TOKYO - The crippled reactors at Japan’s tsunami-hit nuclear power plant have reached stability more than four months since the disaster, and the plant is on track for a cold shutdown within six months, the government and plant operator said yesterday.

Workers have toiled in hot and harsh conditions to stabilize the Fukushima Daiichi plant since the March 11 earthquake and tsunami destroyed reactor cooling systems, triggering partial meltdowns of the reactors and making the disaster the world’s worst nuclear crisis since Chernobyl.

The assessment of reactor stability was based on several milestones: Temperatures at the bottom of reactor pressure vessels are no longer climbing, a makeshift system to process contaminated water works properly after initial problems, and nitrogen injections are helping prevent more explosions.

Radiation around the plant has shown a “sufficient decrease’’ from peak levels measured soon after the disaster.

The progress achieves the Tokyo Electric Power Company’s initial goals of its road map to bring the plant under control, according to the report released by the government and the company, also known as TEPCO.

“The accident has not been resolved, but we have been making progress steadily,’’ said Japan’s trade and industry minister, Banri Kaieda. “We will continue our utmost effort so that we can bring this to an end as soon as possible.’’

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