On March 11 2011, Fukushima Daini Nuclear Power Station Units 1 to 4 
(Boiling Water Reactors, rated output 1,100 Megawatts each) that we had 
been operating at rated thermal output shutdown automatically at 2:48 pm, 
due to the Tohoku-Chihou-Taiheiyou-Oki Earthquake (previously announced 
on March 11).

At 7:15 pm on March 15, the reactor of Unit 4 achieved a cold shutdown. 
As a result, all the Units of Fukushima Daini Nuclear Power Station 
achieved the status of cold shutdown (previously announced on March 15).

As of 3:00 pm on July 8, the Units 1 to 4 remain in a cold shutdown 
(please refer to the appendix). 

< Updates are underlined >
At 2:05 pm on July 7, an employee of a partner's company found a spark 
in the breaker of power panel while a labor investigated the power panel 
in the first floor of basement of reactor building of Unit 1. At 2:30 pm 
on July 7, TEPCO workers confirmed. 
 For investigation of the causes, at around 5:37 pm on July 7, we 
 temporarily stopped residual heat removal system (B), and opened a 
 connecting breaker that supplies electricity to the breaker at 5:44 pm. 
 As a result of the investigation, we confirmed the followings. 
 (Investigation results) 
  -The power panel was located in the room where sea water flowed in and 
   was stopped, but it was being charged because the incoming circuit of 
   the power panel was connected to power supply cable of other normal 
   power panel (such as power source of residual heat removal system (B)). 
  -Discharge mark at insulating part of the cable connection conductor of 
   the incoming circuit of the power panel and salt adhesion inside of 
   the insulating cover were confirmed. 
  -The humidity in the room was high because air conditioner was stopped 
   soon after the earthquake, so that the room was not suitable condition 
   for power panel installation. 
 (Assumed cause) 
   As for the insulating part of the cable connection conductor of the 
   incoming circuit of the power panel, we didn't conduct inspection of 
   inside of the insulating cover because it was high voltage live part 
   and had risk of electrical shock. Therefore, we couldn't check the 
   salt adhesion of the connection part, and after that dew condensation 
   water occurred in the room was absorbed to it. From this, we assumed 
   that insulation resistance of the insulating part of the cable 
   connection conductor of the incoming circuit of the power panel dropped 
   and then reached spark discharge. 
 (Countermeasure) 
  -We cut off the connecting cable of the incoming circuit of the power 
   panel. 
  -Also we cut off the connecting cable of incoming circuit on similar 
   spots in the same way. 
  -We will reconfirm existence of similar spot and confirm normality by 
   thermographic inspection. 
 
After cut off of the cable, at around 9:15 pm on July 7, we restored
residual heat removal system (B). 
 
We will make our best efforts to stabilize each plant. 

Appendix: TEPCO Plant Status of Fukushima Daini Nuclear Power Station 
                                                              (PDF 16.9KB)