Tokyo Electric Power Company, the embattled operator of the plant, said it hopes to bring the damaged reactors at the six-unit Fukushima nuclear power station to a stable condition known as a "cold shutdown" in about six to nine months.
It said the stable cooling to the reactors and spent fuel pools is expected to be restored in about three months.
Announcing TEPCO's phased roadmap "for the moment" for bringing the complex in Fukushima prefecture under control, the utility's Chairman Tsunehisa Katsumata offered apology for the ongoing nuclear crisis triggered by the March 11 magnitude-9 quake and tsunami that have left nearly 30,000 people dead or unaccounted for in Japan's northeast.
TEPCO said it needs three months to achieve "steady reduction" in radiation and an additional three to six months to control radioactive emissions and curb radiation substantially.
It said it is addressing the immediate challenges of preventing hydrogen explosions at the Nos. 1 to 3 reactors of the plant and emission of water contaminated with high-level radiation from the No. 2 reactor.
To show solidarity with Japan, US Secretary of State Clinton arrived in Tokyo on a five-and-a-half-hour visit on the final leg of a global tour that previously took her to Berlin for NATO talks on Libya and Seoul to tackle the North Korean nuclear issue.
During her visit, Japan and the US affirmed their partnership in efforts to rebuild the tsunami-ravaged nation, with the involvement of governments and private sectors of the two countries.
Clinton had tea with Emperor Akhito at the Imperial Palace after the monarch extended her a rare invitation, which is usually done in the the case of the head of a state.
She also held talks with Prime Minister Naoto Kan and her Japanese counterpart Takeaki Matsumoto.
The US is confident that Japan would recover and act as a very strong economic and global player for years to come, Clinton told Kan, who thanked her for the US help.
Clinton, who addressed a joint press conference with Matsumoto, pledged unwavering support for Japan in the process of rebuilding of the nation, while her Japanese counterpart vowed that Tokyo will "fully disclose" information on its battle to contain the emergency at the Fukushima nuclear plant.