Editor's note: Find out more about Japan's nuclear reactors in this expert Q and A from CNN's Wayne Drash.
Tokyo (CNN) -- A new explosion rocked the earthquake-damaged Fukushima Daiichi nuclear power plant in northeastern Japan early Tuesday from a reactor that workers had struggled to keep under control since a blast at a neighboring unit, the plant's owner announced.
The "explosive impact" took place shortly after 6 a.m. Tuesday (5 p.m. Monday ET) inside the housing of the plant's No. 2 reactor, officials of the Tokyo Electric Power Company reported at a news conference. No further details were immediately released, but TEPCO said all but about 50 workers were evacuated following the blast due to elevated radiation levels.
"We are continuing the water injection into the pressure vessels, but the operators who are not directly engaged in this operation are being evacuated to safer locations," a TEPCO executive told reporters at a news conference Tuesday morning.
Pressure readings indicated some damage to the No. 2 reactor's suppression pool, a donut-shaped reservoir at the base of the reactor containment vessel. Workers have been trying to keep sea water pouring into the No. 2 reactor since Monday, when a hydrogen explosion at reactor No. 3 damaged the cooling system at unit 2 and injured 11 people, Japanese authorities said.
A similar hydrogen explosion on Saturday blew the roof off the containment structure around the No. 1 reactor.
Japan's Nuclear and Industrial Safety Agency said Tuesday that up to 2.7 meters (8.8 feet) of the No. 2 reactor's control rods -- about half -- have been uncovered. Radiation levels at the plant have spiked to as much as 3,130 micosieverts per hour -- more than a typical year's dose from natural sources, but about the same level as a patient receiving a CT scan would get in a matter of minutes, according to David J. Brenner, director of the Center for Radiological Research at Columbia University in New York.
Yukio Edano, Japan's chief Cabinet secretary, said he could not rule out the possibility of a meltdown at all three troubled reactors at the plant. While sea water was being pumped into the reactors in an effort to prevent further damage, "It cannot necessarily be called a stable situation," Edano said early Tuesday.
The buildup of hydrogen in the reactor vessels is "the first sign that things are going haywire," said Kenneth Bergeron, a physicist who used to work at the Energy Department's Sandia National Laboratories in New Mexico. The release of radioactive material such as cesium, a reactor byproduct that has been detected outside the Fukushima Daiichi plant, is another, he said.
"What is fairly clear, from the release of hydrogen and the fission products, is that all of these reactors have probably had fuel rods exposed for significant periods of time over a portion of their length," Bergeron told CNN.
Authorities began pumping a mix of sea water and boron into the No. 2 reactor after Monday's explosion, as they have been doing with units 1 and 3. But the pump ran low on fuel when workers left it unattended, and the water soon burned off and exposed the reactor's fuel rods, allowing them to emit levels of heat and steam that can melt the reactor's core.
When that problem was resolved, Edano said, a new problem sent the water levels plummeting again. A valve that was supposed to be open to allow the heat and steam to escape was closed, causing pressure to build up inside the reactor building, according to TEPCO. But pumping had resumed by early Tuesday, Edano said.
Officials earlier said that they were operating on the presumption that there may be a partial meltdown in the No. 3 and No. 1 nuclear reactors at the Daiichi plant. Authorities have not yet been able to confirm a meltdown, because it is too hot inside the affected reactors to check.
If the effort to cool the nuclear fuel inside the reactor fails completely -- a scenario that experts who have spoken to CNN say is unlikely -- the resulting release of radiation could cause enormous damage to the plant, and possibly release radiation into the atmosphere or water. That could lead to widespread cancer and other health problems, experts say.
But Bergeron said that while it is likely the reactor cores have been damaged, "it will have to get a lot hotter" for the dense uranium in the reactor's fuel rods to melt down. That would give authorities and the surrounding population time to prepare.
"I believe they would be able to tell from various signals having to do with release of radioactivity and other things that things were a lost cause, you might say, and they might start initiating additional evacuations," Bergeron said.
"There would be warning, but we're talking massive, massive responses required," he added.
About 200,000 people have evacuated the area following a government order over the weekend. And after Monday's blast, authorities ordered at least 500 residents remaining within 20 kilometers (12 miles) of the plant to stay inside, Edano said.
And low levels of radiation were detected at least as far as 100 miles (about 160 kilometers) northeast of the plant, according to the U.S. Navy, which repositioned ships and planes after detecting low-level "airborne radioactivity." Tests also detected low levels of radioactivity on 17 U.S. Navy helicopter crew members when they returned to the aircraft carrier USS Ronald Reagan, but no further contamination was detected after the crew members washed with soap and water, the Navy said.
The Navy said the maximum potential radiation dose received by any ship personnel when it passed through the area was "less than the radiation exposure received from about one month of exposure to natural background radiation from sources such as rocks, soil, and the sun."
The United States has sent a team of experts to assist Japan at the nuclear site, including two cooling experts. U.S. officials are also "assembling a team of experts that would be dispatched in the near future," Greg Jaczko, chairman of the U.S. Nuclear Regulatory Commission, said Monday.
Japan has asked for additional types of equipment that will help provide water and keep the reactors cool, he said.
Based on the reactor design and nature of the accident, there is very low probability of any harmful radiation levels reaching the United Sates, including Hawaii and U.S. territories, Jaczko said.
http://edition.cnn.com/2011/WORLD/asiapcf/03/14/japan.nuclear.reactors/index.html?hpt=T1
Tokyo (CNN) -- A new explosion rocked the earthquake-damaged Fukushima Daiichi nuclear power plant in northeastern Japan early Tuesday from a reactor that workers had struggled to keep under control since a blast at a neighboring unit, the plant's owner announced.
The "explosive impact" took place shortly after 6 a.m. Tuesday (5 p.m. Monday ET) inside the housing of the plant's No. 2 reactor, officials of the Tokyo Electric Power Company reported at a news conference. No further details were immediately released, but TEPCO said all but about 50 workers were evacuated following the blast due to elevated radiation levels.
"We are continuing the water injection into the pressure vessels, but the operators who are not directly engaged in this operation are being evacuated to safer locations," a TEPCO executive told reporters at a news conference Tuesday morning.
Pressure readings indicated some damage to the No. 2 reactor's suppression pool, a donut-shaped reservoir at the base of the reactor containment vessel. Workers have been trying to keep sea water pouring into the No. 2 reactor since Monday, when a hydrogen explosion at reactor No. 3 damaged the cooling system at unit 2 and injured 11 people, Japanese authorities said.
A similar hydrogen explosion on Saturday blew the roof off the containment structure around the No. 1 reactor.
Japan's Nuclear and Industrial Safety Agency said Tuesday that up to 2.7 meters (8.8 feet) of the No. 2 reactor's control rods -- about half -- have been uncovered. Radiation levels at the plant have spiked to as much as 3,130 micosieverts per hour -- more than a typical year's dose from natural sources, but about the same level as a patient receiving a CT scan would get in a matter of minutes, according to David J. Brenner, director of the Center for Radiological Research at Columbia University in New York.
Yukio Edano, Japan's chief Cabinet secretary, said he could not rule out the possibility of a meltdown at all three troubled reactors at the plant. While sea water was being pumped into the reactors in an effort to prevent further damage, "It cannot necessarily be called a stable situation," Edano said early Tuesday.
The buildup of hydrogen in the reactor vessels is "the first sign that things are going haywire," said Kenneth Bergeron, a physicist who used to work at the Energy Department's Sandia National Laboratories in New Mexico. The release of radioactive material such as cesium, a reactor byproduct that has been detected outside the Fukushima Daiichi plant, is another, he said.
"What is fairly clear, from the release of hydrogen and the fission products, is that all of these reactors have probably had fuel rods exposed for significant periods of time over a portion of their length," Bergeron told CNN.
Authorities began pumping a mix of sea water and boron into the No. 2 reactor after Monday's explosion, as they have been doing with units 1 and 3. But the pump ran low on fuel when workers left it unattended, and the water soon burned off and exposed the reactor's fuel rods, allowing them to emit levels of heat and steam that can melt the reactor's core.
When that problem was resolved, Edano said, a new problem sent the water levels plummeting again. A valve that was supposed to be open to allow the heat and steam to escape was closed, causing pressure to build up inside the reactor building, according to TEPCO. But pumping had resumed by early Tuesday, Edano said.
Officials earlier said that they were operating on the presumption that there may be a partial meltdown in the No. 3 and No. 1 nuclear reactors at the Daiichi plant. Authorities have not yet been able to confirm a meltdown, because it is too hot inside the affected reactors to check.
If the effort to cool the nuclear fuel inside the reactor fails completely -- a scenario that experts who have spoken to CNN say is unlikely -- the resulting release of radiation could cause enormous damage to the plant, and possibly release radiation into the atmosphere or water. That could lead to widespread cancer and other health problems, experts say.
But Bergeron said that while it is likely the reactor cores have been damaged, "it will have to get a lot hotter" for the dense uranium in the reactor's fuel rods to melt down. That would give authorities and the surrounding population time to prepare.
"I believe they would be able to tell from various signals having to do with release of radioactivity and other things that things were a lost cause, you might say, and they might start initiating additional evacuations," Bergeron said.
"There would be warning, but we're talking massive, massive responses required," he added.
About 200,000 people have evacuated the area following a government order over the weekend. And after Monday's blast, authorities ordered at least 500 residents remaining within 20 kilometers (12 miles) of the plant to stay inside, Edano said.
And low levels of radiation were detected at least as far as 100 miles (about 160 kilometers) northeast of the plant, according to the U.S. Navy, which repositioned ships and planes after detecting low-level "airborne radioactivity." Tests also detected low levels of radioactivity on 17 U.S. Navy helicopter crew members when they returned to the aircraft carrier USS Ronald Reagan, but no further contamination was detected after the crew members washed with soap and water, the Navy said.
The Navy said the maximum potential radiation dose received by any ship personnel when it passed through the area was "less than the radiation exposure received from about one month of exposure to natural background radiation from sources such as rocks, soil, and the sun."
The United States has sent a team of experts to assist Japan at the nuclear site, including two cooling experts. U.S. officials are also "assembling a team of experts that would be dispatched in the near future," Greg Jaczko, chairman of the U.S. Nuclear Regulatory Commission, said Monday.
Japan has asked for additional types of equipment that will help provide water and keep the reactors cool, he said.
Based on the reactor design and nature of the accident, there is very low probability of any harmful radiation levels reaching the United Sates, including Hawaii and U.S. territories, Jaczko said.
http://edition.cnn.com/2011/WORLD/asiapcf/03/14/japan.nuclear.reactors/index.html?hpt=T1
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