The recent leaking of radioactive water from a storage tank at the Fukushima No. 1 nuclear plant--and the suspected leak from a second tank--illustrate the plant operator’s challenge in safely disposing of increasing amounts of contaminated water, with no effective solution in sight.
Tokyo Electric Power Co. said April 7 that it suspects a new smaller leak separate from the one that it confirmed the day before of about 120 tons of contaminated water from an underground storage tank at the nuclear complex. In a news conference, the utility said that it detected a small amount of radioactive materials outside the second tank, which is adjacent to the first leaking one.
In a news conference early on the day before, Masayuki Ono, a TEPCO spokesman, explained how the leak occurred in the first tank.
“Sheets made of polyethylene have lost the ability of retaining water and a small amount (of contaminated water) has leaked outside,” Ono said.
On April 3, the utility detected radioactive materials in underground water surrounding the storage tank.
But the company waited two days before reporting it to the government.
“We believed a detailed investigation (of the situation) was needed (before reporting it to authorities),” Ono said, explaining the delay.
The amount of leaked water was estimated at 120 tons. Although TEPCO denied that all of it leaked outside, the leak was the largest since the government declared in December 2011, nine months after the crisis unfolded at the nuclear complex, that the disaster was under control.
The underground storage tank--60 meters long, 53 meters wide and 6 meters deep--is lined with an outer 6.4 millimeter-thick layer of clay, and topped by two layers of polyethylene sheets, each 1.5 millimeters thick.
Ono said the exact cause of the leak has yet to be determined, and that a detailed investigation will follow after all of the contaminated water at the leaking tank was removed.
“There is the possibility that joints in the water-shielding sheets have been damaged,” he said. “The sheets turned out not to have the ability they were designed for.”
TEPCO began transferring contaminated water from the leaky tank to two nearby underground tanks with similar seepage control methods in place. Seven underground storage tanks have been built, and so far, five of these tanks have been used to hold contaminated water.
Asked about the potential of new leaks occurring in the other tanks, Ono said, “The possibility that leaks may occur again is not zero, but (transferring contaminated water to the nearby tanks) is the best possible step we can take.”
The transfer is expected to be completed early this week, by when up to an additional 47 tons of polluted water is projected to have leaked.
On April 6, TEPCO detected a tiny amount of radioactive substance in groundwater around the two storage tanks adjacent to the leaky tank.
The utility will monitor radiation levels in the coming weeks.
On April 7, in the second suspected leak, the utility said water found between the sheets in another underground tank measured 2,200 becquerels of radioactivity per cubic centimeter. The water level in the tank had not dropped, so the amount of leakage is considered small, TEPCO said.
The utility is injecting about 370 tons of water a day to cool the melted nuclear fuel at the crippled plant's No. 1-3 reactors.
TEPCO has been removing radioactive cesium from the contaminated water that was used to cool the reactors.
Some of this contaminated water was recycled as cooling water. The remainder is stored in the tanks before it is treated to reduce radiation levels.
The overall volume of contaminated water on the nuclear complex is rising steadily, partly because 400 tons of groundwater a day is flowing into the reactor buildings.
TEPCO plans to pump out the groundwater, but the company said it is impossible to prevent the entire influx.
Even if the project to pump out groundwater goes as envisaged, the plant would be still left with 200-300 tons of groundwater flowing in daily.
The company has built tanks to hold increasing amounts of contaminated water in the forest area on the premises.
But the storage capacity of these facilities is nearing their limits, TEPCO said. The tanks have a capacity of storing 325,000 tons, and 80 percent of those tanks were already filled.
As of April 2, the amount of contaminated water at the plant is estimated at 370,000 tons, including the figure for highly radioactive water remaining in the basements of the reactor buildings.
TEPCO plans to expand the capacity of storing polluted water to 450,000 tons by autumn. In addition, it is considering building tanks to hold an additional 250,000 tons of contaminated water.
Still, the tanks will be filled within several years. The tank that was found to be leaking is also no longer usable, depriving the plant of 14,000 tons of capacity.
Acknowledging the loss, TEPCO said in its April 6 news conference it has to rework its long-term plan for dealing with contaminated water.
The utility began a trial run of Alps, a new apparatus to treat contaminated water, in late March. If Alps goes into full operation, the system is supposed to significantly reduce radiation levels, as it is capable of removing most radioactive materials, including strontium. Contaminated water contains strontium after cesium is removed.
Still, TEPCO will have to find a final destination for the contaminated water after treating it. One option, discharging treated water into the sea, is strongly opposed by local fishermen.
(This article was written by Shunsuke Kimura and Jin Nishikawa.)
- « Prev
- Next »