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 9:51 AM on November 26, we started transferring the accumulated water in Unit 4 Turbine Building basement to the Central Radioactive Waste Treatment Facility (Miscellaneous Solid Waste Volume Reduction Treatment Building [High Temperature Incinerator Building]).
-As a measure to prevent the increase of PCV/RPV ambient temperatures during the summer (prevent the increase of PCV/RPV ambient temperatures by cooling the water injected into the reactor), refrigerators for cooling the water in the treatment water buffer tank were installed. At 9:30 AM on July 18, trial operation of the refrigerators was started. As no issue was found with their operation, continuous operation was started at 3:20 PM on the same day. As the buffer tank water temperature has decreased according to the lower outdoor air temperature, the refrigerators were stopped at 10:15 AM on November 26 (the treatment water buffer tank water temperature when the refrigerators were stopped: 10.8°C).
-At 9:37 AM on October 23, continuous nitrogen injection into Unit 1 suppression chamber was started. As of 5:00 AM on November 26, the hydrogen concentration inside the PCV has decreased down to 0.18%. Since most of the residual hydrogen in the suppression chamber is considered to have been replaced, continuous nitrogen injection into the suppression chamber was stopped at 10:37 AM on the same day. Nitrogen injection will be performed again to let the residual gas out of the suppression chamber.
-At the regular plant parameter data check at 11:00 AM on November 26, a TEPCO employee found that Unit 3 reactor injection water amount had increased from 5.8m3/h (as of 10:00 AM on the same day) to 7.0m3/h (as of 11:00 AM). The technical specification for the nuclear reactor facility*1 stipulates that an increase amount of reactor injection water from the regular use reactor injection system must be 1.0m3/h or less during any given 24 hours as an "operational requirement"*2. Since the increase of Unit 3 reactor injection water exceeded 1.0m3/h, the shift supervisor on duty judged that the condition did not fulfill the "operational requirement" stipulated by the technical specification for the nuclear reactor facility at 11:00 AM on the same day. As the "required measure to be taken" for this incident is to start implementing measures to reduce the increase amount of reactor injection water down to the allowed range, the reactor injection water amounts at Unit 3 were adjusted as follows at 11:10 AM. Feed water system: Decreased from approx. 4.0m3/h to approx. 2.0m3/h, Reactor core spray system: Increased from approx. 3.0m3/h to approx. 4.0m3/h. Unit 3 PCV gas control system indicates no change in xenon 135 density which is below the detection limit (3.4×10-1 [Bq/cm3]) and subcritical. There has been no significant change in the monitoring post data and no leakage around the injection line between the regular use reactor injection system and the building entrance. The reactor injection water amounts at Units 1 and 2 remain stable. The cause of the incident is currently under investigation.
*1 Technical specification for the nuclear reactor facility
Government-approved fundamental rules for nuclear power station operators to follow in order to maintain safe operation and stable condition of nuclear power stations (including operation management, fuel management, radiation management, emergency measures and equipment/facility management based on the "Policy on the Mid-term Security"), which are stipulated by Article 37 Section 1 of the Act on the Regulations of Nuclear Source Material, Nuclear Fuel Material and Reactors.
*2 Operational requirements
In accordance with the technical specification for the nuclear reactor facility, operational requirements are stipulated to ensure safety and stability of power stations (such as the number of available equipments, temperatures and pressures). In the case that an issue arises with equipment subject to the technical specification and the operational requirements cannot be satisfied temporarily, appropriate measures must be implemented.
-From 2:42 PM to 2:44 PM on November 11, Unit 5 residual heat removal system seawater pump in operation was switched from (C) to (A) since the flow rate of pump (C) had decreased. At 8:31 AM on November 20, the residual heat removal system (A) was stopped to have all the residual heat removal system seawater pumps temporarily suspended in order to inspect and repair the residual heat removal system seawater pump (C) (the reactor water temperature when the system was stopped: 31.7°C). At 12:09 PM on the same day, the residual heat removal system (A) was restarted (the reactor water temperature when the system was restarted: 33.8°C). At 6:01 AM on November 26, the component seawater system was stopped in order to investigate the floor surface where the residual heat removal system seawater pumps (A) and (C) are installed with an underwater camera (the pool water temperature when the system was stopped: 18.8°C). At 9:00 AM on the same day, the residual heat removal system (A) was stopped (the reactor water temperature when the system was stopped: 33.6°C) and the system was started at 1:14 PM on the same day (the reactor water temperature when the system was started: 35.8°C). At 1:31 PM on the same day, the component seawater system was started (the pool water temperature when the system was started: 20.0°C). There is no problem with the reactor water temperature control considering the sufficient margin to the maximum allowed temperature (100°C). There is also no problem with the spent fuel pool water temperature control since there is a sufficient margin to the maximum allowed temperature (65°C).
[Fukushima Daini Nuclear Power Station]
・Unit 1 to 4: Shutdown due to the earthquake.
Appendix:
Past Progress (As of 3:00 pm, on November 26, 2012) (PDF 605KB)
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.
