June 3, 2011
The amount of radioactive materials released in the first days of the Fukushima nuclear disaster was almost two and a half times the initial estimate by Japanese safety regulators, the operator of the crippled plant said in a report released on Thursday.
The operator, the Tokyo Electric Power Company, said the meltdowns it believes took place at three reactors at the Fukushima Daiichi plant released about 900,000 terabecquerels of radioactive substances into the air during March 2011. The accident, which followed an earthquake and a tsunami, occurred on March 11.
The latest estimate was based on measurements suggesting the amount of iodine-131 released by the nuclear accident was much larger than previous estimates, the utility said in the report. Iodine-131 is a fast-decaying radioactive substance produced by fission that takes place inside a nuclear reactor. It has a half-life of eight days and can cause thyroid cancer.
It is difficult to judge the health effects of the larger-than-reported release, since even the latest number is an estimate, and it does not clarify how much exposure people received or continue to receive from contaminated soil and food. Experts have been divided on the health impacts since the disaster because the studies of assessing radiation risks are based mainly on a different type of exposure — the large doses delivered quickly by the atomic bombs in Japan in 1945.
Although people who lived closest to the plant were evacuated, many people remain in areas with significantly higher radiation levels than normal.
Tokyo Electric said it had initially been unable to accurately judge the amount of radioactive materials released soon after the accident because radiation sensors closest to the plant were disabled in the disaster.
“If this information had been available at the time, we could have used it in planning evacuations,” a spokesman for Tokyo Electric, Junichi Matsumoto, said at a news conference.
More than 99 percent of the radiation released by the accident came in the first three weeks, the utility company added.
The newly released information is likely to add to concerns among many Japanese that they were never told the extent of the accident or the risks it posed.
A terabecquerel is a trillion becquerels, a commonly used measure of the radiation emitted by a radioactive material.