A magnitude 7.1 aftershock struck off the coast of northeast Japan on Monday as the Japanese government said it was preparing to expand the evacuation zone around a crippled Fukushima nuclear power plant to address concerns over long-term exposure to radiation.
Authorities issued a warning for a three feet high tsunami after today’s earthquake, which had its epicentre in Fukushima prefecture. The warning was lifted after an hour. NHK state television said it caused the off-site power supply for two damaged reactors to shut down.
An official for the operator of the Fukushima plant, Tokyo Electric Power Company, said a temporary loss of external power at the plant following the aftershock had briefly knocked out pumps sending water into the facility’s three most severely damaged reactors.
Monday’s aftershock took place farther south than earlier ones, and was the most powerful recorded between Fukushima and Tokyo. The epicenter of the latest event was 50 miles south of Fukushima and 101 miles north-northeast of Tokyo.
Earlier Monday, thousands bowed their heads in silence to mark the one-month anniversary of the 9.1-magnitude earthquake and ensuing tsunami that brought widespread destruction to a wide swath of Japan’s northeast Pacific coast and triggered a nuclear crisis.
Chief Cabinet Secretary Yukio Edano said villages and towns outside the 20 km evacuation zone that have had more accumulated radiation would be evacuated. Children, pregnant women, and hospitalised patients should stay out of some areas 20-30 km from the Fukushima nuclear complex, he said.
These areas are feared to be receiving exposure to radiation equivalent to at least 20 millisieverts a year, which could be harmful to human health over the long term. Evacuation orders will come within a month, Mr. Edano added.
Five other areas may be told to evacuate if there is a worsening of the crisis at the Fukushima Daiichi station, which was severely damaged in the March 11 tsunami, said Mr. Edano.
“These new evacuation plans are meant to ensure safety against risks of living there for half a year or one year,” he said. There was no need to evacuate immediately, he added.
The Japanese government had so far refused to widen the zone, despite being urged to do so by the International Atomic Energy Agency, and countries such as the U.S. and Australia advised their citizens to stay 50 miles away from the plant.
Michael Friedlander, a former senior nuclear plant operator for 13 years in the U.S., said that the Japanese decision to evacuate a wider area made sense not just in terms of protecting people in these areas, but also in terms of making easier the eventual decontamination of farms and communities.
Allowing people and non-emergency vehicles to continue moving through radiation-contaminated areas and safer areas on the outskirts of the Fukushima Daiichi reactors runs the risk of spreading around radioactively contaminated particles, which could result in more square miles of territory being contaminated.
The I.A.E.A., based in Vienna, said on Sunday that its team had measured radiation on Saturday of 0.4 to 3.7 microsieverts per hour at distances of 20 to 40 miles from the damaged nuclear reactors — well outside the earlier evacuation zone. At that rate of accumulation, it would take to 225 days to 5.7 years to reach the Japanese government’s cutoff of evacuating areas where radiation is accumulating at a rate of at least 20 millisieverts per year.
Engineers at the damaged Daiichi plant north of Tokyo said they were no closer to restoring the plant’s cooling system which is critical if overheated fuel rods are to be cooled and the six reactors brought under control.
Though airborne radiation levels around the plant have come down in recent weeks, the plant has been battling to contain leaks of highly radioactive water from the facility.
The plant’s operator, Tokyo Electric Power Company, has pumped water into the reactors to cool the nuclear fuel rods, but that has produced harmful runoff of at least 60,000 tons of contaminated water and workers have been forced to pump lower-level radioactive water into the Pacific Ocean.
The death toll from the disaster, Japan’s worst since World War II, has surpassed 12,596, with more than 14,747 people still missing, according to Japan’s National Police Agency. The figures include the casualties from the March 11 quake and tsunami, as well as the several aftershocks that have since jolted northeast Japan.
Recent aftershocks have renewed concerns about the fragile condition of the Fukushima facility, which continues to leak radiation into the ocean and atmosphere. [via Stuff (NZ), The Telegraph (UK) NY Times]