The levels of the radioactive element were low enough that they should not pose a significant health risk, said Sakae Muto, vice president of Tokyo Electric Power Co.
Workers at the Daiichi plant are trying to fully restore power, needed to cycle cool water around nuclear fuel rods and keep them from overheating, and Japanese national broadcaster NHK reported that the soil finding will not require work to stop.
Officials also said Monday that dangerously radioactive water had been found a day earlier four inches below ground level in one tunnel. They are concerned that it could overflow and spread into the soil or out to sea, less than 200 feet away.
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 for thousands of years.
Company officials said plutonium in two of the five soil samples may be linked to the recent accident. The others could be the result of nuclear fallout; trace amounts of plutonium were found around the world after nuclear weapons tests a half-century ago.
Radiation levels found in the tunnels, meanwhile, were similar to those found in water that has pooled in turbine rooms adjacent to three of the six nuclear reactors in the Daiichi plant. The highest levels, measuring at more than 1,000 millisieverts per hour, were found outside the second reactor. Such a high reading would deliver a year’s radiation dose legally permitted in an emergency in just 15 minutes. 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 government spokesman, Yukio Edano, called the discovery of contaminated water outside concrete buildings designed to seal off contamination “regrettable.” He told reporters that the government “will do everything it can to bring the problems under control” and “to minimize the impact on human health.”
In the United States, opponents of MOX fuel — which is made from reprocessed nuclear weapons — seized on the report of leaking plutonium to question plans to use the fuel here. Rep. Edward J. Markey (D-Mass.) called for “an immediate safety review” of plans to use MOX at power plants in Alabama, Tennessee and Washington state.
Gregory Jaczko, the chairman of the U.S. Nuclear Regulatory Commission, traveled to Tokyo on Monday to support the work at the badly damaged plant. “The unprecedented challenge before us remains serious, and our best experts remain fully engaged to help Japan address the situation,” he said in a statement issued by the U.S. Embassy.