Japan's Prime Minister said Friday that a "cold shutdown" has been achieved at the Fukushima Daiichi nuclear power plant, a symbolic milestone that means the plant's crippled reactors have stayed at temperatures below the boiling point for some time. The announcement is a turning point in the crisis but experts say it will take years -- perhaps decades -- to fully clean up the worst nuclear disaster since Chernobyl. The plume of radioactive particles that spewed from Fukushima Daiichi -- where reactor cooling systems failed in the aftermath of Japan's devastating earthquake and tsunami in March -- displaced about 80,000 people who lived within a 20-kilometer (12.5-mile) radius of the plant, as well as residents of one village as far as 40 kilometers to the northwest. The government has yet to determine when those evacuated can return to their homes.