TOKYO — More than 450,000 households remained without electricity on Friday evening after the strongest aftershock to hit since the March 11 earthquake and tsunami in Japan rocked a wide section of the country’s northeast.
Of about 3.6 million households initially affected, more than 450,000 were still without power Friday evening, The Associated Press reported, citing the utility that serves the region.
Early Friday, injuries were reported in Sendai City and across the region, and blackouts continued in some areas, according to NHK. Five coal-powered power plants also shut down, adding to concerns over energy shortages.
The aftershock on Thursday night prompted a tsunami alert, raised fears of new strains on the crippled Fukushima Daiichi nuclear plant and knocked out external power at three other nuclear facilities.
The Tokyo Electric Power Company, which runs the Fukushima plant, said Friday that it had found no new damage to the plant, and workers had resumed work to identify the source of leaks, found last week, of radioactive water into pipes and tunnels under the complex. Monitoring posts at the plant were not showing any immediate increase in radiation levels, the company said.
The company also said that the dumping of “relatively low radiation water” into the Pacific Ocean was expected to be completed on Saturday, Reuters reported. The dumping is intended to make room in storage containers for much more highly radioactive water that has flooded some buildings at the plant.
No tsunami was detected, the Japan Meteorological Agency said. The aftershock had a magnitude of 7.1, according to the United States Geological Survey; last month’s quake, which devastated much of the northeastern coast, was measured at 9.0.
But the agency warned of more aftershocks going forward. Many coastal communities were ravaged last month, and some have become even more vulnerable to tsunami waves because sea walls were breached and land levels sank.
A big aftershock is thought to pose an additional risk to the Fukushima plant because its containment structures, now filled with water that is highly radioactive, may be more vulnerable to rupture, according to an assessment by the United States Nuclear Regulatory Commission in late March.
The temblor also underscored the sensitivity of other power plants in the region to seismic shocks.
Two other nuclear facilities — a fuel reprocessing plant at Rokkasho and a power plant at Higashidori, both in northern Aomori Prefecture — ran temporarily on emergency diesel generators after their external power was knocked out. Grid power was restored at both plants on Friday morning, according to Japan’s nuclear regulator, the Nuclear and Industrial Safety Agency.
The single reactor at Higashidori is shut down for maintenance, and all nuclear fuel had been transferred to the facility’s spent-fuel pools, which are being cooled by back-up diesel power, according to the operator, Tohoku Electric.
A third site, the Onagawa Nuclear Power Station in Miyagi Prefecture, lost two of its three external power systems, and cooling stopped temporarily at a spent-fuel pool there, Tohoku Electric said. All three plants have been shut down since the March 11 quake, but power is needed to cool the nuclear fuel.
The Associated Press reported that at the Onagawa plant some radioactive water had splashed out of pools but did not leave containment buildings, according to Tohoku Electric. Such splash-out is "not unusual, although it is preferable that it doesn’t happen," according to Tomoho Yamada, an official with the nuclear agency.
A spokesman for agency, Hidehiko Nishiyama, said that "closer inspection could find more problems" but that no radiation was released into the environment, The A.P. reported.
The aftershock hit at 11:32 p.m. local time on Thursday and was centered 41 miles east of Sendai, 72 miles from Fukushima and 205 miles from Tokyo, officials said. It was about 30 miles below the ocean floor, about 10 miles deeper than the March 11 quake. Hundreds of aftershocks have followed the initial quake, but Thursday’s was the strongest, according to the United States Geological Survey.
The police say about 12,800 people have died as a result of the March 11 earthquake and tsunami. More than 14,900 are listed as missing.