(CNN) -- Engineers may be able to complete the shutdown of damaged reactors at Japan's Fukushima Daiichi nuclear power plant ahead of schedule, the plant's owner reported Monday.
The Tokyo Electric Power Company's plan for winding down the crisis caused by the historic March 11 earthquake and tsunami had called for completing the shutdown process by January. But in a six-month update to its April "road map," the utility said the reactors could reach their "cold shutdown" points by the end of the year.
Temperatures in the three reactors where meltdowns occurred in the wake of the disaster have already been brought down below 100 degrees Celsius (212 F), but the company has to maintain those conditions for some time before declaring the reactors in cold shutdown, Tokyo Electric spokesman Yoshikazu Nagai said.
"We have to keep this situation continuously. We have to see if it is stable or not," Nagai said.
In addition, decontamination systems have sharply cut down the amount of radioactive water that had been piling up in the reactors' turbine plants while workers pumped hundreds of tons of fresh water into the damaged reactors every day. Nagai said 128,000 tons of contaminated water has been treated, leaving about 43,000 tons remaining -- well above the 100,000 tons estimated to have collected earlier this year. The treated water is now being recirculated through the reactors to keep them cool, he said.
And Tokyo Electric has cut ongoing radioactive emissions from the plant to about half of their recent levels, or about 6% of what a typical resident of an industrialized country receives in a year. The number is about one eight-millionth of the amount released in the days following the tsunami, which swamped the plant on the Pacific coast of northern Japan and triggered meltdowns in three of the plant's four operating reactors.
But experts have said it will take years -- perhaps decades -- to fully clean up the worst nuclear disaster since Chernobyl. Hydrogen explosions blew apart the No. 1 and No. 3 reactor housings, while another hydrogen blast is suspected to have damaged the No. 2 reactor and fires believed caused by heat from the No. 4 spent fuel pool damaged that unit's reactor building.
Plant workers have nearly completed a new reactor housing to cover the damaged No. 1 reactor building, while they are still trying to clear away rubble surrounding units 3 and 4 before starting construction on similar structures, Nagai said. Workers have re-entered all four reactor buildings since the spring, but parts of the buildings remain inaccessible because of high radiation levels and debris, he said.
The plume of radioactive particles that spewed from Fukushima Daiichi 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, but lifted evacuation standby notices for other nearby towns in late September.
A Friday report by an International Atomic Energy Agency team that recently visited Japan praised the country's efforts to decontaminate the area, but urged Japanese authorities "to avoid over-conservatism" in the effort. Japan's main strategy has been to scrape off the top 5 centimeters (2 inches) of topsoil from contaminated areas -- a plan the IAEA found could produce "huge amounts of residual materials" -- but it is conducting a variety of tests in different areas, the report concluded.