Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake(Daily Report as of 3:00 PM, May 17)

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). 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 radiationdose 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 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 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.

<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.
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. At 5:12 AM on April 29, the transfer was suspended. The amount of water transferred during the period from April 25 to 29 is approx. 4,600m³.
At 9:23 AM on April 29, the contaminated water transfer from the underground reservoir No.1 to H2 area tank was restarted. The water transfer was stopped at 12:19 PM on May 6. The total amount of transferred water during the period from April 23 to 26 and from April 29 to May 6 is approx. 2,250m³.

<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 May 16, the leaked water accumulated in the leakage detection holes of the underground reservoirs No.1 and 2 and in the drain hole of the underground reservoir No.2 was transferred to the notch tank. In addition, work to return the leaked water accumulated in the leakage detection hole of the underground reservoir No.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.
On April 7, sampling in the drain holes (northeast, southwest) and the leakage detection holes (northeast, southwest) of the underground reservoirs No.1-7 was started.
On April 10, sampling in the groundwater bypass pump wells No.1-4 was started.
On 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.
On April 15, sampling in the observation hole (A8) of the underground reservoir was started.
On April 17, sampling in the observation holes (A11, A18) of the underground reservoir was started.
On April 21, sampling in the observation holes (A9, A10, A12, A14, B1 and B2) of the underground reservoir was started. On 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.
On 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.
On April 24, sampling in the observation holes of the underground reservoirs (A1, A6, A7 and A17) and the observation hole on the sea side ((4)) was started.
On April 29, sampling in the observation holes on the sea side ((5), (6)) was started.
On April 30, sampling in the observation hole on the sea side ((8)) was started.
On May 1, sampling in the observation hole on the sea side ((7)) was started.
On May 8, sampling in the observation holes of the underground reservoir No.2 (2-3, 2-4) was started.
On May 10, sampling in the observation holes of the underground reservoir No.2 (2-1, 2-2) was started.
On May 12, sampling in the observation holes of the underground reservoir No.2 (2-5, 2-6, geological survey hole (1)) was started.
On May 13, sampling in the observation hole of the underground reservoir No.2 (2-7) was started.
On May 16, sampling was performed in the drain holes of the underground reservoirs No.1-7 (14 locations), the leakage detection holes of the underground reservoirs No.1-4 and 6 (sample could not be collected at 2 out of 10 locations) and the observation holes of the underground reservoirs (22 locations). As a result, no significant change was found with the results compared to the previous analysis results (May 15). Though the all β density in the leakage detection hole (northeast) of the underground reservoir No.1 had slightly increased (to 2.1x10³Bq/cm³) on May 15, the density has decreased to 9.2x10²Bq/cm³ on May 16 which is equivalent to the concentration on May 14 (7.2x10²Bq/cm³).

- At around 8:55 AM on May 17, a TEPCO employee preparing for yard watering found water overflowing from the upper part of Units 5-6 RO treated water tank. The leakage stopped after closing the valve at 9:00 AM on the same day. As a result of site inspection, the leakage area was found to be about 3m x about 20m. The leakage amount is estimated to be 27.5m³ based on the water levels of the D7 tank up to May 16 and the transfer amount of treated water. The water leaked from D7 tank is usually scattered within the power station site and the γ density and all β density of the water were below the detection limits (based on the sampling results obtained on May 16) (Cesium 137 detection limit: 1.5x10^-3Bq/cm³, All β detection limit: 2.3x10^-2Bq/cm³). As a result of sampling performed on May 17 to ensure safety, the γ density and all β density of the water were below the detection limits (Cesium 137 detection limit: 1.5x10^-3Bq/cm³, All β detection limit: 2.4x10^-2Bq/cm³). The leaked treated water has been absorbed into the ground. We consider that the leaked water will not flow into the sea because there are no side ditches near the location of the leakage, and because the source of the leakage is more than 100 m away from the sea. The treated water leakage was caused by overflow from the D7 tank, which is attributed to a failure to perform an operation to switch tanks from the D7 tank to the D8 tank, among eight treated water tanks (D1-D8) in total, while this operation was to be performed on May 16.

- At 9:44 AM on May 9, Unit 6 spent fuel pool cooling system was suspended for an inspection of the inlet/outlet valves of the component cooling system heat exchanger (A) (Pool water temperature when the system was suspended: 15.8℃). An alternating operation between the shutdown cooling system (for cooling the reactor) and the emergency heat load operation (for cooling the spent fuel pool) of the residual heat removal system has been started. At 10:05 AM on May 17, the auxiliary seawater pump was started as the inspection had been completed. The alternating operation between the shutdown cooling system (for cooling the reactor) and the emergency heat load operation (for cooling the spent fuel pool) of the residual heat removal system which had been ongoing during suspension was stopped after the recovery of the auxiliary seawater system. At 12:30 PM on the same day, the fuel pool cooling system was started and the spent fuel pool cooling is now being performed as usual. The pool water temperature as of 12:30 PM on the same day was 25.5℃.

- It has been confirmed that the hydrogen concentration and noble gas (Krypton 85) concentration (measured by Unit 2 PCV gas control system) tend to increase when the pressure inside the PCV dry well decreases. The incident is considered to be due to the hydrogen and noble gas (Krypton 85) accumulated in the upper part of the suppression chamber being discharged into the dry well through the vacuum breaker. From May 14 to May 17 (for about 6 hours per day), nitrogen injection into the upper part of the suppression chamber was performed in order to confirm the accumulated hydrogen and krypton 85. During nitrogen injection, the hydrogen concentration inside the dry well was monitored by the PCV gas control system. As a result, no change was found with the hydrogen concentration inside the dry well.

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

* Revised past progress

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