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
-A worker of TEPCO confirmed a decrease in the amounts of water injection for Unit 1 - 3 reactors as below at 3:00 PM on August 30 at the regular data check.
Unit 1: The amount of water injection decreased from 4.9m3/h (at 2:00 PM) to 4.0m3/h.
(The required amount of water injection: 4.3m3/h.)
Unit 2: The amount of water injection decreased from 7.0m3/h (at 2:00 PM) to 5.5m3/h.
(The required amount of water injection: 6.1m3/h.)
Unit 3: The amount of water injection decreased from 7.0m3/h (at 2:00 PM) to 5.6m3/h.
(The required amount of water injection: 6.1m3/h.)
The shift supervisor judged that the condition did not satisfy the "Operational Requirements" defined by the Technical Specification" for Unit 2 at 3:00 PM, for Unit 3 at 3:05 PM and for Unit 1 at 3:07 on the same day. Though we attempted to increase the water injection amounts at the site, the amounts kept decreasing. The water injection amounts were continuously monitored and have been adjusted as necessary. As a result of site investigation, no water leakage from the reactor injection system was found. Upon checking the regular reactor injection water pump on the hill (B) and (C) which were in operation when the injection amounts started decreasing, no air intrusion was found in the pumps.
Since there was a possibility of dust or substance attached to the flow rate adjustment valves, flushing was done on these valves on August 31.
(The required amounts of water injection for each unit were changed as follows on September 1. Unit 1: 3.8m3/h, Unit 2: 5.4m3/h, Unit 2: 5.4 m3/h)
On September 2, the opening amounts of the flow rate adjustment valves were increased to prevent substances from being attached on them as a part of investigating the cause of the flow rate decrease. The injection water amounts are continuously monitored and adjusted as necessary.
From 11:55 AM to 1:00 PM on September 4, the spool installed on the inlet side of the regular reactor injection water pump on the hill (C) on stand-by was removed for inside inspection. From 12:00 PM to 12:50 PM, investigation on the substances attached on the strainers installed at the entrance of the refrigerators used for buffer tank water cooling (2 out of 6 refrigerators). Though no substance was found inside the inlet pipe of the regular reactor injection water pump on the hill (C), some (brown and white) were found on the strainers installed at the entrance of refrigerators for buffer tank water cooling. On September 5, a camera was inserted into the buffer tank from the man hole above the buffer tank and white suspended materials were found in the tank as a result. On September 6, the substances attached on the filter used for buffer tank water sampling were analyzed, and it was found that the metal composition of the substances was mostly iron, which is of no risk. From around 9:32 AM on September 8, purification of the buffer tank water (to eliminate the suspended materials in it) was started using an underwater pump. At 1:40 PM on the same day, the purification was completed.
As the injection water amounts kept decreasing since the previous report (at 3:00 PM on September 7), the amounts were adjusted as below.
At 3:23 PM on September 7
[Unit 1] Feed water system: Decreased from 3.1m3/h to 3.0m3/h, Reactor core spray system: Increased from 1.6m3/h to 2.0m3/h (In total, the amount was increased from 4.7m3/h to 5.0m3/h)
[Unit 2] Feed water system: Increased from 1.4m3/h to 2.0m3/h, Reactor core spray system: Decreased from 5.5m3/h to 5.0m3/h (In total, the amount was increased from 6.9m3/h to 7.0m3/h)
[Unit 3] Feed water system: Increased from 2.0m3/h to 2.5m3/h, Reactor core spray system: Decreased from 4.9m3/h to 4.5m3/h (In total, the amount was increased from 6.9m3/h to 7.0m3/h)
We will continue to investigate on the cause of this matter and monitor the water injection amounts. No significant change has been found with the bottom of RPV of each unit, other plant parameters and the monitoring post data.
-At around 12:00 AM on September 4, a high rate of temperature increase (step-like increase by 1.6°C) was detected on Unit 2 RPV bottom temperature monitoring thermometer (Included in the technical specification (Article 138/143) watch list, VESSEL BOTTOM ABOVE SKIRT JOT (TE-2-3-69F2)). Due to this, a direct current resistance measurement was performed on the thermometer from 11:15 AM to 11:24 AM on September 6. As a result, the direct current resistance (209.34Ω) was found to be 30% or more compared to the minimum direct current resistance measured after the accident (117.84Ω). A temperature trend evaluation (secondary evaluation) will be done to determine whether the thermometer will be used as a reference thermometer or judged to be broken. As a result of a temperature trend evaluation (secondary evaluation), the thermometer was excluded from the technical specification watch list and has been designated as a reference thermometer.
-As a flow rate decrease was found with Unit 5 residual heat removal system seawater pump A, the pump was switched from A to C from 1:25 PM to 1:27 PM on September 7. The residual heat removal system (A) and the residual heat removal system seawater pump C were stopped at 4:35 PM and 4:37 PM respectively on the same day to investigate the cause of the performance degradation of the pump A and conduct an operation check on the pump A (Reactor water temperature when the system was stopped: 30.9°C). At 4:42 PM on the same day, the residual heat removal system seawater pump A was started. As the flow rate had recovered almost up to the level at the time of the trial operation and the differential pressure of the heat exchanger was also secured, continued operation of the pump A was determined. At 5:50 PM on the same day, the residual heat removal system (A) was started (Reactor water temperature when the system was started: 31.9°C). As a flow rate decrease was found again with the residual heat removal system seawater pump at 6:56 AM on September 8, the pump C was started at 7:10 AM and the pump A was stopped at 7:13 AM on the same day. When the pump A was restarted at 11:21 AM and the pump C was stopped at 11:28 AM on the same day, the flow rate of the pump A was above the control value. However, as the margin to the control value was judged to be insufficient, the pump C was restarted at 11:48 AM and the pump A was stopped at 11:51 AM on the same day. The pump A will be inspected and a trial operation will be conducted.
-At 10:19 AM on September 6, we started transferring the accumulated water in Unit 4 Turbine Building basement to the Central Radioactive Waste Facility (Miscellaneous Solid Waste Volume Reduction Treatment Building [High Temperature Incinerator Building]). At 2:01 PM on September 8, the transfer was stopped. At 2:11 PM on the same day, the transfer was restarted.
[ Fukushima Daini Nuclear Power Station ]
·Unit 1 to 4: Shutdown due to the earthquake.
Appendix:
Past Progress (As of 3:00 pm, on September 8, 2012) (PDF 521KB)
Appendix:
Past Progress (From March 11, 2011 to December 31, 2011) (PDF 523KB)
*
Revised past progress
The aforementioned attachments are only available in Japanese.
We apologize for any inconvenience this may cause.
