that needs to be disposed of. It is still not clear where the contaminated earth can be disposed.
A dead zone for decades?
The nuclear crisis has forced more than 80,000 people to leave the area. Radiation levels in some places are still too high for them to return. Workers have erected a 20-kilometer (12 miles) exclusion zone around the plant.
Concerns have also been mounting after contamination was found in foodstuffs from the Fukushima region including rice, beef and fish.
Earlier this week, the government said it could take up to 40 years to decommission the plant fully and clean up surrounding areas.
That view is echoed by Raskob. "I don't think this highly contaminated region will be inhabitable any time soon," he said.
Author: Fabian Schmidt (sp)
Editor: Nathan Witkop