At around 9:30 am on April 2nd, 2011, we detected water containing
radiation dose over 1,000 mSv/h in the pit* where power supply cables are
stored near the intake channel of Unit 2. Furthermore, there was a crack
of about 20 cm length on the concrete lateral of the pit, from where the
water in the pit was outflowing to the ocean. At around 12:20 pm on April
2nd, we reaffirmed the event at the scene.
We have implemented sampling of the water in the pit, together with the
seawater in front of the bar screen near the pit. These samples were sent
to Fukushima Daini Nuclear Power Station for analyses.
At around 5:38 am on April 6th, we have observed stoppage of spilling of
water to the ocean from the crack on the concrete lateral of the pit.
Since April 5th we have been conducting sampling surveys of the water in
the pit and the seawater in front of the bar screen near the pit.
Regarding the survey results of the detection of three nuclides (iodine
131, cesium 134, cesium 137), we report those as definite results. As for
other nuclides, we will revaluate in accordance with the preventive
measures formulated after receiving a warning from Nuclear and Industrial
Safety Agency (NISA) on April 1st.
On April 12th, due to the installation of silt fences, we changed the
sampling points from the front of the bar screen of Unit 4 to the north
and the south of the inside of the water intake canal of Units 1 to 4.
Since April 17th, we have been conducting an additional sampling survey
outside the silt fence in front of the bar screen of Unit 2, in order to
assess the effect of the installation of the silt fence.
Apart from the daily sampling surveys, we have conducted the sampling
survey of the water in the upper and lower layer of the ocean inside the
silt fence in front of the bar screen of Unit 2 since May 5th.
On May 6th, 2011, we conducted the sampling survey of the water in the pit
and the seawater in front of the bar screen near the pit, and conducted
nuclide analysis of radioactive materials in the water. As a result, some
radioactive materials were detected as described in the exhibit.
Accordingly, we have reported the result of the analysis to NISA and the
government of Fukushima Prefecture.
We will continue to conduct the same kind of sampling surveys.
* pit: a vertical shaft made of concrete
Appendix1:Result of Nuclide Analysis of the seawater at the shallow draft
quay, Unit 2 screen, and the water intake canal of Unit 1-4
Appendix2:Radioactivity density of seawater (PDF 26.2KB)