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 0:20
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.
For the sake of completeness, we put further reinforcement for the
stoppage of leakage and consider countermeasures including continuous
injection of coagulant. We also note the water level of the turbine
building of Unit 2 remains unchanged. We will further investigate if
there is any other leakage.
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
at the outside of 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.
On April 24th, 2011, we collected samples from the water in the pit and
the seawater in front of the bar screen near the pit, and conducted
nuclide analyses 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 analyses to NISA and
the government of Fukushima Prefecture.
* pit: a vertical shaft made of concrete
Appendix: Result of Nuclide Analysis of the seawater at the shallow draft
quay, Unit 2 screen, and the water intake canal of Unit 1-4
Appendix: Radioactivity density of seawater(PDF 41.8KB)