On the 2nd floor of the reactor building (controlled area) of the unit 7, 
a shift operator during a plant walk-down found water ooze and a water 
puddle at around 5:21pm on Oct.20th. There was a microscopic crack (width: 
about 0.1mm, length: about 3.5m) on the joint of the 2m-thick reinforced 
concrete wall near the elevator. 
Water from the puddle had been sampled and analyzed immediately. Although 
no radioactive material was found, because a minute amount of water 
continued to ooze, we covered the area to prevent water from spreading and 
continued monitoring the crack.

Today, at 6:00am, we took samples of the water again and detected some 
radioactive materials (cobalt-60 and cesium-137) at around 10:27am. 

The total amount of water leakage from yesterday amounted to about 6.5 
liters with a radioactivity of 250Bq, which is equivalent to that of 
30cm3 of radon spa. The water has been wiped off. 

No abnormality has been found as for the water level of the spent fuel 
pool and the level gauge of pipes connected to the pool liner. Since a 
minute amount of leakage is continuing, we will keep observing and conduct 
the research of the cause.

The leakage is contained within the controlled area and hence there is no 
radioactive impact to the atmosphere. Furthermore, this incident does not 
pose any safety issues to the plant since the relevant concrete wall does 
not require air- or water-tightness and since the crack is a minor one 
that does not affect the structural integrity of the building.