According to Tokyo Electric Power Company (Tepco), the workers were on duty air ventilation system installed in a single reactor to filter radioactive particles that come out of the reactors.
Reactor one was severely damaged by the blast which hit the nuclear facilities. Tepco said the 12 workers will work alternately for 10 minutes.
All workers wear safety clothing and carrying oxygen cylinders.
March earthquake damage in the reactor cooling system so that triggering a radiation warning.
The Japanese government has decided the area within a radius of 20km from the Fukushima nuclear power plant that exploded into the area that should not be accessible.
It is estimated that nearly 14 thousand people were killed by the earthquake and tsunami that menghempas Japan last March, and more than 13 thousand people listed as missing.
The value of material losses due to this disaster is estimated to reach $ 300 billion, making it the costliest disaster in the world