The Japanese government may have underestimated by 20 percent the internal radiation doses in workers during the initial phases of the Fukushima No. 1 nuclear power plant disaster, a U.N. panel said.
The U.N. Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) raised doubts about the dose estimates of the Japanese government and Tokyo Electric Power Co., the plant operator, in a summary of a report submitted to the Fourth Committee of the U.N. General Assembly on Oct. 12.
UNSCEAR used data provided by the Japanese government, TEPCO and other entities to assess the amount of radioactive substances discharged during the nuclear crisis that began in March 2011. It also analyzed radiation doses in the 25,000 or so individuals who worked at the plant no later than October 2012.
The U.N. committee noted that workers were tested for thyroid gland doses from radioactive iodine only after a significant delay. It also said the dose assessment procedures totally ignored iodine-132 and iodine-133, which have short half-lives of 2 hours and 20 hours, respectively.
After assessing discharge volumes and their contribution to doses for each class of radioactive substance, UNSCEAR concluded that worker doses during the early stages of the nuclear crisis may have been underestimated by about 20 percent.
The government and TEPCO are providing free health checkups to Fukushima plant workers whose doses have reached certain levels.
Currently, about 1,100 individuals who received 50 millisieverts or more in whole-body doses can receive free tests for cancer of the thyroid gland, lungs, stomach and colon. About 2,000 people with whole-body doses below 50 millisieverts but thyroid gland doses of 100 millisieverts or more are qualified to be tested for thyroid gland cancer.
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