The government has revised its road map for ending the Fukushima nuclear crisis by saying it intends to achieve cold shutdown by the end of the year.
The central government and Tokyo Electric Power Co. announced the new game plan on Oct. 17.
Officials of the central government will rely on an assessment by the Nuclear and Industrial Safety Agency (NISA) as well as the opinions of outside experts to determine if cold shutdown has been reached.
In a nuclear reactor, cold shutdown refers to a state when the temperature at the bottom of the reactor pressure vessel is below 100 degrees and no new radioactive materials are being dispersed into the atmosphere.
Previously, TEPCO had envisaged achieving this goal between mid-October and mid-January.
The time frame was advanced partly because Goshi Hosono, the state minister in charge of the accident at the Fukushima No. 1 nuclear power plant, pledged at a September meeting of the International Atomic Energy Agency to achieve cold shutdown before the end of the year.
Another factor is that the reactors at the Fukushima plant are already close to reaching that stage.
As of Oct. 17, temperatures at the No. 1 to No. 3 reactors were between 70 and 90 degrees. The release of radioactive materials at the boundary to the Fukushima plant was about 100 million becquerels per hour, which is half the level of September and one-eight millionths the level immediately after the nuclear accident triggered by the March 11 Great East Japan Earthquake.
The maximum radiation exposure level over the course of a year has also fallen to 0.2 millisievert, which is under the 1 millisievert standard set by the central government.
TEPCO officials said the dispersal of radioactive materials had fallen by half because the reactor temperatures had fallen over the past month.
Yasuhiro Sonoda, a parliamentary secretary at the Cabinet Office, said: "We will determine if the figures are appropriate and also if TEPCO can maintain a cold shutdown state (in the weeks ahead). Only then will we be able to say that we have achieved cold shutdown."
Now that the reactors have been stabilized, NISA officials will try to assess if this situation can be maintained.
Experts will be asked for their opinions at a meeting set to be held in Iwaki, Fukushima Prefecture, on Oct. 22.
These two factors will figure largely in deciding if cold shutdown has been achieved.
TEPCO also announced that it intends to maintain cold shutdown over the next three years ahead of beginning work to decommission the Fukushima reactors.
TEPCO said it now had the means to prevent a recurrence of another accident. Unlike in March, and in the months that followed, it said it now had the equipment to properly cool the reactors should major aftershocks shake the area.
Officials also said new equipment to pump water into the reactors will be installed in mid-November. They said the measure would further heighten safety.