TEPCO, the utility in charge of the damaged Fukushima Daiichi nuclear power plant, has said that eight site restoration workers have received a combined internal/external dose of more than 250 mSv, the Japanese maximum dose rate for emergency operations.
It has also said that the two worst-affected male TEPCO employees had radioactive dose rates of 678 and 643 mSv caused by iodine 131. Two-thirds of the dose was from internal exposure. Medical examinations have found no health problems so far.
A total of 3726 people worked on the site since March, about two-thirds contractors and one-third TEPCO staff. Generally speaking TEPCO employees received a greater dose. In addition to the eight people who have received a dose over 250 mSv, a total of 94 people have received a dose over 100 mSv, according to a TEPCO report sent to the government. In terms of external dose only, average TEPCO employee dose was 13 mSv, almost double that of contractors (7.3). TEPCO has planned that employees with a dose rate over 20 mSv will receive a whole body counter scan and a reevaluation of their working conditions with interview.
On site, TEPCO staff and contractors have visited the third floor of the unit 4 Fukushima Daiichi reactor building to assess conditions for installing an alternative spent fuel pond cooling system (estimated to start operation in mid-July).
TEPCO has started up a forced-air filtration system inside the unit 2 reactor building to reduce the amount of radioactive dust and improve working conditions so that workers can install gauges and equipment to help bring the reactor to cold shutdown.
A test of the treatment system for contaminated water on site hit a design problem with flow rate problems caused by a valve control in the caesium adsorption tower section. Although the problem has been fixed, it will delay start-up of the entire system to allow for further testing.