Tepco began preparatory work on Wednesday to dismantle the cover on the reactor 1 building at the crippled Fukushima No. 1 nuclear plant, as a step toward eventually removing the melted fuel inside.

The cover was installed to contain radioactive materials after the building was heavily damaged by a hydrogen explosion soon after the nuclear disaster began in March 2011.

Tokyo Electric Power Co. plans to finish removing the cover around March 2016. It will then clean up the debris from the hydrogen explosion.

Tepco said removing the melted fuel inside the crippled reactor will begin in 2020 at the earliest, though it still doesn't have a precise picture of the situation inside the reactor, which is needed in order to devise a detailed plan for the extraction.

On Wednesday morning, Tepco started making holes in the roof of the building cover to insert anti-dispersal agents to prevent radioactive dust from being scattered. The actual dismantling won't start until March, the utility said.

Tepco had initially sought to begin preparations to dismantle the cover by March 2014, but the plan was delayed due to equipment failure.

The start was delayed again after local residents voiced concern that debris cleanup work at the plant may have scattered radioactive particles that contaminated rice paddies in nearby areas.