Status of TEPCO's Nuclear Power Stations after the Tohoku-Chihou-Taiheiyou-Oki Earthquake(Daily Report as of 3:30 PM, April 6)

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

- At around 5:23 AM on April 4, the multi-nuclide removal equipment (ALPS) for which hot testing using waste liquid treated by the contaminated water treatment facility was being performed has been suspended due to incorrect operation. Since no abnormality was found as a result of site investigation performed after the incident, the treatment of water remaining in the system was started at 6:33 AM on the same day. No problem has been found with its operation after starting the treatment of the remaining water. At 6:54 PM on the same day, the treatment of water remaining in the system was completed. Since cause investigation and recurrence prevention measures have been implemented as below, the equipment was restarted at 7:18 PM on April 5. No problem was found with operation after restart.
[Cause investigation]
- An operator accidentally selected a wrong button on the panel (operation screen switching button) as the tip of the touch pen was too large.
- Though there was a time lag during screen transition, the operator kept touching the screen which led to the operation switch (on the screen after transition) selected by mistake. As a result, the multi-nuclide removal equipment was suspended.
[Recurrence prevention measures]
-Operation will be done using a mouse instead of a touch pen.
-Thoroughly remind operators to "make sure to perform each operation correctly" to prevent continuous selection of incorrect buttons.
-Put up a warning sign (including the above measures) near the console panel.
-Screen operation to collect data will be performed by a pair of operators to prevent single person operation. The supervisor responsible for the operation will also be clarified.
Furthermore, software modification will be implemented to allow for double action instead of single action for the switches related to equipment operation.

- At around 2:27 PM on April 5, an alarm indicating a power board failure related to power supply went off and Unit 3 spent fuel pool alternative cooling system was confirmed to be suspended. As a result of insulation resistance test performed on the power supply facilities affected by the suspension from 3:50 PM to 4:00 PM, no abnormality was found. From 4:16 PM, operation to restart the system was started. Considering that a countermeasure against small animals (installation of entry prevention net) was being implemented on the power board of the concerned system in response to the power supply failure occurred on March 18, there is a high possibility that a ground fault had occurred during the work. The secondary system and the secondary system cooling tower of the alternative cooling system were started at 4:55 PM and 5:00 PM respectively. As the primary system of the alternative cooling system was started at 5:20 PM, the entire system was restarted. No problem has been found with operation after restart. The spent fuel pool temperature after the restart (as of 6:10 PM on April 5) was 15.2℃. There is no problem with the pool water temperature control considering the sufficient margin to the maximum allowed temperature (65℃).

-At 6:29 PM on April 5, an alarm indicating an abnormality of the main equipment went off at the continuous dust monitor installed at the main gate. In response to this, an instruction to put on full-face mask within the power station site was given. At 6:42 PM on the same day, the equipment was recovered after resetting the alarm. As a result of investigating the continuous dust monitor, the alarm was confirmed to have gone off due to a temporary decrease in the sampling flow rate. Since no problem was found with the measurement of radioactivity density, the instruction to put on full-face mask was cancelled at 7:07 PM on the same day. As a result of measurement by a dust sampler, the radioactivity density was 8.2x10^-6Bq/cm³, which is of no problem

- As for the underground reservoir No.2 installed within the power station site on April 3, 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 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 5:43 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.
As three temporary pumps were added and no problem was found with the temporary water transfer line, we started transferring the water from the underground reservoir No.2 to No.1 at 9:38 AM on the same day. In order to add another temporary pump, the pumps other than the permanent pump (3 temporary pumps) were temporarily suspended at 12:27 PM on the same day. Since no problem was found with the temporary pipeline of the newly added temporary pump, the water transfer from the underground reservoir No.2 to No.1 was started at 12:52 PM. The three temporary pumps suspended were restarted at 12:57 PM for water transfer from the underground reservoir No.2 to No.1. The water stored in the underground reservoir No.2 will be transferred to the underground reservoir No.1 utilizing the four temporary pumps (approx. 30m³/h x 2, approx. 48m³/h, and approx. 60m³/h) which is planned to take about 2.5 days. The remaining water in the underground reservoir No.2 (approx. 3,000m³) is planned to be transferred to the underground reservoir No.6 by the permanent pump (approx. 40m³/h) which will take about 3.1 days. Since the transfer works above will be implemented in parallel, the number of days necessary for water transfer is estimated to be about 3.1 days.

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

*Regarding the multi-nuclide removal equipment (ALPS) which restarted operation on April 5, it said in the daily report previously announced that the equipment was restarted "at 7:18 PM on April 6", however, it has been corrected to "at 7:18 PM on April 5". We apologize for the mistake.

*The information on the alarm (indicating an abnormality of the main equipment) which went off at the continuous dust monitor at 6:29 PM on April 5 was not announced in the daily report previously announced. We apologize for the mistake.
* Revised past progress

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