Japanese authorities said Sunday that efforts to restart the cooling system at one of the nuclear reactors damaged by Friday’s earthquake had failed, even as officials struggled to bring several other damaged reactors under control.
In an effort to relieve pressure at the failing reactor, Fukushima Daiichi’s unit 3, the utility said it released “air containing radioactive materials.” Chief Cabinet Secretary Yukio Edano said radiation at the reactor exceeded legal limits and that it was “highly possible” a partial meltdown was under way.
“Because it’s inside the reactor, we cannot directly check it, but we are taking measures on the assumption of the possible partial meltdown,” he told reporters, according to the Associated Press.
Hours before Edano’s remarks, authorities began evacuating more than 200,000 residents from a 12.5-mile radius around two nuclear power complexes, made preparations to distribute potassium iodide pills, and warned people in the vicinity to stay inside and cover their mouths if they ventured outdoors.
Tokyo Electric Power Co., owner of the two heavily damaged complexes, took the unprecedented step of pumping seawater mixed with boric acid into the core of another reactor, Fukushima Daiichi’s unit 1 reactor, to tame ultra-high temperatures from fuel rods that had been partially exposed. In keeping with the natural as well as mechanical challenges of the week, the company had to delay the plan briefly after another, more mild, earthquake rocked the area and led to another tsunami warning.
The battle at that reactor was just one of several being waged in the worst nuclear power crisis in a quarter-century.
Tokyo Electric said it had also vented or planned to vent steam and gas containing small amounts of radioactivity from six of its other reactor units. The company said that one employee, who had been working inside a reactor building, had been hospitalized for radiation exposure.
Federal safety agency officials said that as many as 160 people had been exposed to radiation from the plants. “Only the gravest danger would justify an evacuation at such a moment,” said Peter Bradford, a former commissioner at the U.S. Nuclear Regulatory Commission.
The evacuation, wider than announced the day before, followed an explosion Saturday that destroyed a building that housed both the reactor vessel and its containment structure. Four workers were injured, but Japanese authorities said the containment building was intact.
The explosion was yet another indicator of dire problems inside Fukushima Daiichi Unit 1, problems that might be plaguing other units as well. The explosion was caused by hydrogen, which nuclear experts said could only have been produced from inside the reactor vessel by the exposure of zirconium cladding that surrounds the fuel rods. Those rods are supposed to be covered by water, but at very high temperatures, steam reacts with the zirconium and produces hydrogen.
When pressure rose in the reactor vessel, it vented the gas into the containment structure and then into the outer building. Experts believe devices designed to ignite the hydrogen before it reached dangerous levels were not working because of power failures.
Those power failures helped start the crisis at the nuclear plants. After grid power was knocked out by the quake, the tsunami flooded and disabled backup diesel generators, and battery power ran out. Margaret Harding, a U.S. nuclear safety consultant in touch with experts in Japan, said that the entire complex was blacked out for a period of time before new backup generators arrived.
Another indication that the fuel rods in Fukushima Daiichi Unit 1 were exposed is that Japan’s Nuclear and Industrial Safety Agency (NISA) said Saturday that the reactor could be nearing a meltdown and that two radioactive substances, cesium and radioactive iodine, had already been detected nearby.
The explosion also rattled public confidence, sparking a run on bottled water in Tokyo.
Japan has an ambivalent relationship with nuclear issues. As victim of the only wartime nuclear bombings, it opposes such weapons. But as a resource-scarce country, it has turned to nuclear power to help fuel its economy.
Japan’s dependence on nuclear energy soared after 1973 in response to skyrocketing oil prices that year. In 2002, the country mapped a future that sought to decrease the country’s greenhouse gas emissions by further increasing its reliance on nuclear power. Current plans call for 50 percent of the country’s electricity to come from nuclear plants by 2017, up from about 30 percent today. The country has 54 nuclear reactors.
Fukushima Daiichi Unit 1 is one of the oldest operating nuclear plants in Japan, turning 40 years old on March 26. NISA, the country’s regulatory authority for the sector, licenses reactors to operate for 40 years – meaning that Unit 1 was scheduled to be taken offline this month. It is unclear whether NISA had planned to extend the reactor’s license.
There are 23 reactors in the United States with the same design as Fukushima Daiichi Unit 1.
Experts said that the decision to pump seawater into the unit was a recognition that the elaborate system of valves, pumps and pipes, and the layers of steel and concrete, might not be enough to guarantee that the nuclear facility could avoid a disaster of Chernobyl proportions.
The water and boric acid would absorb neutrons, Tokyo Electric said. But experts said it would also make it unlikely that the plant would operate again.
“We’re past worrying about ruining the reactor,” said Victor Gilinsky, another former commissioner at the U.S. Nuclear Regulatory Commission. “It’s gone.”
Nuclear safety experts were seeking answers to other questions about Japan’s nuclear facilities that have been obscured by the focus on the Fukushima reactors. The nuclear plants also have spent fuel pools that some experts say may have spilled during the earthquake and its aftershocks. Tokyo Electric has not commented yet on those pools, which in the case of the GE-designed reactors are located on the roof, possibly making them vulnerable.
Similar pools are found at other nuclear power plants around the country.
The U.S. government and private companies said they had offered assistance to Japan but had not received any requests. The Energy Department said it was “in close contact” with its Japanese counterparts and would “provide whatever assistance they request to help them bring the reactors under control.”
