The melted nuclear fuel of reactors 1, 2 and 3 of the Fukushima No. 1 power plant is being slowly cooled and a cold shutdown is likely to be achieved by the end of the year as planned, disaster minister Goshi Hosono said Thursday.
The government will declare that the facility has achieved cold shutdown once it confirms the complex can maintain stability over the next several years even if it is hit by an earthquake or suffers malfunctions, he said.
In the road map for the resolution of the crisis, which is updated every month, the government and Tokyo Electric Power Co. said not only that the temperature at the bottom of the pressure vessels of all three reactors is below 100, but that the temperature inside the primary containment vessels of the reactors, where part of the melted fuel may be accumulating, was between 39 and 70 as of Wednesday.
“There have been various discussions on whether the fuel remains inside the pressure vessels, or has dropped to the (outer) primary container . . . and our explanation is that we think we are able to slowly cool the fuel including that inside the primary containers and the pressure vessels,” Hosono said at a news conference that Tepco officials also attended.
Adding to signs of further progress in restoration efforts, the amount of radioactive substances currently leaking from the crippled reactors has further declined to a maximum of 60 million becquerels per hour, or around a one 13-millionth of the level seen in the early days of the crisis, which was triggered by the devastating March 11 earthquake and tsunami.
The estimate means someone standing in the crippled plant for one year, would be exposed to up to 0.1 millisieverts of radiation, far below the government-set limit of 1 millisievert per year.
The cold shutdown is the key goal of “Step 2″ of the road map, with the government defining it as a situation in which the bottom part of a reactor pressure vessel at the plant is kept below around 100 degrees and exposure from the release of radioactive substances is significantly held down.
Hosono said the government is “cautiously” checking whether the current situation can be maintained over the medium term even if the plant experiences another earthquake, accident or malfunction.
Other tasks included in the phase have almost been completed, with workers starting to build a sunken wall between the reactors and the shore to prevent water containing radioactive substances from leaking into the Pacific Ocean.
They also finished installing a cover over reactor 1 on Oct. 28 as the building housing the unit was badly damaged by a hydrogen explosion.
After Step 2, the government and Tepco aim to start removing nuclear fuel in the spent-fuel pools of reactors 1 to 4 within two years and the melted fuel from inside reactors 1 to 3 within 10 years.