In the center from the top are the buildings housing the No. 1, No. 2, No. 3 and No. 4 reactors at the Fukushima No. 1 nuclear power plant. (Provided by Air Photo Service)Editor's note: We will update our earthquake news as frequently as possible on AJW's Facebook page: http://www.facebook.com/AJW.Asahi. Please check the latest developments in this disaster. From Toshio Jo, managing editor, International Division, The Asahi Shimbun.
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The density of iodine-131 in seawater 330 meters south of an outlet at the quake-stricken Fukushima No. 1 nuclear power plant shot up to 3,355 times the acceptable limit on Tuesday, Tokyo Electric Power Co. said Wednesday.
It also said the density level 30 meters to the north of another outlet at the plant soared to 1,263 times.
While a heroic effort is being made to bring the crippled reactors at the plant under control, officials and experts are closely watching how leaking radioactive substances will contaminate the sea and affect marine life.
In the plant compound, highly radioactive water has been quickly filling up trenches outside the reactor buildings, fueling concerns that voluminous amounts of contaminated water may flow into the sea.
"We must prevent the polluted water from flowing into the sea, but because it will be diffused by sea currents, it will not have an immediate impact on neighborhood residents," said Hidehiko Nishiyama, a spokesman for the Nuclear and Industrial Safety Agency.
Experts suspect the radioactive substances may be leaking from melted nuclear fuel in reactor cores.
Examinations of nearby seawater by TEPCO, the plant's operator, had turned up radioactive iodine, cesium and barium in much higher densities than normal.
The iodine levels had temporarily fallen on Monday after marking much higher than normal readings late last week. The density of cesium-134 and cesium-137 also rose on Tuesday.
Keiji Kobayashi, a former lecturer of nuclear engineering at Kyoto University's Research Reactor Institute, says those materials must have leaked into the sea from reactor cores.
"Given the types and densities of radioactive materials found, a predominant portion should have come in water contaminated by melted fuel in a reactor core, rather than being spewed into the air and coming down in rain," he said.
The utility said it has not determined where the leak originated, but officials suspect the culprit is fuel in reactor cores.
In the trench for pipes and electrical wires connected to the turbine building for the No. 2 reactor, water showed a high reading of 300 millisieverts of radiation per hour.
Officials suspect the trenches at the plant, with a total capacity of 13,300 tons, were filled almost to capacity with polluted water.
Water is still being pumped into the reactor to cool fuel rods. If water continues to flow into the trench, it could spill out into the sea in large quantities and contaminate the immediate area.
Some fear radioactive water may have already seeped out.
"It is difficult to imagine how much polluted water may flow into the sea," Kobayashi said. "In the case of the No. 2 reactor, where the suppression pool connected to the core containment vessel may have been damaged, it is possible a hole has appeared at a welded joint or a tube in measuring equipment."
The radioactivity figures far offshore were much smaller and coming down as of Monday, according to the science ministry.
But TEPCO reported that the level of iodine-131 was 59 times the acceptable limit at a beach 16 kilometers south of the plant on Monday morning.
Hideyuki Koyama, a former lecturer of engineering at Osaka Prefecture University who now leads an anti-nuclear power group, called for strict monitoring of sea pollution.
"The state and TEPCO say the levels are only temporarily high and that there is no need to worry because radioactivity will be dispersed in the sea, but it is not necessarily the case," he said.
Experts say it is difficult to predict how radioactive substances will spread in the sea as the combined effects of sea currents, wind and water temperatures affect dispersion.
How radioactive materials are concentrated and accumulated in fish also depends upon a variety of conditions in the natural world, according to Kenya Mizuguchi, a professor emeritus of resources management at the Tokyo University of Marine Science and Technology.
Because iodine-131 has a short half-life of eight days, there is little concern that fish will become unedible due to high levels of contamination from iodine.
Takami Morita, a researcher of marine chemistry at the Fisheries Agency, also said cesium will have no major impact on marine life.
According to Morita, half of cesium absorbed by fish will be discharged in 50 days.
"Compared with other chemicals, the rate of its concentration is low, and it is also hard to accumulate," he said.
"Furthermore, cesium accumulated on the seabed attaches itself to sediments and will not be dissolved again in the water. So it will not greatly affect fish and other marine life."
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