Workers at the crippled Fukushima Daiichi plant are concerned that hydrogen gas in the container of reactor number 1, produced by the fission process, could react violently if it comes into contact with a lot of oxygen.
"We are considering injecting nitrogen into the container of reactor number 1 because hydrogen gas has possibly accumulated in the container," a Tokyo Electric Power Co. (TEPCO) official said.
Public broadcaster NHK, citing unnamed sources, said TEPCO could start nitrogen injection at reactor No. 1 on Wednesday evening and was mulling the same procedure at reactors 2 and 3.
Experts say the risk of a hydrogen explosion could rise as the nuclear fuel rods cool and as the steam inside the containment vessel condenses into water, reducing pressure inside the unit and drawing air in through cracks.
Oxygen in the air could then react with the hydrogen to cause an explosion.
Nitrogen, an inert gas abundant in the atmosphere, would displace this oxygen.
In the days after the March 11 earthquake and tsunami crippled the plant, an accumulation of hydrogen near the reactors caused large explosions that badly damaged the outer buildings housing them.
The latest worries signal the fragility of the situation at the Fukushima Daiichi plant more than three weeks after the disasters that knocked out reactor cooling systems, triggering explosions and fires and releasing radiation.
The plant northeast of Tokyo has emitted radioactive materials into the air, contaminating farm produce and drinking water.
The concerns over hydrogen came after TEPCO reported some progress earlier in the day, announcing that leakage of highly radioactive water from a cracked concrete pit at reactor number 2 has stopped.