Agency doubles radioactive release estimate in early days of crisis
Jun. 7, 2011
The government's nuclear safety agency more than doubled its estimate Monday of the amount of radioactive materials emitted into the air during the early days of the nuclear crisis at the Fukushima Daiichi power plant, saying that the amount is believed to have totaled 770,000 terabecquerels.
The agency also issued its own assessment of the conditions of the Nos. 1 to 3 reactor cores based on the assumption that they suffered meltdowns, and pointed to the possibility that the process in the cases of the Nos. 1 and 2 reactors may have developed faster than estimated by plant operator Tokyo Electric Power Co.
The assessment by the Nuclear and Industrial Safety Agency is expected to be reflected in Japan's report on the accident to be submitted to a nuclear safety ministerial meeting hosted by the International Atomic Energy Agency later in the month.
In April, Japan raised the severity level of the ongoing crisis to the maximum 7 on an international scale -- equivalent to the 1986 Chernobyl disaster -- based on an estimate that radioactive materials far exceeding the criteria for level 7 have so far been released into the external environment.
The agency believed then that 370,000 terabecquerels of radioactive materials have been emitted into the air from the Nos. 1 to 3 reactors of the plant in northeastern Japan, but it revised the figure upward on Monday because it has found more radioactive leakage from the No. 2 reactor.
Level 7 accidents on the International Nuclear Event Scale correspond to the release into the external environment of radioactive materials equal to tens of thousands of terabecquerels of radioactive iodine 131. One terabecquerel equals 1 trillion becquerels.
As for the conditions of the reactor cores, the agency said the melted nuclear fuel of the No.1 reactor dropped to the bottom of the pressure vessel and damaged the vessel at about 8 p.m. on March 11, or about five hours after the devastating earthquake hit the plant. In the case of the No. 2 reactor, a similar event took place at about 10:50 p.m. on March 14, according to the agency.
Tokyo Electric, however, has said in its own analysis that it was in the morning of March 12 that the No. 1 reactor pressure vessel was damaged, and the early hours of March 16 that the No. 2 pressure vessel was damaged.
An agency official explained that the assessments of the agency and Tokyo Electric vary because of differences in assumptions over the amount of water injected into the reactor cores, which was conducted as an emergency measure to keep the fuel inside cool.
Meanwhile, the agency said it believes that the No. 3 reactor pressure vessel suffered damage at 10:10 p.m. on March 14, later than Tokyo Electric's estimate.
Hit by the magnitude 9.0 earthquake and 14-meter-high tsunami on March 11, the six-reactor nuclear complex lost nearly all of its power sources, leading the cooling functions of the reactors and spent nuclear fuel pools at the Nos. 1 to 4 units to fail.
(Distributed by Kyodo News on June 6, 2011)
The agency also issued its own assessment of the conditions of the Nos. 1 to 3 reactor cores based on the assumption that they suffered meltdowns, and pointed to the possibility that the process in the cases of the Nos. 1 and 2 reactors may have developed faster than estimated by plant operator Tokyo Electric Power Co.
The assessment by the Nuclear and Industrial Safety Agency is expected to be reflected in Japan's report on the accident to be submitted to a nuclear safety ministerial meeting hosted by the International Atomic Energy Agency later in the month.
In April, Japan raised the severity level of the ongoing crisis to the maximum 7 on an international scale -- equivalent to the 1986 Chernobyl disaster -- based on an estimate that radioactive materials far exceeding the criteria for level 7 have so far been released into the external environment.
The agency believed then that 370,000 terabecquerels of radioactive materials have been emitted into the air from the Nos. 1 to 3 reactors of the plant in northeastern Japan, but it revised the figure upward on Monday because it has found more radioactive leakage from the No. 2 reactor.
Level 7 accidents on the International Nuclear Event Scale correspond to the release into the external environment of radioactive materials equal to tens of thousands of terabecquerels of radioactive iodine 131. One terabecquerel equals 1 trillion becquerels.
As for the conditions of the reactor cores, the agency said the melted nuclear fuel of the No.1 reactor dropped to the bottom of the pressure vessel and damaged the vessel at about 8 p.m. on March 11, or about five hours after the devastating earthquake hit the plant. In the case of the No. 2 reactor, a similar event took place at about 10:50 p.m. on March 14, according to the agency.
Tokyo Electric, however, has said in its own analysis that it was in the morning of March 12 that the No. 1 reactor pressure vessel was damaged, and the early hours of March 16 that the No. 2 pressure vessel was damaged.
An agency official explained that the assessments of the agency and Tokyo Electric vary because of differences in assumptions over the amount of water injected into the reactor cores, which was conducted as an emergency measure to keep the fuel inside cool.
Meanwhile, the agency said it believes that the No. 3 reactor pressure vessel suffered damage at 10:10 p.m. on March 14, later than Tokyo Electric's estimate.
Hit by the magnitude 9.0 earthquake and 14-meter-high tsunami on March 11, the six-reactor nuclear complex lost nearly all of its power sources, leading the cooling functions of the reactors and spent nuclear fuel pools at the Nos. 1 to 4 units to fail.
(Distributed by Kyodo News on June 6, 2011)
