Both Hitachi and Toyota conglomerates are vying to get contracts to clean up the Fukushima Daiichi nuclear plant.
The contracts could bring billions to the winner, both wanting the job to replace losses because of restricted manufacturing capability.
Hitachi estimates 30 years to return the site to "green field" state, meaning within legal limits of radiation for residents.
Toshiba has estimated only ten years will be needed [Of course, if Toshiba gets the contracts, it could keep extending that time period, and the government would be loath to change horses].

Professor of Nuclear engineering at Tokyo City University, T. Matsumoto, said that decommissioning time would depend heavily on the state of the nuclear fuel. "Will it still be shaped like rods? Or will it have melted and collapsed into a big mass? You just don't know until you open up the reactor."

New York Times, International News, Sunday, April 17, 2011; "Nuclear Cleanup Plans Hinge on Unknowns.".