ID :
173922
Thu, 04/07/2011 - 20:49
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https://oananews.org//node/173922
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Nitrogen, coolant water injection unaffected by Miyagi quake+
TOKYO, April 8 Kyodo -
An operation to reduce the risk of a hydrogen explosion at the crisis-hit Fukushima nuclear power plant by injecting nitrogen and pouring coolant water into reactors at the site was unaffected by a strong quake that hit northeastern Japan on Thursday night, the plant operator and the government's nuclear agency said.
A quake with a preliminary magnitude of 7.4 caused engineers engaged in recovery work at the Fukushima Daiichi station to temporarily evacuate, but no one was injured and no abnormalities have so far been detected in radiation levels near the plant, they said.
The workers are expected to inspect the site, which was ravaged by a magnitude 9.0 quake and tsunami on March 11, now that a tsunami warning issued for the area has been lifted.
Highly radioactive water that has been filling up underground trenches at the plant did not overflow, the government's Nuclear and Industrial Safety Agency said.
The mission to insert nitrogen into the plant's No. 1 reactor, which began in the early hours of Thursday, has gone smoothly, according to the plant's operator Tokyo Electric Power Co.
Pressure in the reactor's containment vessel has risen as expected, indicating the success of the operation. The operator known as TEPCO also plans to inject nitrogen into the Nos. 2 and 3 reactors for the same purpose, but the schedule has not been fixed.
TEPCO also continued on Thursday to dump water contaminated with low-level radiation into the Pacific Ocean to make room for the storage of highly radioactive water that has been hampering restoration work at the plant.
The utility said it will finish discharging 8,000 tons of contaminated water from a facility for nuclear waste disposal Friday. The operation to release 1,500 tons of groundwater contaminated with low-level radiation will be completed on Saturday, according to the government's nuclear safety agency.
The dumping of the tainted water has sparked concern over sea contamination among neighboring countries and strong protests from the domestic fishing industry.
In its operation to prevent a hydrogen explosion at the No. 1 reactor, TEPCO plans to inject nearly 6,000 cubic meters of nitrogen, an inert gas, into the reactor over six days.
The firm and the Nuclear and Industrial Safety Agency said they believe the chances are slim that another hydrogen explosion will occur immediately or that high volumes of radioactive substances will be emitted following the injection operation.
But TEPCO notified municipalities near the plant of the possibility of an increase in leaks of radioactive materials. Since the start of the operation, no major changes have been observed in radiation levels in the air, it said.
After the company successfully stopped leakage of highly radioactive water into the sea from a cracked pit Wednesday, it detected a 5-centimeter rise in the level of contaminated water in an underground trench connected to the No. 2 reactor building, from which the tainted water is believed to originate.
To prevent further contamination of the sea from radiation leaks, TEPCO will install iron sheets as well as ''silt fence'' barriers close to the No. 2 reactor water intake and other areas near the plant. The utility will also place 100 tons of sandbags at a breakwater, according to the agency.
Hidehiko Nishiyama, a spokesman for the nuclear regulatory body, said a worker who was making sandbags near the Nos. 5 and 6 reactor buildings was taken to a hospital Thursday afternoon after feeling ill, but it was confirmed that the worker had not been contaminated with radiation.
A seawater sample taken near the No. 2 reactor water intake on Saturday showed a radioactive iodine-131 concentration of about 7.5 million times the maximum level permitted under law, or about 300,000 becquerels per cubic centimeter.
But TEPCO said the concentration of iodine-131 was sharply lower at around 140,000 times the permitted level in a sample taken Wednesday after the leakage of highly radioactive water stopped.
Meanwhile, Chief Cabinet Secretary Yukio Edano said Thursday the government is considering allowing people who left areas within a 20-kilometer radius of the Fukushima plant to briefly return home and hinted at the possibility of issuing an evacuation order to people in the 20-30 km zone, who are currently advised to remain indoors.
Nishiyama said the nuclear agency will carefully examine conditions to allow the evacuees' temporary return with the Nuclear Safety Commission of Japan, a government panel, to ensure their safety.
According to estimates by TEPCO, nuclear fuel rods in the No. 1 reactor core are the most damaged compared with those in the Nos. 2 and 3 reactors. The cooling functions of all three units were lost after a magnitude 9.0 quake and tsunami ravaged the plant on March 11.
The company estimates that 70 percent of the fuel rods in the No. 1 reactor core have been damaged, compared with 30 percent in the No. 2 and 25 percent in the No. 3 reactor cores.
Hydrogen explosions occurred at the No. 1 and No. 3 reactors days after the twin disasters hit the site, blowing away the roofs and upper walls of the two units plus the No. 4 reactor's building.
Nishiyama said past explosions likely occurred due to hydrogen accumulation caused by the reaction of zirconium from melted fuel rods with steam from coolant water.
But there is now concern that hydrogen could accumulate in the No. 1 reactor under a different process involving radiation-induced decomposition of water into hydrogen and oxygen, he added.
The utility has been pouring massive amounts of water into the reactors and their spent nuclear fuel pools as a stopgap measure to cool them down. But the method is causing ''side effects,'' such as the detection of contaminated water in various parts of the nuclear complex and some leakage into the sea.
After releasing the low-level radioactive water from the plant to create room in a storage chamber, which can hold about half of the estimated 60,000 tons of contaminated water at the site, TEPCO will conduct repair work for about a week to ensure the facility can retain highly radioactive water without fear of outside leakage, Nishiyama said.
An operation to reduce the risk of a hydrogen explosion at the crisis-hit Fukushima nuclear power plant by injecting nitrogen and pouring coolant water into reactors at the site was unaffected by a strong quake that hit northeastern Japan on Thursday night, the plant operator and the government's nuclear agency said.
A quake with a preliminary magnitude of 7.4 caused engineers engaged in recovery work at the Fukushima Daiichi station to temporarily evacuate, but no one was injured and no abnormalities have so far been detected in radiation levels near the plant, they said.
The workers are expected to inspect the site, which was ravaged by a magnitude 9.0 quake and tsunami on March 11, now that a tsunami warning issued for the area has been lifted.
Highly radioactive water that has been filling up underground trenches at the plant did not overflow, the government's Nuclear and Industrial Safety Agency said.
The mission to insert nitrogen into the plant's No. 1 reactor, which began in the early hours of Thursday, has gone smoothly, according to the plant's operator Tokyo Electric Power Co.
Pressure in the reactor's containment vessel has risen as expected, indicating the success of the operation. The operator known as TEPCO also plans to inject nitrogen into the Nos. 2 and 3 reactors for the same purpose, but the schedule has not been fixed.
TEPCO also continued on Thursday to dump water contaminated with low-level radiation into the Pacific Ocean to make room for the storage of highly radioactive water that has been hampering restoration work at the plant.
The utility said it will finish discharging 8,000 tons of contaminated water from a facility for nuclear waste disposal Friday. The operation to release 1,500 tons of groundwater contaminated with low-level radiation will be completed on Saturday, according to the government's nuclear safety agency.
The dumping of the tainted water has sparked concern over sea contamination among neighboring countries and strong protests from the domestic fishing industry.
In its operation to prevent a hydrogen explosion at the No. 1 reactor, TEPCO plans to inject nearly 6,000 cubic meters of nitrogen, an inert gas, into the reactor over six days.
The firm and the Nuclear and Industrial Safety Agency said they believe the chances are slim that another hydrogen explosion will occur immediately or that high volumes of radioactive substances will be emitted following the injection operation.
But TEPCO notified municipalities near the plant of the possibility of an increase in leaks of radioactive materials. Since the start of the operation, no major changes have been observed in radiation levels in the air, it said.
After the company successfully stopped leakage of highly radioactive water into the sea from a cracked pit Wednesday, it detected a 5-centimeter rise in the level of contaminated water in an underground trench connected to the No. 2 reactor building, from which the tainted water is believed to originate.
To prevent further contamination of the sea from radiation leaks, TEPCO will install iron sheets as well as ''silt fence'' barriers close to the No. 2 reactor water intake and other areas near the plant. The utility will also place 100 tons of sandbags at a breakwater, according to the agency.
Hidehiko Nishiyama, a spokesman for the nuclear regulatory body, said a worker who was making sandbags near the Nos. 5 and 6 reactor buildings was taken to a hospital Thursday afternoon after feeling ill, but it was confirmed that the worker had not been contaminated with radiation.
A seawater sample taken near the No. 2 reactor water intake on Saturday showed a radioactive iodine-131 concentration of about 7.5 million times the maximum level permitted under law, or about 300,000 becquerels per cubic centimeter.
But TEPCO said the concentration of iodine-131 was sharply lower at around 140,000 times the permitted level in a sample taken Wednesday after the leakage of highly radioactive water stopped.
Meanwhile, Chief Cabinet Secretary Yukio Edano said Thursday the government is considering allowing people who left areas within a 20-kilometer radius of the Fukushima plant to briefly return home and hinted at the possibility of issuing an evacuation order to people in the 20-30 km zone, who are currently advised to remain indoors.
Nishiyama said the nuclear agency will carefully examine conditions to allow the evacuees' temporary return with the Nuclear Safety Commission of Japan, a government panel, to ensure their safety.
According to estimates by TEPCO, nuclear fuel rods in the No. 1 reactor core are the most damaged compared with those in the Nos. 2 and 3 reactors. The cooling functions of all three units were lost after a magnitude 9.0 quake and tsunami ravaged the plant on March 11.
The company estimates that 70 percent of the fuel rods in the No. 1 reactor core have been damaged, compared with 30 percent in the No. 2 and 25 percent in the No. 3 reactor cores.
Hydrogen explosions occurred at the No. 1 and No. 3 reactors days after the twin disasters hit the site, blowing away the roofs and upper walls of the two units plus the No. 4 reactor's building.
Nishiyama said past explosions likely occurred due to hydrogen accumulation caused by the reaction of zirconium from melted fuel rods with steam from coolant water.
But there is now concern that hydrogen could accumulate in the No. 1 reactor under a different process involving radiation-induced decomposition of water into hydrogen and oxygen, he added.
The utility has been pouring massive amounts of water into the reactors and their spent nuclear fuel pools as a stopgap measure to cool them down. But the method is causing ''side effects,'' such as the detection of contaminated water in various parts of the nuclear complex and some leakage into the sea.
After releasing the low-level radioactive water from the plant to create room in a storage chamber, which can hold about half of the estimated 60,000 tons of contaminated water at the site, TEPCO will conduct repair work for about a week to ensure the facility can retain highly radioactive water without fear of outside leakage, Nishiyama said.
