Kan's statement was the first government acknowledgment of how long the cleanup process is likely to be, the Russian news agency RIA Novosti reported.
Tokyo Electric Power, which owns the reactors hit by the March 11 earthquake, said removing the melted nuclear fuel will only begin in 2021, NHK, the Japanese public broadcasting company, said.
The Japan Industrial Atomic Forum reported almost two-thirds of the country's 54 nuclear reactors are out of service, the highest ratio since 1979, Japan Today said. That was when many reactors suspended operations following the near-meltdown at Three Mile Island in Pennsylvania.
As of the end of June, 35 reactors were not operating. In an editorial, Yomiuri Shimbun said every nuclear plant in the country could suspend operations by the end of the year, something the newspaper called "an alarming prospect."