The Fukushima Daiichi plant, 240 km (150 miles) northeast of Tokyo, was wrecked by the March 11 earthquake and tsunami, which knocked out reactor cooling systems, causing meltdowns of nuclear fuel rods. A cold shutdown is when water used to cool nuclear fuel rods remains below its boiling point, preventing the fuel from reheating. Prime Minister Yoshihiko Noda may declare a cold shutdown because a Nov. 30 analysis by plant operator Tokyo Electric Power Co showed that temperatures for the nuclear fuel lying at the bottom of the containment vessel have stabilised, the paper said. Radiation levels at the reactors have also fallen significantly, it said. Declaring a cold shutdown will have repercussions well beyond the plant as it is one of the criteria the government has said must be met before it begins allowing 80,000 residents evacuated from within a 20 km (12 mile) radius of the plant to return home. But even if a cold shutdown is declared, Tokyo Electric has acknowledged before that it may be unable to remove the fuel from the reactors for another 10 years, and experts say the cleanup at the plant could take several decades.