31 Août 2016
August 30, 2016
By MARTIN FACKLERAUG. 29, 2016
FUKUSHIMA DAIICHI NUCLEAR POWER STATION — The part above ground doesn’t look like much, a few silver pipes running in a straight line, dwarfed by the far more massive, scarred reactor buildings nearby.
More impressive is what is taking shape unseen beneath: an underground wall of frozen dirt 100 feet deep and nearly a mile in length, intended to solve a runaway water crisis threatening the devastated Fukushima Daiichi Nuclear Power Station in Japan.
Officially named the Land-Side Impermeable Wall, but better known simply as the ice wall, the project sounds like a fanciful idea from science fiction or a James Bond film. But it is about to become a reality in an ambitious, and controversial, bid to halt an unrelenting flood of groundwater into the damaged reactor buildings since the disaster five years ago when an earthquake and a tsunami caused a triple meltdown.
Built by the central government at a cost of 35 billion yen, or some $320 million, the ice wall is intended to seal off the reactor buildings within a vast, rectangular-shaped barrier of man-made permafrost. If it becomes successfully operational as soon as this autumn, the frozen soil will act as a dam to block new groundwater from entering the buildings. It will also help stop leaks of radioactive water into the nearby Pacific Ocean, which have decreased significantly since the calamity but may be continuing.
However, the ice wall has also been widely criticized as an expensive and overly complex solution that may not even work. Such concerns re-emerged this month after the plant’s operator announced that a section that was switched on more than four months ago had yet to fully freeze. Some also warn that the wall, which is electrically powered, may prove as vulnerable to natural disasters as the plant itself, which lost the ability to cool its reactors after the 45-foot tsunami caused a blackout there.
The reactor buildings are vulnerable to an influx of groundwater because of how the operator, Tokyo Electric Power Co., or Tepco, built the plant in the 1960s, by cutting away a hillside to place it closer to the sea, so the plant could pump in water more easily. That also put the buildings in contact with a deep layer of permeable rock filled with water, mostly rain and melted snow from the nearby Abukuma Mountains, that flows to the Pacific.
The buildings managed to keep the water out until the accident on March 11, 2011. Either the natural disasters themselves, or the explosive meltdowns of three of the plant’s six reactors that followed, are believed to have cracked the buildings’ basements, allowing groundwater to pour in. Nearly 40,000 gallons of water a day keep flooding into the buildings.
Once inside, the water becomes highly radioactive, impeding efforts to eventually dismantle the plant. During the accident, the uranium fuel grew so hot that some of it is believed to have melted through the reactor’s steel floors and possibly into the basement underneath, though no one knows exactly where it lies. The continual flood of radioactive water has prevented engineers from searching for the fuel.
Since the accident, five robots sent into the reactor buildings have failed to return because of high radiation levels and obstruction from debris.
The water has also created a waste-management nightmare because Tepco must pump it out into holding tanks as quickly as it enters the buildings, to prevent it from overflowing into the Pacific. The company says that it has built more than 1,000 tanks that now hold more than 800,000 tons of radioactive water, enough to fill more than 320 Olympic-size swimming pools.
On a recent visit to the plant, workers were busily erecting more durable, welded tanks to replace the temporary ones thrown up in a hurry during the early years after the accident, some of which have leaked. Every available patch of space on the sprawling plant grounds now appears to be filled with 95-foot tanks.
“We have to escape from this cycle of ever more water building up inside the plant,” said Yuichi Okamura, a general manager of Tepco’s nuclear power division who guided a reporter through Fukushima Daiichi. About 7,000 workers are employed in the cleanup.
The ice wall is a high-technology bid to break that cycle by installing what might be the world’s largest freezer. Pipes almost 100 feet long have been sunk into the ground at roughly three-foot intervals, and filled with a brine solution supercooled to minus 30 degrees Celsius, or minus 22 Fahrenheit. Each pipe is supposed to freeze a column of soil about a foot and a half in radius, large enough to reach the ice column created by its neighboring pipes and form a seamless barrier.
Engineers with the wall’s builder, the construction giant Kajima Corp., estimate that it will take about two months for the soil around a pipe to fully freeze. Solidifying the entire wall, which consists of 1,568 such underground pipes, will require 30 large refrigeration units and consume enough electricity to light more than 13,000 Japanese homes for a year.
The technique of using frozen barriers to block groundwater has been used to build tunnels and mines around the world, but not on this scale. And certainly not on the site of a major nuclear disaster.
Since the start, the project has attracted its share of skeptics. Some say buried obstacles at the plant, including tunnels that linked the reactor buildings to other structures, will leave holes in the ice wall, making it more like a sieve. Others question why such an exotic solution is necessary when a traditional steel or concrete wall might perform better.
Some call the ice wall a flashy but desperate gambit to tame the water problem, after the government and Tepco were initially slow to address it. Adding to the urgency is the 2020 Olympics, which Prime Minister Shinzo Abe of Japan helped win for Tokyo three years ago by assuring the International Olympic Committee that the water troubles at Fukushima Daiichi were under control.
“It’s a Hail Mary play,” said Azby Brown, a Japan-based researcher for Safecast, an independent radiation-monitoring group. “Tepco underestimated the groundwater problem in the beginning, and now Japan is trying to catch up with a massive technical fix that is very expensive.”
Supporters and skeptics alike will soon learn if that gambit will succeed. After two years of work, Kajima finished installing the pipes and refrigerator units to create the ice wall in February. At the end of March, it switched on part of the ice wall for the first time — roughly half a mile that runs between the reactor buildings and the Pacific. Most of the other, uphill side of the wall was activated in mid-June.
Kajima is freezing the wall in stages under orders from the Nuclear Regulation Authority, Japan’s nuclear watchdog. The authority is concerned that cutting off the groundwater too suddenly might lead to a reversal of flows, causing the radioactive water accumulated inside the reactor buildings to start pouring out into the surrounding soil, possibly reaching the Pacific. It has told Kajima to leave a half-dozen “gateways” in the uphill side that will not be closed until much of the contaminated water is drained from the buildings.
This month, Tepco told the nuclear agency that the seaside segment of the ice wall had frozen about 99 percent solid. It says a few spots have failed to solidify because they contain buried rubble or sand left from the plant’s construction a half-century ago, which now allow groundwater to flow through so quickly that it will not freeze.
Tatsuhiro Yamagishi, a spokesman for Tepco, said the company was trying to plug these holes in the ice wall with quick-drying cement. “We have started to see some progress in temperature decrease,” he said.
Even if the cement helps make the ice wall watertight, skeptics question how long it can last. They point out that such frozen barriers are usually temporary against groundwater at construction sites. They say the brine solution used to chill the pipes is highly corrosive, which could make them break or leak. It is also unclear whether the system could break down under the stresses of operating in a high-radiation environment where another earthquake could lead to another power loss.
“Why build such an elaborate and fragile wall when there is a more permanent solution available?” said Sumio Mabuchi, a former construction minister who has called for building a slurry wall, a trench filled with liquid concrete that is commonly used to block water.
Isao Abe, a Kajima engineer overseeing the ice wall, said his company had made the wall more durable by installing underground pipes that are easy to replace if they corrode. He also said the ice wall was self-sealing, meaning that if another earthquake caused cracks, any incoming water would freeze right away, restoring the wall. He also said it would take months for the wall to thaw, giving engineers ample time to restore power even if the plant has another outage.
Mr. Abe said the wall was intended to operate until 2021, giving Tepco five more years to find and plug the holes in the reactor buildings, though skeptics say this difficult task will require more time. Mr. Abe also pointed out that the ice wall was part of a broader strategy for containing the radioactive water. Before installing the ice wall, Kajima also built a conventional steel wall underground along the plant’s border with the Pacific last year.
Tepco says that wall has already stopped all measurable leaks of radioactive materials into the sea. However, some scientists say that radioactive water may still be seeping through layers of permeable rock that lie deep below the plant, emptying into the Pacific far offshore. They say the only way to eliminate all leaks would be to repair the buildings once and for all.
Even if the ice wall works, Tepco will face the herculean task of dealing with the huge amounts of contaminated water that have accumulated. The company has installed filtering systems that can remove all nuclear particles but one, a radioactive form of hydrogen known as tritium. The central government and Tepco have yet to figure out what to do with the tritium-laced water; proposals to dilute and dump it into the Pacific have met with resistance from local fishermen, and risk an international backlash.
For now, the only visible sign that the freezing has begun are silver-dollar-size patches of ice that have formed on top of the aboveground, silver pipes. At one spot, the No. 4 reactor building loomed, an enormous cube six stories tall with concrete sides that showed large gashes left by the tsunami.
“The water is here, just three meters beneath our feet,” said Mr. Okamura, the Tepco general manager, who stood near the pipes wearing a white protective suit, goggles and a surgical mask. “It still flows into the building, unseen, without stopping.”