Kyodo News, Tokyo, Mar 14, 2011
Japanese authorities scrambled Sunday to avert a nuclear disaster, injecting seawater into overheating reactors and relieving the pressure inside a nuclear power plant in Fukushima Prefecture that was hit and shut down as a result of Friday's devastating earthquake.
While acknowledging that fuel rods of the No. 3 reactor at the Fukushima No. 1 [Daiichi] plant [150 miles---240km---north of Tokyo] may have been deformed due to excessive heat, Chief Cabinet Secretary Yukio Edano denied it has led to a ''meltdown,'' a critical situation where fuel rods have melted and been destroyed.
Hidehiko Nishiyama, a senior official of the Economy, Trade and Industry Ministry indicated, however, that the reactor core has melted partially, telling a news conference, ''I don't think the fuel rods themselves have been spared damage.''
Cooling failure led the fuel rods at another reactor at the same plant to partially melt Saturday, and an ensuing explosion that blew away part of a building housing the reactor triggered fears of a nuclear disaster.
Edano, the top government spokesman, warned that a hydrogen explosion similar to one that hit the No. 1 reactor could occur at the No. 3 reactor.
Large amounts of hydrogen were formed when the water injection procedure temporarily ran into trouble and hydrogen may have filled the upper part of a building housing the No. 3 reactor, Edano said at a separate news conference.
The developments came after the cooling systems for some of the plant's reactors failed following the magnitude 9.0 earthquake and tsunami caused by it hit northeastern and eastern Japan on Friday.
The plant operator, Tokyo Electric Power Co., commonly known as TEPCO, began injecting fresh water into the No. 3 reactor on Sunday after coolant water levels fell, while letting out radioactive steam to relieve pressure that had built up inside.
But after trouble developed with a fresh water pump, the company was forced to pour seawater into it to avoid a meltdown, a step that will eventually lead to the reactor's dismantlement. As a result, water levels rose but the water-level gauge has stopped indicating a rise, Edano said.
An official of the government's Nuclear and Industrial Safety Agency said half of the roughly 4-meter rods were still exposed late Sunday, but that seawater kept being pumped into the reactor vessel.
The procedure temporarily exposed the top parts of MOX fuel rods above coolant water by nearly 3 meters. MOX fuel refers to plutonium-uranium mixed oxide fuel, used for so-called ''pluthermal'' power generation.
Radiation around the reactor rose three times the benchmark limit to 1,557 micro sievert per hour at 1:52 p.m. Sunday, but the figure went down to 184 about 50 minutes later. Given the radiation level, Edano said a hydrogen explosion is unlikely to affect human health even if one occurred.
Meanwhile, radiation monitored at the Onagawa nuclear power plant in Miyagi Prefecture on the Pacific coast shot up from late Saturday through early Sunday, Tohoku Electric Power Co. said, adding that radiation levels were low but about 700 times as high as normal.
The government agency said it was likely caused by radioactive substances that scattered when a hydrogen explosion hit the troubled Fukushima plant, about 120 kilometers south.
The No. 3 reactor was the sixth reactor overall at the Fukushima No. 1 and No. 2 plants, which are located about 11 km apart, to experience cooling failure since the massive earthquake and ensuing tsunami struck the power facilities.
The nuclear crisis has raised fears of radiation exposure.
Nineteen people who had evacuated from an area within 3 km of the No. 1 plant were found exposed to radiation, joining three others already confirmed to have been exposed, the Fukushima prefectural government said Sunday.
In addition, about 160 people are feared to have been exposed to radiation, according to the government agency.
The Fire and Disaster Management Agency said 15 people were found to have been contaminated with radioactive material at a hospital located within 10 km of the reactor.
To measure radiation for residents who may have been exposed to it and determine whether they need emergency treatment, the National Institute of Radiological Sciences sent 17 doctors and experts to the city of Fukushima on Sunday.
Edano, the chief Cabinet secretary, said there is little likelihood that radiation to which some residents have been exposed was serious enough to cause health damage.
Meanwhile, electric power companies in other regions and Japan Nuclear Fuel Ltd. have dispatched a total of 48 people to help TEPCO deal with the crisis at the two nuclear power plants in Fukushima.
Late Sunday, Masataka Shimizu, president of TEPCO, apologized for causing the leaks of radioactive substances, while blaming tsunami beyond their projections for the reactor failures.
''The tsunami was greater than we had projected,'' he said at a news conference. ''The largest factor was that we lost function due to equipment failure (caused by the tsunami).''
An explosion Saturday at the No. 1 plant blew away the roof and part of the walls of the building housing its No. 1 reactor's container.
The government and nuclear authorities said there was no damage to a steel container housing the reactor, noting that the blast occurred as vapor from the container turned into hydrogen and mixed with oxygen outside.
On Sunday, TEPCO continued new cooling operations to fill the troubled No. 1 reactor with seawater and pour in boric acid to prevent an occurrence of criticality.
The country's first partial melting of a reactor core was confirmed Saturday through the detection near the facility of radioactive cesium and iodine -- materials created following atomic fission.
Coolant water had been being pumped into the No. 3 reactor through supply equipment since the reactor shut down automatically following the quake, but the supply stopped on Sunday morning, making it necessary to pump seawater into the facility.
Following the explosion, the authorities expanded from 10 km to 20 km [12 miles] the radius of the evacuation area for residents living in the vicinity of the Fukushima plants. [Full story]
(Japan's nuclear safety agency rated the No. 1 reactor explosion at four on the international scale of zero to seven. The 1979 Three Mile Island accident in the United States was rated five, while the 1986 Chernobyl disaster was a seven. Russia is boosting LNG supplies to Japan, which is facing electric power shortages after Friday's massive earthquake shut nuclear reactors located in the worst affected areas. TEPCO said Monday it will start an unprecedented rationing of power at 10 a.m. or later rather than 6:20 a.m. as initially planned in the wake of Friday's powerful earthquake that hit Japan and crippled some nuclear power plants. Japan gets about 30% of its electricity from nuclear power. A hydrogen explosion occurred Monday morning at the quake-hit Fukushima No. 1 nuclear power plant's troubled No. 3 reactor, injuring three workers, but the reactor's container was not damaged, the government's nuclear safety agency and the plant's operator said. ''We judge that the possibility of a large amount of radioactive materials flying off from there is low,'' Chief Cabinet Secretary Yukio Edano told a news conference, adding that the injection of seawater to cool down the No. 3 reactor is continuing. -- D.R.)