Japanese officials were trying frantically to thwart partial meltdowns presumed under way Sunday at two earthquake-stricken nuclear reactors in Japan.
Fuel rods were briefly exposed and radiation levels briefly rose above the legal limit at the second reactor Sunday, said Chief Cabinet Secretary Yukio Edano.
A partial meltdown in the unit is “highly possible,” he told reporters. “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 also said a hydrogen explosion could occur at the reactor, Unit 3 of the Fukushima Daiichi nuclear complex. That would follow a Saturday blast at Unit 1 of the same complex as operators attempted to prevent a nuclear meltdown by injecting sea water into it.
Japan’s largest electric utility Sunday released what it said was slightly radioactive air at Unit 3.
Both reactors are among three shut down Friday at the Fukushima Daiishi plant when their cooling functions stopped after the area was jolted by a magnitude 8.9 earthquake.
Tokyo Electric Co., or TEPCO, Saturday began pouring seawater and boric acid into its Fukushima Daiichi power plant Unit 1 reactor, whose core partially melted. On Sunday TEPCO released air containing radioactive materials for more than 2 hours and injected water at the Unit 3 nuclear reactor container vessel to reduce pressure and temperature to save the reactor from a possible meltdown.
Critical core cooling systems failed at both reactors. The Unit 2 reactor, though shut down by the quake, was not in the same trouble.
Released steam raised radiation levels above safety limits outside the Unit 3 reactor Sunday, TEPCO officials said, adding they informed the government of an “emergency situation.” Still, they said, there was no immediate threat to human health.
Edano said the radiation levels later fell.
Tepco / Reuters
A similar radiation increase was seen Saturday during venting at the No. 1 reactor before it exploded. The blast destroyed the exterior walls of a building, but did not breach the steel housing enveloping the reactor there, officials said.
Radioactive cesium and iodine were detected near the facility Saturday, indicating that the melting had occurred, Kyodo News Service reported.
Officials said that at one point, the Unit 1 was releasing each hour the amount of radiation a person normally absorbs from the environment each year.
It is the first time a Japanese nuclear plant has ever experienced any level of reactor core melting.
TEPCO on Sunday also said it was preparing pressure reducing measures for its nearby Fukushima Daini Nuclear Power Station, where four reactors were shut down due to earthquakes. Releases of air with radioactive material were being considered for Daini units 1, 2, and 3.
Earlier Edano said TEPCO has begun new cooling operations to fill the Daiishi No. 1 reactor where the melting occurred with seawater and pour in boric acid, which absorbs neutrons, an operation expected to take several hours, Kyodo reported.
Filling the entire reactor container with seawater will take about 10 days, Edano said. It is likely that the reactor will have to be decommissioned because of the contamination by salts and other substances, experts said, according to Kyodo.
Edano on Sunday said the cooling operation at Unit 1 was going smoothly.
Robert Alvarez, senior scholar at the Institute for Policy Studies and former senior policy adviser to the U.S. secretary of energy, said in a briefing for reporters that the seawater was a desperate measure.
“It’s a Hail Mary pass,” he said.
He said that the success of using seawater and boron to cool the reactor will depend on the volume and rate of their distribution.
The evacuation zone around the facilities was doubled in size from 6 miles to 12 miles. More than 210,000 people had been evacuated from the area by early Sunday morning, and evacuations were continuing, the safety agency said.
Footage on Japanese TV showed the explosion had crumbled the building’s walls, leaving only a skeletal metal frame standing. Its roof had also been blown off. Plumes of smoke spewed out of the plant, 20 miles from Iwaki.
The Japanese authorities have classified the event at Fukushima Daiichi Unit 1 as a level 4 “accident with local consequences” on the International Nuclear and Radiological Event Scale (INES). The scale is used to consistently communicate the safety significance of events associated with sources of radiation. The scale runs from 0 (deviation — no safety significance) to 7 (major accident).