Radiation readings near water tanks at the crippled Fukushima nuclear power plant have risen dramatically, with one test registering lethal levels, the plant's operators reported Sunday.
The Tokyo Electric Power Co., or TEPCO, said the high readings were discovered at four new locations on Saturday, near the joints at the bottom of storage tanks that are holding highly contaminated water. One of the readings reached 1,800 millisieverts per hour, which is considered enough to kill an exposed person in four hours, the company said. Previous readings around the same tank registered a dose of 100 millisieverts per hour.
Other locations registered readings that ranged from 70 to 230 millisieverts, TEPCO said. The typical American receives a background radiation dose of 6.2 millisieverts per year, and Japanese law sets an annual exposure limit of 50 millisieverts for nuclear plant workers during normal hours.
Radioactive water is being stored in hundreds of tanks at the Fukushima site, in the wake of the plant's catastrophic failure in 2011 during Japan's magnitude-9 earthquake and tsunami. Additional contaminated groundwater is being pumped into the tanks from the plant's ruins every day. Last month, TEPCO said 300 tons of water was found leaking from one of the tanks. That prompted nuclear regulators in Japan to classify the leak's severity as a Level 3 "serious incident" on the international scale for radiation releases.
TEPCO has increased its surveillance of the facility and says it will begin removing the contaminated soil around the storage tanks. On Sunday, the company said inspectors have not detected any significant changes in the water level inside the vessels where the latest readings were taken. That led them to believe that the newly detected contamination has not spread beyond the concrete barriers surrounding the tanks.
A TEPCO spokesman told Reuters that "we are investigating the cause" of the rise in radiation levels. He said one factor behind the higher readings was that investigators used an instrument capable of registering greater amounts of radiation. Instruments used previously had been capable of measuring radiation only up to 100 millisieverts, but the new instruments were able to measure up to 10,000 millisieverts, the spokesman told Reuters.
The company said the radiation measured was beta rays, which would be easier to protect against than gamma rays.