Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake (Daily Report as of 3:00 PM, April 27)

Due to the Tohoku-Chihou-Taiheiyou-Oki Earthquake which occurred on March 11, 2011, TEPCO's facilities including our nuclear power stations have been severely damaged. We deeply apologize for the anxiety and inconvenience caused.
With regard to the accident at Fukushima Daiichi Nuclear Power Station, on April 17, 2011, we have compiled the roadmap towards restoration from the accident and on July 19 we accomplished the Step1 target "Radiation dose is in steady decline". Then on December 16 we confirmed the accomplishment of the Step 2 target "Release of radioactive materials is under control and radiation doses are being significantly held down".
In addition, on December 21, 2011, we have compiled the "Mid-to-long-Term Roadmap toward the Decommissioning of Fukushima Daiichi Nuclear Power Units 1-4, TEPCO".
In addition to the maintenance of the plant's stable condition, we will implement Mid-to-Long Term countermeasures towards the decommissioning of Fukushima Daiichi Nuclear Power Units 1-4 to enable evacuees to return to their homes as soon as possible and reduce the anxiety of the people in Fukushima and the whole nation as soon as possible.

Below is the status of TEPCO's nuclear power stations (Fukushima Daiichi and Fukushima Daini).

* The updates are underlined.

[Fukushima Daiichi Nuclear Power Station]
·Unit 1 to 4: Abolishment (April 19, 2012)
·Unit 5 to 6: Outage due to regular inspections before the earthquake

-As for the underground reservoir No.2 installed within the power station site, 10¹Bq/cm³ level of radiation was detected as a result of analyzing the water accumulated between the sheet on the outside (bentonite sheet) and the ground (the underground reservoir is made of three layers of impermeable sheets) on April 3. On April 5, radiation was detected in the water between the sheet on the outside (bentonite sheet) and the sheet on the inside (double-layered permeable sheet) as a result of analysis. The radioactivity density of all β detected was approx. 5.9×10³Bq/cm³. Considering that there is no drain ditch in the surrounding area, it is considered that there is no possibility of the leaked water flowing into the sea. At 5:10 AM on April 6, the incident was judged to be a leakage which is subject to the application of Article 19-17, Item 10 of the Rule for the Installation, Operation, etc. of Commercial Nuclear Power Reactors (Rule for Commercial Nuclear Power Reactors). At 5:43 AM on April 6, we started transferring the water stored in the underground reservoir No.2 to the underground reservoir No.1 utilizing a permanent pump. Considering that the amount of leaked water is approx. 120m³, all γ radioactivity density is approx. 1.5×10⁰Bq/cm³ and all β radioactivity density is approx. 5.9×10³Bq/cm³, the γray radiation dose leaked is estimated to be approx. 1.8×10⁸Bq and the β radiation dose leaked is estimated to be approx. 7.1×10¹¹Bq. Details are currently being investigated.
While enhancing the monitoring of the water level of the underground reservoir No.3, on April 7, sampling was performed on the water in the drain hole (southwest) and the leakage detection hole (southwest) of the underground reservoir No.3 for the purpose of investigating the leakage location.
Considering that all β nuclides were detected in the water in the leakage detection hole and the drain hole of the underground reservoir No.3 as a result of sampling, it was judged at 8:53 AM on the same day that there may be a small amount of leakage from the impermeable sheet on the outside (bentonite sheet) of the reservoir to the outside.
The samples collected in the morning of April 9 in the drain hole (at 2 locations) and the leakage detection hole (at 2 locations) of the underground reservoir No.1 have been analyzed. As a result, the chloride concentration of the water in the leakage detection hole (northeast) has increased from 4ppm (on the previous day) to 910ppm. At 12:47 PM, water transfer from the underground reservoir No.2 to No.1 utilizing temporary pumps was suspended. Considering that all βnuclides were detected as a result of sampling performed in the leakage detection hole of the underground reservoir No.1 for the purpose of investigating the leakage location, it was judged at 4:34 PM on the same day that there may be a small amount of leakage from the sheet on the inside (double -layer impermeable sheet) to the impermeable sheet on the outside (bentonite sheet) of the reservoir although the water level of the underground reservoir No.1 has not decreased and the analysis results of the drain hole water of the underground No.1 have not yet been confirmed.
On April 10, the soil covering the leakage detection hole (northeast) penetration of the underground reservoir No.2 was removed to perform a visual inspection of the penetration. The removal of the impermeable sheet, gravels, etc. will be continued. Furthermore, drilling work was started for the boring investigation to confirm the contamination condition of the surrounding area of the underground reservoirs and contamination expansion to the sea side. The work will be continued. Though water transfer from the underground reservoir No.3 to No.6 was started at 2:00 PM on the same day, the transfer pump was stopped at 2:03 PM as water leakage from the connection part (flange) of the transfer pump outlet pipe was found. The leakage stopped after stopping the transfer pump. The pipe flange was disassembled for cause investigation. As a result, the cause was identified to be the problem with the flange connection part (inhomogeneous amount of gap on the surfaces). The flange was recovered after replacing the gasket. Since no problem was found as a result of measuring the gaps on other flanges and checking the tightening condition of the flange bolts, the water transfer was started at 9:56 PM on April 12. As for the removal of the soil covering the upper part of the reservoir (embankment) where the leaked water is assumed to have been absorbed, further drilling was performed (a total of the drilling depth: 30-60cm) and the radioactivity density on the ground surface has been reduced down to 0.05mSv/h (β＋γ) (max.). At 3:06 PM on April 14, the water transfer from the underground reservoir No.3 to No.6 was suspended as the transfer of the planned water amount had completed.
On April 12, sampling was performed in the drain holes of the underground reservoirs No.1-7 (at 14 locations) and the leakage detection holes of the underground reservoirs No.1-4 and 6 (sample could not be collected at 2 out of 10 locations). As a result, the all β density in the drain hole (northeast) of the underground reservoir No.1 was found to have increased during the period from April 10 to 12. Thus, it was judged that there has been a small amount of leakage from the sheet on the outside (bentonite sheet) to the outside. Since there is no drainage in the surrounding area, there is no possibility that the leaked water has flowed out to the sea.
On April 19, the filtrate water tank No.1 was detached from the transfer line between the buffer tank and the filtrate water tanks No.1/No.2^* in order to prepare for the water transfer from the underground reservoir No.1 to the filtrate water tank.
*Since the water supply from the filtrate water tank (emergency water supply for the reactor water injection system) was disabled during the work, Article 136, Section 1 of the technical specification (intentional transition out of the scope of operational requirement for maintenance work) was applied to the period from 8:30 AM to 11:01 AM on April 19.
Though filtrate water supply from the filtrate water tank was disabled during the work, there was no impact on the reactor water injection as the freshwater treated by the water treatment facility was supplied to the buffer tank. Considering that there are raw water tanks in addition to the filtrate water tanks prepared for emergency use, the amount of water required for the buffer tank was confirmed to be available.

<Transfer of water stored in the underground reservoirs>
From April 6 to April 9, contaminated water was transferred from the underground reservoir No.2 to No.1.
From April 6 to April 11, contaminated water was transferred from the underground reservoir No.2 to No.6.
From April 11 to April 14, contaminated water was transferred from the underground reservoir No.3 to No.6.
From April 16 to April 22, contaminated water was transferred from the underground reservoir No.2 to H2 area tank. The amount of water transferred during the period is approx. 1,070m³.
At 12:24 PM on April 23, contaminated water transfer from the underground reservoir No.1 to H2 area tank was started. The transfer will be temporarily suspended after the transfer performed on April 26. After the contaminated water transfer from the underground reservoir No.1 to the filtrate water tank No.1 is complete, the contaminated water transfer from the underground reservoir No.1 to H2 area tank will be restarted.

At 10:58 AM on April 25, contaminated water transfer from the underground reservoir No.1 to the filtrate water tank No.1 was started.

<Measures to prevent expansion of contaminated water leakage>
Since April 10, work to return the leaked water accumulated in the leakage detection hole of the underground reservoir No.1 to the reservoir has been performed.
Since April 11, work to return the leaked water accumulated in the leakage detection hole of the underground reservoir No.2 to the reservoir has been performed.
Since April 13, work to return the leaked water accumulated in the leakage detection hole of the underground reservoir No.3 to the reservoir has been performed.
The measures to prevent expansion of contaminated water leakage are to be implemented for the underground reservoirs No.1-3 as necessary.
On April 26, work to return the leaked water accumulated in the leakage detection holes of the underground reservoirs No.1-3 to the reservoir was performed.

<Sampling>
On April 6, sampling was performed in the drain holes of the underground reservoirs No.1, 3 and 4 as well as in the drain holes (northeast, southwest) and the leakage detection holes (northeast, southwest) of the underground reservoir No.2.
Since April 7, sampling has been performed in the drain holes (northeast, southwest) and the leakage detection holes (northeast, southwest) of the underground reservoirs No.1-7.
Since April 10, sampling in the groundwater bypass pump wells No.1-4 was started.
Since April 11, sampling in the groundwater bypass investigation holes A-C was started.
On April 14, sampling was performed in the leakage detection hole (southwest) of the underground reservoir No.7 for background measurement.
Since April 15, sampling in the observation hole (A8) of the underground reservoir was started.
Since April 17, sampling in the observation holes (A11, A18) of the underground reservoir was started.
Since April 21, sampling in the observation holes (A9, A10, A12, A14, B1 and B2) of the underground reservoir was started.
Since April 22, sampling in the observation holes of the underground reservoirs (A3, A4, A15, A19 and B3) and in the observation holes on the sea side ((1) and (2)) was started.
Since April 23, sampling in the observation holes of the underground reservoirs (A2, A5, A13 and A16) and in the observation hole on the sea side ((3)) was started.
Since April 24, sampling in the observation holes of the underground reservoirs (A1, A6, A7 and A17) was started.
As a result of sampling performed in the observation holes of the underground reservoirs on April 26, all β with density slightly above the detection limit (approx. 2.8x10^-2Bq/cm³) was detected in 13 out of 22 observation holes of the underground reservoirs (Max: approx. 4.8×10^-2Bq/cm³). The analysis results are equivalent to those of the drain holes of underground reservoirs No.5 and 7 in which no water is stored. As a result of reanalyzing the same samples on April 27, all β with density slightly above the detection limit (approx. 3.0x10^-2Bq/cm³) was detected in 2 out of 22 observation holes of the underground reservoirs (A1, A4) (Max: approx. 3.7×10^-2Bq/cm³). The reason why the all β detected in the previous analysis was not detected this time is considered to be due to the fluctuation within the range of detection limit.
On April 26, sampling was performed in the drain holes of the underground reservoirs No.1-7 (14 locations) and the leakage detection holes of the underground reservoirs No.1-4 and 6 (sample could not be collected at 3 out of 10 locations). As a result, no significant change was found compared to the previous day (April 25).

-At 9:39 AM on April 25, Unit 3 spent fuel pool alternative cooling system was suspended in order to implement power supply duplication (pool water temperature when the cooling was suspended: 15.9℃). At 7:05 PM on April 26, the spent fuel pool cooling was restarted as the work had completed. Though the spent fuel pool water temperature increased to approx. 18.5℃, there is no problem with the spent fuel pool water temperature control considering that there is a sufficient margin to the maximum allowed temperature (65℃).

-At 9:50 AM on April 26, Unit 4 spent fuel pool alternative cooling system was suspended in order to implement power supply duplication (pool water temperature when the cooling was suspended: 25℃). At 6:15 PM on the same day, the spent fuel pool cooling was restarted as the work had completed. Though the spent fuel pool water temperature increased to approx. 26℃, there is no problem with the spent fuel pool water temperature control considering that there is a sufficient margin to the maximum allowed temperature (65℃).

-At 9:34 AM on April 27, the accumulated water transfer from Unit 2 Turbine Building basement to Unit 3 Turbine Building basement was started.

[Fukushima Daini Nuclear Power Station]
·Unit 1 to 4: Shutdown due to the earthquake.

* Revised past progress

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