See extensive graphic of Fukushima plant situation here
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Even geography is working against Tokyo Electric Power Co. and the government in their struggle to deal with the persistent problem of radiation-contaminated water at the Fukushima No. 1 nuclear plant.
The site receives so much groundwater that special equipment--rendered useless by the 2011 earthquake and tsunami--was set up to prevent the plant’s buildings from floating on the continuous flow.
The most pressing problem is stopping the groundwater from entering the plant’s reactor buildings, becoming contaminated and spilling into the sea. But it is far from the only obstacle in the roadmap to decommission the reactors at the stricken plant.
TEPCO still does not know all the details of how and where groundwater is entering the buildings. Also in the dark about the full extent of the problem, the central government has stepped in and is resorting to unprecedented measures with potential pitfalls.
An estimated 800 to 1,000 tons of groundwater flows daily in the direction of the Fukushima plant buildings, a volume much larger than those at other nuclear plants.
The original site of the Fukushima No. 1 plant was a cliff more than 30 meters high. But 20 meters was lopped off to create the foundation of the nuclear plant, putting the groundwater level only a few meters below the surface.
The plant itself was constructed on land containing gravel layers through which water can easily pass through. In the past, a brook trickled by the No. 4 reactor.
According to Atsunao Marui, who heads the Groundwater Research Group at the National Institute of Advanced Industrial Science and Technology, rain makes up most of the groundwater at the Fukushima plant. Water also flows in from the Abukuma Highlands.
“About 4 million tons of rain falls on the plant site over the course of a year,” Marui said. “Of that figure, it is believed that between 1 million and 1.5 million tons seep into the ground.”
Subdrains at depths of between 10 and 15 meters were constructed around the reactor buildings to pump up groundwater and send it out to sea. Without that pumping, the buildings faced the danger of being buoyed by rising groundwater.
The subdrains could pump up 850 to 1,200 tons of groundwater a day, enough to fill three to four 25-meter swimming pools.
But the subdrains were rendered inoperable after the Great East Japan Earthquake and tsunami knocked out power to the plant on March 11, 2011, leading to the meltdowns of three reactors.
Now, about 400 tons of groundwater flows daily into the buildings for the No. 1 to 4 reactors and mixes with water already contaminated by the melted nuclear fuel.
The growing volume of contaminated water continues to be stored in tanks installed on the plant site. As of Sept. 10, 435,000 tons of polluted water was held in building basements and tanks, an increase of 137,000 tons over the course of a year.
TEPCO officials have pinpointed only two locations, including the turbine building of the No. 1 reactor, where groundwater is entering the building basements. They believe there are many more breaches.
However, workers have been unable to confirm such locations and plug the holes because dangerous radiation levels make it difficult to approach the trouble spots.
Highly radioactive water in the building basements is also flowing into underground trenches that hold cables and other equipment. Some of that contaminated water is believed to be leaking into the ground, mixing with groundwater and heading toward the ocean.
Industry ministry officials estimate that 300 tons of such radioactive water flows into the ocean daily.
Faced with the continuing water problems at the site, the central government decided to take a more active role in dealing with the situation.
The Nuclear Emergency Response Headquarters on Sept. 3 released a plan that includes a two-phase approach to deal with the contaminated water: emergency steps to be implemented immediately, and comprehensive measures that would be carried out over the next year or two.
The first emergency measure is removing about 20,000 tons of highly radioactive water accumulated in the underground trenches toward the ocean side of the reactor buildings to prevent it from flowing into the sea.
But the trenches are connected to the turbine buildings, so additional contaminated water would fill the trenches even if water is pumped up.
The government plans to stop water from entering or exiting the trenches by the end of the current fiscal year. To achieve that goal, one measure being considered is freezing the water in the connecting joints to the trenches. However, that work could be difficult considering the high water pressure involved.
Another emergency measure is establishing a groundwater bypass from wells toward the mountain side of the reactor buildings to divert the water to the ocean before it becomes contaminated. Construction on 12 of those wells as well as the piping was completed in March. Once the system begins operations, the volume of water flowing into the buildings could be reduced by about 100 tons daily.
However, local communities distrustful of TEPCO have still not given their consent to having the water dumped into the ocean.
“The only thing to do with water that is not dangerous is to release it,” said Osamu Tochiyama, a former professor of nuclear engineering at Tohoku University. “Rather than leave matters up to TEPCO, the central government should have shown that it was responding to the negative publicity that had arisen from the nuclear accident. It should have provided support to ensure that the problem was being dealt with in a more assuring manner.”
A key part of the government’s plan is building a 1,400-meter-long underground wall of frozen soil that would surround the area holding the No. 1 to 4 reactors. The central government plans to earmark 32 billion yen ($322 million) in construction costs for the wall, and it is seeking to start the project in fiscal 2014.
According to the plan, the frozen wall would prevent groundwater from entering the buildings, allowing workers to remove the contaminated water there.
The frozen soil wall technology has been used in tunnel construction. But there is no precedent for the scale of what would be needed at the Fukushima plant.
Another comprehensive measure will be restarting the subdrains to lower the groundwater level, thereby reducing the volume of contaminated water within the buildings. The government is seeking to resume subdrain operations in September 2014.
The function of the frozen soil wall would end after groundwater no longer leaked into the buildings. According to the plan, contaminated water could then be removed and water circulated within the buildings to cool the melted fuel.
But it would still not represent an end to all the problems at the Fukushima nuclear plant.
For example, the tanks on the plant site would continue to hold huge amounts of contaminated water.
TEPCO is seeking an early start of operations of the Alps multi-nuclide removal equipment, which can eliminate 62 radioactive substances from contaminated water. Reducing the amount of such substances would reduce the risk in the event contaminated water leaked from the tanks.
However, that would still leave open the question of what to do about tritium, a radioactive isotope of hydrogen that cannot be removed by the Alps equipment.
(This article was written by Shunsuke Kimura, Ryuta Koike and Senior Staff Writer Hisashi Hattori.)
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