Three methods proposed for removing melted fuel from Fukushima No. 1 reactors — The Japan Times; The Yomiuri Shimbun

” FUKUSHIMA – The Nuclear Damage Compensation and Decommissioning Facilitation Corp. on Thursday proposed three methods for retrieving highly radioactive nuclear fuel debris in three crippled reactors at Tokyo Electric Power Co.’s disaster-stricken Fukushima No. 1 nuclear power plant.

The proposals, presented at a meeting of officials from Tepco, the central government and municipalities in Fukushima Prefecture, will be reflected in a decommissioning road map that the government and Tepco are set to release around May.

The three reactors underwent core meltdowns in March 2011, leaving melted nuclear fuel debris on the floor of their containment vessels. The decommissioning aid body hopes to establish concrete procedures by the first half of fiscal 2018.

One of the three proposed methods removes the debris in a submerged condition, with a containment vessel filled with water to shield against radiation and prevent the spread of radioactive materials during the retrieval process.

An alternative dry method carries out the retrieval in a partially submerged condition, with water used only when the debris is cut loose from the vessel floor. The debris would be removed from either the top, under one plan, or the side of the vessel, under another.

The submersion method requires the reactor damage to be accurately identified and repaired before water is poured in. The dry method, on the other hand, requires continuous cooling of the retrieved debris and measures to prevent radioactive materials from scattering.

Radiation levels at the three reactors are so high that workers have been unable to approach their containment vessels or identify the location of the debris. All the three methods call for an assessment beforehand of radiation contamination as well as decontamination procedures.

Tepco plans to begin inspections of reactor 1 Friday using robots mounted with cameras and radiation-measuring equipment. ”

source

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Read a related article by The Yomiuri Shimbun

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