The government's nuclear watchdog on Tuesday raised its assessment of the severity of the nuclear crisis at the Fukushima No. 1 power plant to the highest level under the international standard, putting it on a par with the 1986 Chernobyl catastrophe - the worst atomic power disaster in history.
Photo: Kim Kyung-Hoon/Reuters
Four-year-old Saki Watanabe is tested for possible nuclear radiation at an evacuation centre in Koriyama, Fukushima Prefecture, northern Japan, on Friday, located about 70 kilometres from the tusnami-crippled nuclear reactor.
The latest assessment, which raises the level from 5 to 7, highlights Tokyo's failure so far to defuse the nuclear crisis at the crippled Fukushima plant more than a month after the March 11 earthquake and tsunami, and forces the government to acknowledge it as one of the two worst nuclear disasters ever.
Still, Nuclear and Industrial Safety Agency spokesman Hidehiko Nishiyama attempted to play down the impact of the assessment, saying the severity of the Fukushima crisis is nowhere near that of Chernobyl, where huge amounts of radioactive materials were spewed into the environment.
"It's considerably different from Chernobyl," said Nishiyama. "The amount of radioactive materials released at Fukushima is about a tenth of that (of) Chernobyl."
The International Atomic Energy Agency's International Nuclear Event Scale describes a level 7 event as a "major accident," in which a massive release of radioactive material causes widespread health and environmental effects, requiring planned and extended countermeasures.
NISA said Tuesday it estimated that radioactive materials measuring 370,000 terabecquerels have been released from the Fukushima plant.
The Nuclear Safety Commission of Japan, another government panel of experts, separately estimated the amount at 630,000 terabecquerels.
Either way, the amount far exceeds the INES level 7 standard of tens of thousands of terabecquerels.
In Chernobyl, radioactive materials released into the environment reportedly totaled some 5.2 million terabecquerels.
Nishiyama also pointed out that the reactor itself exploded in the Chernobyl accident, causing the widespread release of radioactive materials. At Fukushima, hydrogen explosions blew up two of four reactors' outer buildings, but it is believed the main containment vessels - the last defense of the reactors - largely remain intact at three of the four troubled reactors.
In Chernobyl, workers were unable to go near the site because of the high radiation levels. However, workers in Fukushima are operating around the clock, which proves that radiation there is significantly lower, Nishiyama added.
But Junichi Matsumoto, a spokesman for Tokyo Electric Power Co., was not so confident, saying he was concerned that the amount of radioactive materials may exceed Chernobyl in the end if Tepco fails to contain the ongoing crisis.
"Level 7 indicates a massive amount of radioactive leakage. We deeply apologize to residents around the plant and Fukushima Prefecture and society for causing concerns and troubles," he said.
Trade and industry minister Banri Kaieda, who oversees NISA, said most of the radioactive leakage has been due to the hydrogen explosions that occurred within the first few days after the twin natural disasters.
Kaieda said the government currently does not foresee any sharp spikes in radioactive discharge outside the plant compound for now.
"The most pressing issue at the moment is to prevent further (hydrogen) explosions from taking place and to curb the spread of radioactive materials . . . and currently, we do not expect to see a drastic increase in the mission," Kaieda said.
The estimates, however, only cover release by air, meaning the figure is likely to rise if leakage into the sea is included in the calculations. NISA said it will conduct a separate investigation on how much radioactive materials have been released into the Pacific Ocean.
Asked why NISA did not come forward with the data earlier if most of the release was made days after the disaster hit, Nishiyama said the agency wanted to gather a certain amount of data to make sure before making any assessment.
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