Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake (Daily Report as of 3:00 PM on June 10)

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 Fukushima Daiichi Nuclear Power Station.

* 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 radiation dose 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.

<Measures to prevent expansion of contaminated water leakage>
On June 9, the leaked water accumulated in the leakage detection holes of the underground reservoirs No.1-3 and in the drain hole of the underground reservoir No.2 was transferred to the notch tank.

 

<Sampling>
On June 9, 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 of the analysis, no significant change was found compared to the analysis results from the sampling performed previously (on June 8).

-At 6:11 PM on June 9, a decrease was seen in the amount of water injected into the Unit 3 Reactor, and we adjusted the amount as follows:
The amount injected from the feed water system was increased from approx. 1.8m³/h to approx. 2.0m³/h, and the amount injected from the reactor core spray system was increased from approx. 3.3m³/h to 3.5m³/h.^*1

-At 6:25 AM on June 10, operation of the Unit 2 spent fuel pool alternative cooling system was suspended due to inspection on instruments of the cooling system (the pool water temperature was 22.9°C at the start of the suspension). The cooling-system suspension period is planned to be about 111 hours and the pool water temperature is expected to increase at a rate of 0.182°C/h. It is therefore expected that the water temperature will stay sufficiently far from the operational limit value of 65°C, and that there will be no problem in controlling the water temperature of the spent fuel pool.

-At 10:00 AM on June 10, accumulated water transfer from the Unit 6 Turbine Building basement to the temporary tank was started. At 3:00 PM on the same day, the transfer was stopped.

-At 10:50 AM on February 15, while carrying goods out of the large carry-in entrance in Unit 6 Reactor Building with its inside door (the door which opens by lifting up) open and its outside door closed, the inside door fell. The door which fell did not fall over. No injury due to the incident was reported and the incident did not affect the plant condition. Based on the investigation carried out for more information on the falling, we found out the following: During the electrical work at Unit 6, a worker tried to open the inside door of the large carry-in entrance of the Reactor Building in order to carry equipment out of the building; as the limit switch failed while the inside door was opening (going up), the worker tried to close the door using the manual operation button; however, since the inside door did not stop going up (opening), the worker turned off the power to stop the inside door; and, although the inside door stopped going up, it was found to have fallen down to the floor later on. Upon site investigation, no damage was found on the floor and the peripheral equipment although the inside door was damaged. Also, the joint part between the inside door and the chain for lifting the inside door up and down was found damaged.
As a result of the cause investigation of the falling, we determined that the inside door was caused to fall down to the floor because a malfunction occurred to the controller for stopping the hoisting device due to its internal deterioration and caused excessive winding up and consequent break of the suspension part of the chain for lifting the inside door up and down. Considering that the inside door was checked about operation but was not inspected in detail after having been out of use for about 2 years until March 1, 2012 when the operation was resumed, we will implement the following measures regarding the inside door as soon as the preparation is completed:
·Replacement of the control board with a new one
·Detailed inspection to be conducted when the inside door is used after having been out of use for a long time period

Together with the replacement of the control board with a new one, we will add the following functions:
·Excess winding-up prevention function in the hoisting device
·Overload stop function
·Installation of an emergency stop button

* Revised past progress

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