Photo/Illutration A document released by the Nuclear Damage Compensation and Decommissioning Facilitation Corp. carries schematic diagrams of the total submersion method and other proposals. (Keitaro Fukuchi)

IWAKI, Fukushima Prefecture--A government-authorized corporation said it is considering submerging the No. 3 reactor building at the Fukushima No. 1 nuclear power plant to retrieve melted nuclear fuel debris from the reactor.

The Nuclear Damage Compensation and Decommissioning Facilitation Corp. (NDF) said Sept. 3 that the entire reactor building would be enveloped in a steel structure before being engulfed in water, according to the proposal.

“No radioactive materials would be swirling up underwater, so there would be almost zero impact on the outside,” NDF President Hajimu Yamana said.

High radiation levels in the reactor building deny safe human access.

The total submersion method, which has no precedent, would help reduce workers' exposure to radiation as water provides an effective shield against it.

NDF officials said they will study other methods as well before proceeding to narrow down feasible options.

The NDF proposal for submerging the entire reactor building was presented at a government meeting held in Iwaki, Fukushima Prefecture.

Yamana said the NDF will study the feasibility of the work being proposed and consider the alternative option of retrieving fuel debris from the top or the side of the containment vessel without filling the vessel with water.

“I cannot say anything for sure yet (about the feasibility of the total submersion method),” Yamana told The Asahi Shimbun following the meeting. “We are still in the very, very early stages of concept study. There are still a lot of things to study as the attempt would be the first of its kind in the world.”

A separate option of filling with water the containment vessel housed in the reactor building was previously considered for the fuel debris retrieval process, but the proposal was shelved after it was found it would be difficult to fill the holes in the containment vessel.

An estimated total of 880 tons of fuel debris is left inside the No. 1, No. 2 and No. 3 reactors at the Fukushima No. 1 nuclear plant. Finding a way to retrieve the debris represents the biggest hurdle to decommissioning the hobbled plant.

Plant operator Tokyo Electric Power Co. initially had plans to begin retrieving fuel debris from the No. 2 reactor on a trial basis before the end of last year.

The utility, however, has put off the prospective start date to the second half of fiscal 2023 due partly to delays in equipment development.

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