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TOKYO, April 8 (UPI) -- A major aftershock in Japan did not further damage the Fukushima Daiichi reactors but did spill radioactive water at another plant, officials said Friday. Tokyo Electric Power Co. said workers had returned to Fukushima after the 7.1-magnitude aftershock that hit the ravaged northeast Thursday night, CNN reported. The initial reading, later corrected, was 7.4.
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The new earthquake was centered in Miyagi prefecture, already the worst hit by the horrific March 11 magnitude-9 earthquake and tsunami.
Radioactive water spilled from pools holding spent fuel rods at the Onagawa power plant in Miyagi, Japan's Nuclear and Industrial Safety Agency told Kyodo News.
Pools at Onagawa and the Higashidori nuclear station in Aomori prefecture, both operated by Tohoku Electric Power Co., lost their cooling functions for 20 to 80 minutes, but the temperature hardly rose, the agency said.
At Fukushima, workers struggling to avert a meltdown continued pumping nitrogen, an inert gas, into the No. 1 reactor Friday to prevent a hydrogen explosion, while at the same time battling high-level radioactive water flooding the basements of some of the reactors.
The nitrogen injections are intended to displace oxygen in the reactor shell, reducing the "extremely low" chance of another explosion, Tokyo Electric said.
Thursday's 11:32 p.m. shock, the latest in a continuing series of aftershocks that have tormented the region since March 11, also prompted the Japan Meteorological Agency to issue a tsunami warning that was canceled before 1 a.m. Friday. The shock was off Miyagi at a depth of about 25 miles.
Kyodo reported many emergency calls about injured people, fires and gas leakage in the affected region that also includes the Iwate, Akita, Yamagata and Fukushima prefectures. Millions of households in the region also experienced power outages, the government's nuclear safety agency said.
The Yomiuri Shimbun reported the aftershock killed two people and injured 132 in Miyagi prefecture.
Deputy Chief Cabinet Secretary Tetsuro Fukuyama said there were no notable changes in radiation levels near the Fukushima plant, but did not rule out more damage elsewhere from the aftershock.
Besides injecting nitrogen, Tokyo Electric also needs to control the radioactive water filling up the underground trenches to prevent them from overflowing.
The nitrogen injection into the No. 1 reactor, the first such, began Thursday and the utility said so far there has been no disruption. Similar injections are also planned for the Nos. 2 and 3 reactors.
The utility also planned to carry on with dumping low-level radioactive water from a nuclear waste disposal facility into the Pacific Ocean, a process described as unavoidable to create more storage room for the high-level contaminated water, which otherwise would overflow and interfere with other critical restoration work. About 8,000 tons of the low-level contaminated water remained to be dumped, expected by Saturday.
However, this process has raised serious concerns abroad about marine life contamination and the Japanese fishing industry, already hit by the March 11 disaster, has strongly protested the utility action and criticized the government.
A Tokyo Electric estimate says 25 percent of the nuclear fuel rods have been damaged at the No. 3 reactor. An earlier estimate said 70 percent of the No. 1 reactor's fuel rods and 30 percent of the No. 2 reactor's fuel rods had been damaged.
In Vienna, the U.N. International Atomic Energy Agency on its Web site said while the overall situation at the Fukushima plant "remains very serious," there are "early signs of recovery in some functions such as electrical power and instrumentation."
The Los Angeles Times reported U.S. officials said while the Fukushima plant is yet to be stabilized, evidence suggested a complete meltdown was unlikely since any overheating in past month has not resulted in any melting of the reactor vessels or their containment structures.
The Times report said based on that assessment, any large releases of radioactivity into the environment would be limited and the plant workers would be able to check additional damage to the reactors.
The United States planned to send two gigantic pumps, each weighing 190,000 pounds, CNN reported. The devices can pump both water and concrete.
The number of people confirmed killed by the national police agency in the March 11 disaster in the 12 prefectures is now nearly 12,600, while those listed as missing stood at more than 14,700. As of Thursday, about 160,000 people remained in about 2,300 shelters.
