Attempts to contain and eliminate highly irradiated water at the embattled Fukushima Dai-Ichi power plant stumbled Monday when contaminated water was reported in three underground tunnels outside the nuclear reactors.
Officials said Monday afternoon that dangerously radioactive water had been found a day earlier just 4 inches below ground level in one tunnel, and government officials were concerned it would overflow and spread into the soil or out to sea, less than 200 feet away.
Tokyo Electric Power Co., which owns the plant, also found small amounts of plutonium in the soil around the plant, company officials said late Monday night. The levels of the radioactive element, found in two out of five samples taken March 21 and 22, were low enough that they should not pose a significant health risk, officials said, according to Japanese national broadcaster NHK. The finding will not require stopping work at the plant, NHK reported.
Plutonium is produced as a byproduct of uranium fission; it is also an ingredient in the mixed oxide fuel, known as MOX, that has been used in the plant's third reactor. If inhaled, plutonium can cause cancer in the lungs or other organs or bones. It has an extremely long half-life, meaning it will linger thousands of years.
Radiation levels found in the water in the underground tunnels were similar to those found in contaminated water that has pooled in turbine rooms adjacent to three of the six nuclear reactors in the Dai-Ichi plant. The highest levels, measuring at over 1,000 millisieverts per hour (or more than four times the legal exposure limit for nuclear workers), were found outside the second reactor. The levels in the other two tunnels were much lower.
Water that has leaked into the turbine room in the second reactor probably came into contact with partially melted nuclear fuel rods, Japan's nuclear safety agency reported Monday. Workers are still trying to determine how the water leaked out.
Japan's chief Cabinet secretary, Yokio Edano, called the discovery of contaminated water outside concrete buildings designed to seal off contamination "regrettable." He said at a news conference that the government "will do everything it can to bring the problems under control" and "to minimize the impact on human health."
The spreading contamination represents a critical safety concern for workers at the plant and will mean further delays to fully restoring power needed to cycle cool water around the fuel rods and keep them from overheating.
The hazardous water was first discovered outside reactors Thursday when three workers were hospitalized after suffering radiation burns in the turbine room of the second reactor. The workers were released Monday, and doctors said they had no internal injuries or skin abnormalities.
As power company officials investigate the source of the leaks, the amount of water being injected into the second reactor Monday was reduced from 9 tons to 7 tons, according to Japanese news reports.
The reduction might limit flooding, but it could also increase the risk that the fuel rods will overheat.
The additional contaminated water complicates an already difficult cleanup job. The stagnant water still has not been drained from the turbine buildings, Hidehiko Nishiyama, deputy-general for the government's Nuclear and Industrial Safety Agency, said in a news conference. A pump has been placed in the first building, he said, but in the second two, "we are considering what to do."
He added, "We need to make a decision and act as soon as possible."
At the same time, radioactive water was measured in the sea surrounding the plant for the third consecutive day. The levels of iodine-131 in water sampled Sunday were 1,150 times greater than government-set safety levels.
Since March 15, doctors at the National Institute of Radiological Sciences have screened 862 workers and 230 residents who live within nearly two miles of the Dai-Ichi complex. So far, none has been found to have dangerously high levels of radiation, said Bummei Nakayama, a physician who helped with the screening.