LEVELS of radioactivity have risen sharply in seawater near a tsunami-crippled nuclear plant in northern Japan, possibly signalling new leaks at the facility, the government said.
The announcement came after a magnitude-5.9 earthquake jolted Japan this 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 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 yesterday, up from 1100 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 on 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 said.
However, the increase in iodine-131, which has a relatively short eight-day half life, could signal a new leak, he said.
“We want to determine the origin and contain the leak but I must admit that tracking it down is difficult,” he said.
TEPCO also said it had started dumping a mineral into the sea that absorbs radioactive substances, aiming to slow down contamination of the ocean.
The company began dropping zeolite near a water outlet from the Fukushima Daiichi plant – which has been leaking radiation since it was crippled by a March 11 quake and tsunami – from yesterday.
The mineral has wide-ranging industrial applications, including nuclear waste processing.
Officials hope it will help to reduce the spread of radioactive materials from the plant into the Pacific, although the effectiveness of the measure was not yet clear.
The mineral has been used to help mitigate other nuclear accidents, including the 1979 Three Mile Island nuclear accident in the United States.