Tokyo Electric Power Co. said fuel rods may be melting inside a nuclear reactor, heightening the danger of a meltdown as engineers struggle to stabilize the plant damaged by the biggest earthquake in Japan’s history.
The cooling system failed at the Daiichi No. 2 reactor yesterday, said Tokyo Electric, which runs the Fukushima nuclear plant 220 kilometers (135 miles) north of Tokyo. The fuel rods were exposed for a second time after water levels dropped, the company, known as Tepco, said early today.
Earlier a hydrogen explosion struck the No. 3 reactor, following a similar blast on March 12 at the No. 1 unit that destroyed the walls of its building. The utility has been flooding the three reactors with water and boric acid to reduce the potential for a large release of radiation following the March 11 earthquake-generated tsunami that smashed into the plant, disabling power supply and backup generators.
“It’s a situation that is requiring emergency measures to cool the reactors,” Andre-Claude Lacoste, chairman of French nuclear watchdog Autorite de Surete Nucleaire, said in Paris March 14. “If there is a complete meltdown of a core we will have a much more serious accident on our hands.”
An air flow gauge was accidentally turned off at the No. 2 reactor causing air pressure into the reactor to rise suddenly and blocking the flow of cooling water, Tokyo Electric said in a press conference posted on NHK television’s website early today. Tokyo Electric is now attempting to reopen the valve to release pressure building inside the reactor and inject water to cool the rods, the company said.
Japanese officials yesterday evacuated more than 200,000 people and handed out iodine, used to protect the thyroid from radioactivity, as they extended an exclusion zone around the plant to 20 kilometers.
Radiation levels reached 3,130 microsieverts an hour at the monitoring site near the gate of the plant as of 9:37 p.m. local time, twice the previous record, Tokyo Electric said. That level dropped to 326.2 microsieverts per hour at 10:35 p.m.
Prevailing winds in the area were heading east into the Pacific, which would carry radiation away, the Associated Press reported, citing Japan’s meteorological agency.
U.S Navy ships and planes involved in earthquake rescue efforts were moved after radiation was detected on three helicopters.
“Low level radioactivity” was detected on 17 air crew members when they returned to the USS Ronald Reagan aircraft carrier operating about 100 miles northeast from the plant, Navy spokesman Jeff Davis said in an e-mail.
The vessel containing the No. 3 reactor’s radioactive core is intact after yesterday’s blast, Chief Cabinet Secretary Yukio Edano told reporters. The likelihood of a large radiation leak is very small, even as radiation levels at the No. 3 reactor are rising, said Edano, the government’s spokesman.
At least four employees and two contractors were injured in the blast, Tokyo Electric said. The company’s shares slumped 24 percent.
There are six boiling-water reactors at the Fukushima Daiichi plant, three of which were shut for maintenance before the earthquake.
Unit No. 1 is a General Electric Co. model that can generate 439 megawatts of power and began commercial operation in 1971, according to the International Atomic Energy Agency. The No. 2 reactor was built by GE Toshiba and the No. 3 by Toshiba Corp.
Tokyo Electric said the sea water used to cool the reactors is being retained at the plant. “We will look into what we will do about the water,” spokesman Shogo Fukuda said by phone.
Flooding the reactors with sea water renders them useless for future power production. The practice is “horrible,” Lacoste of the French nuclear watchdog said. It’s never been the subject of experimentation because reactors normally require water that is as clean as possible so as not to clog up pipes and cooling circuits.
The disaster at Fukushima isn’t the first quake-related accident for Tokyo Electric.
A 6.8-magnitude temblor on July 16, 2007, caused a fire and radiation leaks that shut down the Kashiwazaki Kariwa nuclear plant, the world’s biggest. It took almost two years to restart.