TOKYO — Levels of radioactivity have risen sharply in seawater near a tsunami-crippled nuclear plant in northern Japan, possibly signaling new leaks at the facility, the government said Saturday.
The announcement came after a magnitude-5.9 earthquake jolted Japan on Saturday morning, hours after the country's nuclear safety agency ordered plant operators to beef up their quake preparedness systems to prevent a recurrence of the nuclear crisis.
There were no immediate reports of damage from the earthquake, and there was no risk of a tsunami similar to the one last month that crippled the Fukushima Dai-ichi nuclear plant, causing Japan's worst-ever nuclear plant disaster. Japan has been hit by a string of smaller quakes since the magnitude-9.0 earthquake hit the country March 11.
Since the tsunami flooded the Fukushima plant and knocked out cooling systems, workers have been spraying massive amounts of water to cool the overheated reactors. Some of that water, contaminated with radiation, had leaked into the Pacific. Plant officials said they plugged that leak on April 5 and radiation levels in the sea dropped.
But the government said Saturday that radioactivity in the seawater has risen again in recent days. The level of radioactive iodine-131 spiked to 6,500 times the legal limit, according to samples taken Friday, up from 1,100 times the limit in samples taken the day before. Levels of cesium-134 and cesium-137 rose nearly fourfold. The increased levels are still far below those recorded earlier this month before the initial leak was plugged.
The new rise in radioactivity could have been caused by the installation Friday of steel panels intended to contain radiation which may have temporarily stirred up stagnant waste in the area, Hidehiko Nishiyama of the Nuclear and Industrial Safety Agency told reporters. However, the increase in iodine-131, which has a relatively short eight-day half life, could signal the possibility of a new leak, he said.