The government and Tokyo Electric Power Co. said Tuesday they have successfully achieved consistent and stable cooling of the reactors at the Fukushima No. 1 plant and will by mid-January reduce the amount of radioactive materials being released.
They also said some evacuated residents may be able to return home after “Step 2” is completed.
With “Step 1” — stable cooling of the reactors — complete, Tepco said it will now try to bring them into a state of cold shutdown.
Disclosing an updated road map to get the stricken plant back under control, Goshi Hosono, state minister in charge of the crisis, said the second phase will take three to six months.
While working on stabilizing the plant, the government will make utmost decontamination efforts so people will be able to return to their homes, Hosono said.
“It will depend on radiation levels in the various areas, but I think we can achieve some specific results even for the evacuation area (within 20 km of the plant),” he said.
On efforts to cool the reactors, the new road map defines cold shutdown as bringing the temperature at the bottom of the pressure vessels to below 100 degrees, while largely reducing and controlling the leakage of radioactive materials.
Cold shutdown usually means the temperature of the reactor-core coolants has been brought below 100 degrees, but this has been redefined for the Fukushima crisis because the cores in reactors 1 through 3 are believed to have melted down to the bottom of their pressure vessels.
Tepco said it will keep cooling the reactors through the current circulated cooling system in which the highly radioactive water leaking from the reactors is processed by a water treatment system and then pumped back into the reactors.
But the system is not perfect, as it has experienced numerous problems and has been halted several times. Ultimately, the leakage of contaminated water won’t stop unless cracks or holes in the containment vessels are plugged.
Other goals for the second phase include continuing to process the radioactive water, safely storing radioactive waste created through the water treatment system, setting up a cover for the reactor 1 building and further improving the environment for workers at the site.
For the first time, Tepco said it will take about three years to move through the medium-term range of the crisis, which includes getting the fuel rods out of the spent fuel pools and constructing a full-scale water treatment facility at the site.
The government and utility also said the amount of radioactive materials currently released from crippled reactors 1, 2 and 3 is estimated at about 1 billion becquerels per hour at most. According to them, the surrounding area’s radiation level would be a maximum 1.7 millisieverts per year in this case.
On March 15, the amount was estimated at 2 quadrillion becquerels per hour, Tepco said.
Tepco disclosed the first version of the road map on April 17 and said the first phase would take three months.
The government and Tepco stressed that the goals of the initial phase have been basically achieved.
For instance, one of the goals was to cool the reactors through a circulation cooling system, and the injection of nitrogen gas into reactors 1 through 3 to prevent another hydrogen explosion has been achieved as well.