Fukushima Daiichi NPS Prompt Report 2013

This is follow-up information on the "water leak at a tank in the H4 area in Fukushima Daiichi Nuclear Power Station" found on August 19.

We have intensified patrols on the tanks after finding the water leakage from the drain valve at the dike around the H4 area tanks. During a patrol today (on September 4), no location showed a high dose equivalent rate.

We conducted a visual inspection, which confirmed that there have been no abnormalities, neither leaks nor traces of leaks, at all of the tanks.

At the below-listed locations that have shown high dose equivalent rates, we implemented radiation shielding with sealing materials, acrylic boards and rubber mats yesterday (on September 3) on trial. Then, the dose equivalent rates decreased.

Today, dose measurement with the above radiation shielding in place was conducted in the patrol.

[Results of dose measurement (conducted on September 3)]
<Before radiation shielding implementation>
· Tank No.4 (north side) in Group B in the H3 area: 2,200mSv/h (at the 5-cm distance)^*1
· Tank No.4 (south side) in Group B in the H3 area: 500mSv/h (at the 5-cm distance)^*1
· Tank No.10 (north side) in Group A in the H3 area: 70mSv/h (at the 5-cm distance)^*1
<After radiation shielding implementation>
· Tank No.4 (north side) in Group B in the H3 area: 30mSv/h (at the 5-cm distance)^*1
· Tank No.4 (south side) in Group B in the H3 area: 15mSv/h (at the 5-cm distance)^*1
· Tank No.10 (north side) in Group A in the H3 area: 10mSv/h (at the 5-cm distance)^*1
*1: Values of 70μm dose equivalent rates (β ray)^*2
(Values of 1cm dose equivalent rates (γ ray) were less than 1mSv/h.)
*2: 70μm dose equivalent rate = dose equivalent rate to the skin, etc.