Article from NHK News :
" The operator of the Fukushima nuclear power facility plans to cool the reactors by filling their vessels with water. However, that process may be hampered by wastewater contaminated with highly radioactive materials.
According Tokyo Electric Power Company's blueprint for bringing the troubled facility under control, the Number 1 and 3 reactor vessels will be filled with water up to the height of the nuclear fuel rods by the middle of July. This is aimed at cooling the reactors in a stable manner.
TEPCO says that the water level has begun rising in the Number 1 reactor. It says water injected to cool the reactor vaporizes out of the reactor and then turns into water after being cooled inside the container.
However, if the container has been damaged, then highly radioactive water may seep out.
The utility needs to check the reactor turbine building for any water leakage from the building housing the reactor, but workers cannot enter the reactor building at present. However, the effort to identify the source of a leak is difficult because of radioactive water inside the basement of the turbine building.
Work to move contaminated water from the Number 2 reactor is already underway. However, it's not clear when they can begin moving contaminated water from the Number 1 reactor."