Work to remove melted fuel from the three crippled reactors at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear plant could start in 2020, the government and Tepco optimistically said Thursday, based on a revised, albeit vague, plan to decommission the stricken complex, a process expected to take decades.

The original melted-fuel extraction was expected to start in 2021, but the government, without elaborating, believes an improvement in work efficiency can move the date forward.

Tepco, however, said an exact start date currently is hard to forecast because the position and state of the fuel in reactors 1, 2 and 3, which suffered core meltdowns, remains unclear and all the utility can do at present is try, with makeshift equipment, to keep water circulating through the damaged containment vessels to prevent further massive radioactive fallout.

The moved-up fuel extraction timetable is the first major revision of the road map outlining the 40-year-long process of scrapping reactors 1 to 4 at the six-reactor complex. The original schedule was released in December 2011, after Fukushima No. 1, ravaged by the March 11, 2011, Great East Japan Earthquake and monster tsunami was deemed in a stable state of “cold shutdown.”

The plant is technically currently in the first phase of decommissioning, with Tepco hoping to start in November extracting the fuel inside the spent-fuel pool located outside but atop reactor 4, whose building was ripped apart in a hydrogen explosion.

Reactor 4 was offline for maintenance, and thus empty of fuel, when the catastrophe struck, so only its spent-fuel pool needs to be unloaded, although due to the high levels of radiation in and around the building, this will be a delicate operation requiring high levels of technology. Finding a safe location to store the extracted fuel will also pose hurdles.

The second phase of the decommissioning, based on the revised plan, will entail the removal of the melted fuel from crippled reactors 1 and 2 starting in fiscal 2020 if possible, followed by work to start removing the melted fuel inside reactor 3 in the latter half of fiscal 2021 at the earliest. Reactor 3’s fuel is the highly lethal mixed uranium-plutonium oxide (MOX) fuel.

The extractions may be delayed if proper equipment isn’t available to deal with the three stricken reactors, whose levels of damage and radiation differ.

The buildings housing reactors 1, 3 and 4 were damaged by hydrogen explosions, while the radiation level inside the reactor 2 building is very high.

Another scenario points to starting the fuel removal of reactor 1 in fiscal 2022, that of reactor 2 in fiscal 2024 and reactor 3’s fuel in fiscal 2023.

The original road map only suggested the fuel removal may start in December 2021, without specifying which reactor would be worked on first.

The fuel inside reactors 1, 2 and 3 is believed to have melted through the pressure vessels and accumulated somewhere in the outer primary containers, making the task of extraction more challenging than in the case of the 1979 Three Mile Island accident in Pennsylvania.