TOKYO—Japan's nuclear regulator said it was moving tons of contaminated water after detecting signs of leakage from one of seven underground pools at the tsunami-crippled Fukushima Daiichi nuclear-power plant.
The country's Nuclear Regulation Authority said Saturday that up to 120 metric tons of contaminated water may have leaked into nearby soil surrounding the plant but that the leak is unlikely to have reached the sea, half a mile (800 meters) from the cooling pool.
To prevent another leak, plant operator Tokyo Electric Power Co. 9501.TO +1.02% started pumping water from the suspect pool to an adjacent one early Saturday, the NRA said in a statement.
The transfer of the water will take about three days to complete, the NRA said. The pool is almost 200 feet long (60 meters), 173 feet wide and 20 feet deep, and is lined with three layers of waterproof sheets. About 13,000 tons of contaminated water remaining in the pool are being emptied.
According to the NRA, radioactive substances were detected in the soil immediately surrounding the pool.
TEPCO detected the leak earlier in the week, when radiation levels spiked in water samples collected in between the inner linings of the tank. Radiation levels in water samples taken outside the tank also have increased, an indication of the water leak, TEPCO spokesman Masayuki Ono told the Associated Press.
An increasing amount of water is being stored at the Fukushima plant after being used to keep reactors and spent fuel cool. Radioactive cesium is removed from the water after use, but other radioactive substances remain in it.
The leak isn't only an immediate environmental concern, but threatens TEPCO's tight water management situation, Mr. Ono said, according to the AP. So much water has been used that TEPCO is struggling to find storage space.
"The impact (from the leak) isn't small, as the space is already tight," Mr. Ono said. "We need to revise our water management plans."