22 Août 2013
Aug. 21, 2013
Several hundred tons of radioactive water that leaked from a storage tank at Tokyo Electric Power Co.’s crippled Fukushima No. 1 nuclear plant may have flowed to the sea, Tepco admitted Wednesday, adding that it is “hurriedly checking” to learn if 350 similar tanks are also leaking.
Tepco is desperately trying to seal the tank, which has leaked about 300 tons of radioactive water. The tank, considered temporary, is made of steel plates bolted together with sealed seams. Tepco is also using more durable welded tanks to store the highly radioactive water, which is accumulating daily.
The water was used to cool the three melted reactors, then stored for later possible decontamination. So far, Tepco has built more than 1,000 tanks on site.
Spokesman Tsuyoshi Numajiri said traces of radioactivity were detected in a drainage stream.
“There is a possibility that earth and sand contaminated with the leaked water flowed into the drainage. We cannot rule out the possibility that part of the contaminated water flowed into the sea,” he said.
“We intend to make detailed examinations.”
A Tepco official said earlier Wednesday the tank was believed to still be leaking but the utility has yet to pinpoint where the hole is. The water is apparently being absorbed into the ground and possibly mixing with the groundwater that flows under the stricken plant.
Tepco was also desperately trying to determine if 350 similar temporary tanks at the plant were also leaking.
Numajiri said workers are removing soil contaminated by the leaked water, and pumping the remaining water from the leaky tank.
He said there were no significant changes in radiation levels outside the plant.
An earthquake-generated tsunami knocked out reactor cooling systems and sparked the three meltdowns at the plant in March 2011, in the worst nuclear plant calamity since Chernobyl in 1986.
Water contaminated with an estimated 30 trillion becquerels of radioactive substances is highly likely to have leaked directly into the sea from the premises of the tsunami-hit Fukushima No. 1 Nuclear Power Plant, its operator announced on Aug. 22.
Tokyo Electric Power Co. (TEPCO) officials explained that the water that had accumulated in underground tunnels in the power station's No. 2 and 3 reactors since shortly after the March 2011 accident is likely to be leaking into the sea.
The utility estimates that the water it believes has already flowed into the sea was contaminated with up to 10 trillion becquerels of strontium-90 and up to 20 trillion becquerels of cesium-137. The two radioactive substances could total 30 trillion becquerels, more than 100 times the upper limit on the amount of such substances that can be released into the sea per year, which is set at 220 billion becquerels.
TEPCO made the estimation from the density of radioactive substances detected in the port and harbor facility on the premise of the power station on the assumption that the water has been leaking into the sea since May 2011.
The utility had previously explained that underground water that was contaminated after getting mixed with radioactive water was leaking. However, since such a large amount of radioactive substances is highly unlikely to be released from underground water alone, TEPCO came to the conclusion that highly contaminated water is likely to be leaking directly into the sea from the underground tunnels for the No. 2 and 3 reactors through a crushed stone stratum.
The power company plans to pump up highly radioactive water from the underground tunnels and remove cesium and other radioactive substances in the plant's water treatment facility. Treated water will be stored in above-ground tanks.
On Aug. 2, TEPCO released its estimate that underground water contaminated with up to 40 trillion becquerels of tritium had leaked into the sea from the compounds of the crippled power station.
TOKYO (Kyodo) -- Highly radioactive water that leaked from a storage tank at the Fukushima Daiichi nuclear power plant could have flowed into the adjacent Pacific Ocean through drainage channels, data provided by Tokyo Electric Power Co. showed Wednesday.
TEPCO is studying the possibility in detail, Executive Vice President Zengo Aizawa told a press conference.
TEPCO first noticed on Monday puddles with high radiation levels near an area where many storage tanks stand. The seriousness of the situation escalated when the utility later found that 300 tons of toxic water had likely leaked from a tank that should have been holding about 1,000 tons.
The Nuclear Regulation Authority said Wednesday it is considering raising the severity assessment of the event to level 3 on an eight-point international scale from level 1.
Level 3 on the International Nuclear and Radiological Event Scale is defined as a "serious incident." The Fukushima nuclear accident, triggered by a huge earthquake and tsunami in March 2011, has been rated as the maximum level 7, on a par with the 1986 Chernobyl disaster.
The NRA hopes to reach a conclusion on the issue after consulting with the International Atomic Energy Agency on whether it is appropriate to apply the so-called INES scale to an incident at facilities set up to deal with a nuclear crisis that has still not come to an end.
TEPCO has still not been able to determine from where in the tank the radioactive water is escaping. The container is 12 meters in diameter and 11 meters high, built of steel plates held together by bolts.
TEPCO has collected 4 tons of the leaked water, and said most of the remaining water likely seeped into the ground.
But TEPCO also said Wednesday it detected 6 millisieverts per hour of radiation inside a drainage channel not far from the tank, possibly indicating some of the leaked water entered the gutter.
The channel connects to another drainage channel which leads to the sea.
However if any toxic water did flow into the sea, confirming that fact would be difficult once it mixed with seawater.
A seawater sample taken near the drainage channel outlet contained a small amount of radioactive cesium-137, but the density of radioactive substances emitting beta rays was at an undetectable level.
A low concrete wall exists near the tanks to prevent leaked water from spreading, but TEPCO left open drain valves attached to the wall, thinking that would make it easier to detect leaks.
The valves are now closed. TEPCO also finished transferring the water that was left inside the troubled tank to other tanks nearby by Wednesday night.
Several types of tanks are used at the Fukushima plant to store a massive volume of radioactive water resulting from the continuing injection of water into the three reactors that suffered meltdowns. Some 300 are the same type as the one found to have leaked.
The situation is arousing concern in neighboring countries such as China and South Korea. Those two countries have requested Japan provide detail information about the issue.
Tokyo Electric Power Co. calculated that up to 10 trillion becquerels of radioactive strontium and 20 trillion becquerels of cesium 137 were in contaminated water from the stricken Fukushima No. 1 nuclear power plant that flowed into the sea since the outset of the disaster.
TEPCO released the results of calculations on Aug. 21. The figures for both radioactive elements are more than 100 times the managed emissions of 220 billion becquerels over the course of one year of normal operations at the nuclear plant.
However, TEPCO officials said the calculated estimates were still below the central government's standards.
Based on the concentration of radioactive materials found in seawater within the port by the nuclear plant, estimates were made that between 3 billion and 10 billion becquerels of strontium flowed into the ocean daily, while between 4 billion and 20 billion becquerels of cesium 137 flowed into the ocean.
On the assumption that contaminated water mixed with groundwater and flowed into the ocean from May 2011, soon after the nuclear crisis unfolded, the estimates represent the maximum amounts of strontium and cesium that might have flowed into the ocean.
The plant was wrecked by the March 11, 2011, Great East Japan Earthquake and tsunami.