At around 9:30 am on April 2, 2011, we detected water containing radiation
dose over 1,000 mSv/h in the pit*1 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 flowing out to the ocean. At around 12:20 pm on April 2, we
reaffirmed the event at the scene.
We have implemented sampling of the water in the pit of Unit 2, together
with the seawater in front of the bar screen near the pit of Unit 2. These
samples were sent to Fukushima Daini Nuclear Power Station for analyses.
At around 5:38 am on April 6, we observed stoppage of spilling of water to
the ocean from the crack on the concrete lateral of the pit.
Since April 5, we have been conducting sampling surveys of the water in
the pit of Unit 2 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, and for
the other nuclides, we will re-evaluate them.
On April 12, 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 17, 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.
On May 11, 2011, responding to out-flow leakage of contaminated water from
the intake canal of Unit 3, from May 12th, we additionally conducted the
sampling of the seawater inside and outside of the silt fence in front of
the bar screen near the pit of Unit 1, 3 and 4.
On December 3, 2011, we conducted sampling*2 of the seawater near the
intake canal of Units 1 to 4 of Fukushima Daiichi Nuclear Power Station
and analyzed the samples. As a result, some radioactive materials were
detected as described in the appendix.
We reported the above results to NISA as well as to the government of
Fukushima Prefecture today.
We will continuously conduct the same sampling surveys.
*1 Pit: vertical shaft made of concrete
*2 From November 15, 2011, in order to prevent deterioration of pumping
function by sucking in sand etc., we are cleaning the bottom of
auxiliaries water intake pump room, Units 5 & 6. In order to evaluate
the impact on the surrounding environment, we increased sampling points.
Appendix1: Nuclide Analysis Results of Radioactive Materials in Seawater
Fukushima Daiichi Nuclear Power Station; the shallow draft quay,
Unit 1-4 screen, and the water intake canal of Units 1-4
Appendix2: Nuclide Analysis Results of Radioactive Materials in Seawater
in the water intake, Units 5 & 6, Fukushima Daiichi NPS
Appendix3: Radioactivity Density of Seawater (PDF 43.4KB)