Photo/IllutrationThe Asahi Shimbun

An organization looking into the decommissioning of the Fukushima No. 1 nuclear power plant proposed removing nuclear fuel debris without first submerging the material in water to prevent the spread of radioactive dust.

The Nuclear Damage Compensation and Decommissioning Facilitation Corp. (NDF) presented its proposal at a gathering held July 31 in Iwaki, Fukushima Prefecture, which was sponsored by the Ministry of Economy, Trade and Industry.

The so-called "water-covered method" for removing the fuel debris from the stricken reactors was considered soon after the March 2011 disaster at the Fukushima plant. However, major issues that would have to be resolved included repairing the containment vessels that were damaged by the hydrogen explosions following the meltdowns in the reactors. Leaks would have to be repaired before water could cover the nuclear fuel debris.

NDF officials have concluded that it would be difficult to repair the various holes in the containment vessel to make it sturdy enough to withstand the water pressure.

There were also concerns that handling the nuclear fuel debris in water could lead to the possibility of the material once again reaching a state of criticality.

Instead of a water-covered method, the NDF is leaning toward an "airborne method" in which air pressure within the containment vessel would be lowered to restrain the spewing of radioactive dust.

The nuclear fuel debris remaining in the pressure vessel would be removed using a remote-controlled robot arm. The debris in the containment vessel would be removed using the robots from entry points drilled into the side of the vessel.

The debris would be placed in specialized containers and stored within the grounds of the Fukushima plant.

Based on the new debris removal proposal, Yosuke Takagi, senior vice minister of economy, trade and industry, instructed ministry officials to begin work on revising the road map for decommissioning the Fukushima No. 1 plant reactors.

The central government and Tokyo Electric Power Co. are planning to release the new road map in September. Under the current schedule, the specific debris removal procedure will be decided on within fiscal 2018. Actual removal of the debris will begin at one of the three reactors from 2021.