An entry point for some of the groundwater flooding the crippled Fukushima No. 1 plant has been found at reactor 1, according to Tokyo Electric Power Co.
Tepco will consider measures to halt or divert the water by conducting more surveys to determine exactly where it is entering. Cracks in the basement are considered a possibility.
An estimated 400 tons of toxic groundwater are flowing into the four damaged reactor units each day, compounding the volume of highly radioactive water being produced by the makeshift cooling apparatus set up after the triple core meltdowns of March 2011. The fuel inside must be submerged at all times to prevent it from igniting.
The groundwater is believed to be the primary source of the radioactive material entering the sea and potentially poses great danger to the environment.
The entry point is near a basement wall of unit 1's turbine building, which is connected to and on the east side of the reactor building. Tepco workers found the entry point by drilling a hole into the ceiling of the basement and inserting a video camera, which captured images of water trickling from a point above the wall.
The water used to cool the fuel eventually flows into the turbine building, where it is believed to mingle with water intruding from outside.
The turbine building is also connected to an underground trench that runs toward the coast. Highly radioactive water from the trench is believed to be mixing with separate groundwater flows before entering the sea.
Reactors 1, 2, 3 and 4 and their turbine buildings have similar layouts. Stopping the invasion of the groundwater is thus considered vital to reducing the overall volume of contaminated water.
Tepco has been constructing hundreds of storage tanks to contain, filter and recycle the tainted water, but some have sprung large leaks.