Aftershocks rattling Japan after the nation’s record quake on March 11 may continue for at least six months, increasing the risk of damage to a crippled nuclear plant at the center of the worst nuclear crisis since Chernobyl.
“Aftershocks as big as magnitude-7 are likely to continue hitting in eastern and northern Japan for at least six months,” said Teruyuki Kato, a professor at the University of Tokyo’s Earthquake Research Institute.
The magnitude-9 earthquake and tsunami last month left more than 28,000 people dead or missing and knocked out back-up power and cooling systems at the Fukushima Dai-Ichi nuclear plant north of Tokyo, causing explosions and radiation leaks. Hundreds of aftershocks, including three stronger than magnitude-7, have struck the region, causing more deaths and hindering work to cool damaged reactors.
Reactor containment vessels at the nuclear plant that have been flooded with tons of water to keep fuel rods cool are at risk in the event of another big quake, said Kazuya Idemitsu, a professor of nuclear engineering at Kyushu University.
“One of my concerns is that the containment chambers may have been compromised to some extent,” he said. Another strong aftershock might damage parts such as “pipe joints and cause more radioactive water to leak.”
Still, the pressure vessels inside the containment chambers that surround the cores shouldn’t be at risk, said Idemitsu. “The pressure vessels can withstand another magnitude-8 earthquake,” he said.
Tepco spokesman Takeo Iwamoto said the company hasn’t found damage to the site after the aftershocks. A magnitude-6.1 quake struck off Japan at 5:57 a.m. today, according to the U.S. Geological Survey.
“The worst-case scenario is for a 10-meter tsunami to swamp the Pacific Ocean coast in northeastern Japan if a magnitude-8 aftershock strikes offshore,” Kato said.
Tepco is still using emergency pumps to cool the reactors and pools holding spent fuel, more than one month after the initial rupture. Three blasts damaged reactor buildings and spewed radiation into the air last month.
“The integrity of the core facilities at Fukushima Dai-Ichi will probably be maintained because they are designed to withstand earthquakes,” said Tomoko Murakami, a nuclear researcher at the Institute of Energy Economics, Japan. “The big problem is the radioactive water that is hampering efforts to bring the cooling system on line.”
The earthquake and tsunami and the resulting nuclear disaster show that atomic energy should be phased out in Japan, according to a group that opposes such power stations.
“There is no such thing as a safe nuclear power plant in Japan,” because it’s an earthquake-prone country, said Philip White, international liaison officer at the Citizens’ Nuclear Information Center in Tokyo.