Radiation dose measurements taken near a tank storing contaminated water at the Fukushima Daiichi site are up to 18 times higher than previously reported, according to measurements taken by Japanese utility TEPCO on 31 August.
The local radiation dose rate was measured at 1800mSv/hour at the bottom of Tank No. 4 in the H3 area on 31 August, according to TEPCO. This compares with a reading of around 100 mSv/hour in the same location on 22 August.
TEPCO said that most of the 1800 mSv/hour was beta radiation with gamma radiation measured at just 1 mSv/hour. As such, it said that radiation levels can be "reduced considerably by maintaining a distance" and that "radiation exposure can be controlled by the using proper equipment and clothing." TEPCO also noted that the reading was taken only a short distance (5cm) off the ground and said that the radiation level at 50 cm above the floor was 15 mSv/hour.
The dose rate measured near the bottom flange of Tank No. 10 in the same area was 220 mSv/hour on 31 August, around three times higher than in the same location a week earlier, according to TEPCO.
TEPCO said it considers there has been no leakage outside of the dike because the water levels of all of the relevant tanks have not decreased and the drainage valves have been closed.
It also confirmed that there has been "no continuous water dropping," in the H3 and H4 tank areas, but that it would conduct detailed investigations as to whether there has been water leakage.
On 19 August, TEPCO discovered that around 300 cubic meters of water had leaked from the drain valve in a dike surrounding tanks of contaminated water. Since then it has stepped up its inspections of the hundreds of tanks on site.
Photo: The radiation dose measumrents taken near Tank No. 4 increased from 100 mSv/hour on 22nd August to 1800 mSv/hour on 31 August (Source: TEPCO)