On May 11, 2011, a worker, who was working on blockage of a vertical shaft 
near the water intake of Unit 3, found water flowing into a pit (a vertical 
shaft made of concrete) through the duct where electric wires were installed.
As a result of our investigation of the potential leakage of radioactive 
water off the site, the outflow of the water from the pit to sea was 
confirmed on May 11.
Thereafter we inserted fabrics to the duct leading to the pit and filled 
concrete inside the pit. We confirmed that the outflow was stopped on May 11.
                                     (Previously announced on May 11, 2011)

On May 11 we received following verbal instructions from Nuclear and 
Industrial Safety Agency (NISA) of Ministry of Economy, Trade and Industry;
• to check whether there is any impact on the ocean, 
• to take measures immediately to stop the leakage, and
• to identify the inflow/outflow routes and their condition urgently and 
  report them.

Then we compiled preventive measures and countermeasures to prevent the 
water from spreading to the outside of port, in addition to the condition 
of inflow/outflow routes and the impact on the ocean as instructed. On May 
20, we reported them to NISA.
                                     (Previously announced on May 21, 2011)

On May 23, we received an instruction document from NISA "Regarding the 
countermeasure against water outflow including radioactive materials to 
the outside from Unit 3 of Fukushima Daiichi Nuclear Power Station 
(instruction)."
                                     (Previously announced on May 24, 2011)

Based on the instruction document, we investigated conditions of vertical 
shafts and shore protections that we had not finished confirming and made 
plans for countermeasures to prevent outflows. On June 1 we put them 
together and reported to NISA.
                                     (Previously announced on June 2, 2011)

Based on the instruction document, we investigated the status of 
accumulated water inside the facility. On June 2 we put them together and 
reported the storage and disposal plan for contaminated water to NISA. 

Appendix: Plan to prevent water leakage containing highly concentrated 
radioactive materials to outside environment in Fukushima Daiichi nuclear
power plant (summary)(PDF 157KB)

* Regarding the countermeasure against water outflow including radioactive 
  materials to the outside from Unit 3 of Fukushima Daiichi Nuclear Power 
  Station (instruction)
                                                [May 23rd, 2011 NISA No.2]

On May 20th, 2011, NISA received a countermeasure report from TEPCO against 
water including radioactive materials (hereafter called "contaminated 
water") to the outside from around the intake canal of Unit3 of Fukushima 
Daiichi Nuclear Power Station.
On the report, as countermeasures to prevention of recurrence, obstructing 
the shaft, installing some sandbags inside the intake canal, implementing 
circulating purification system, etc. will be implemented.
Nuclear and Industrial Safety Agency (hereafter called "NISA"), in addition 
to countermeasures TEPCO reported, would like TEPCO to implement following 
actions by each due date in order to enhance countermeasures against 
prevention of recurrence of contaminated water outflow at the site.

1. On TEPCO's report, although 27 points of vertical shafts, which lead to 
   seawater piping trench will be obstructed using concrete etc by the end 
   of June, 2011, we would like TEPCO to investigate the status of vertical 
   shafts and seawalls (cracks of quay etc.), which has not been confirmed 
   the status yet. For such points that TEPCO cannot deny the possibility 
   of water outflow, TEPCO should take countermeasures to prevent water 
   outflows and report to NISA by June 1st, 2011.

2. On TEPCO's report, continuous monitoring of seawater inside/outside of 
   port at the site and enhancing monitoring system as same as Unit 2 for 
   analyzing seawater inside of the silt fences at Unit 1, Unit 3 and Unit 
   4 will be implemented. However, we would like TEPCO, in addition to the 
   above mentioned measures, if TEPCO confirms significant increase in 
   density of radioactive materials based on the result of monitoring 
   inside the port, TEPCO should immediately conduct visual investigation 
   etc around the port and if some water outflows are confirmed, TEPCO 
   should implement proper measures to stop the water outflows. Also, the 
   results must be reported to NISA.

3. Accumulated contaminated water should be property reduced and to 
   decrease the possibility of occurrence of water outflow, TEPCO should 
   conduct investigation to a maximum extent regarding the status of 
   accumulated water inside the   facility. The storage and disposal plan 
   for contaminated water must be reported to NISA by June 1st, 2011.