Further scrutiny of steam escaping from unit 3 this week revealed high radiation levels nearby, while revised estimates by Tokyo Electric Power Co. showed it significantly underestimated the number of workers who exceeded thyroid dose limits.
Recent developments related to TEPCO's damaged nuclear plant in Fukushima, Japan, include:
More Steam, High Radiation at Unit 3
Steam was spotted outside unit 3 again Wednesday after cameras captured similar puffs of steam July 18. Steam has not normally been present outside buildings at Fukushima Daiichi since its reactors were brought under control, and TEPCO believes it was caused by rainwater evaporating off unit 3's containment structure. A TEPCO release Wednesday reported that monitoring stations at the plant's perimeter did not detect an increase in radiation, and conditions inside the reactor were unchanged. Near the steam's source, the Asahi Shimbun reported, the company measured radiation at 562 millisieverts per hour. Other measurements on the fifth floor of the reactor building varied between 137 millisieverts per hour and 2,170 millisieverts per hour.
1,973 Workers Exceeded 100-Millisievert Thyroid Dose Threshold
Following skepticism by the U.N. Scientific Committee on the Effects of Atomic Radiation and other outside groups, TEPCO reevaluated an earlier study on worker thyroid doses and found 1,973 workers had exceeded the 100 millisievert level understood to increase cancer risk. A study released in December put the number of such workers at 178 before the new study expanded the number of subjects and research methodology. The Asahi reported TEPCO will pay for lifetime annual thyroid gland tests for workers with doses exceeding 100 millisieverts. Most worked at the plant early in the crisis and were exposed to radioactive contaminants through inhalation.
On Saturday, crews finished construction of a cover and adjacent structure for unit 4 that will eventually facilitate fuel removal.