1 Novembre 2014
October 31, 2014
The government and Tokyo Electric Power Co. (TEPCO) announced on Oct. 30 that removal of melted fuel from the No. 1 reactor at the disaster-hit Fukushima No. 1 Nuclear Power Plant would be delayed by five years, until fiscal 2025.
They also announced that work to remove spent fuel from a cooling pool will not begin until fiscal 2019, two years later than originally planned. The delays are the result of the removal of debris and the installation of cranes taking longer than expected.
The announcement marks the first delays in the decommissioning schedule. TEPCO said, however, that the move would not result in an overall delay to the decommissioning process, which is expected to take 30 to 40 years.
The No. 1 reactor houses 392 fuel rods in its cooling pool, while melted fuel remains in the nuclear pressure vessel and reactor containment vessel. In a meeting on Oct. 30, the government and TEPCO decided to adopt a two-step process with separate measures to remove fuel from the cooling pool and melted fuel. First, a cover will be installed on the top floor of the reactor building. After a special crane for the fuel pool removes fuel, then workers will use a container and crane setup to remove melted fuel. The government and TEPCO say that they chose this method because there are many unknown factors in the removal of melted nuclear fuel, and because they hope to remove the fuel from the cooling pool at an early stage.
At the No. 1 reactor, preparations began this month to remove a cover designed to prevent the spread of radioactive materials, so that debris could be removed from the top floor. This process itself was delayed by six months. Because of this, and the fact that the two-step process is laborious, it is believed the government and TEPCO decided to delay the start of fuel removal work.
At the No. 2 reactor, meanwhile, since radiation levels are high and decontamination of the reactor building is difficult, officials have decided to reconsider the method of removing nuclear fuel. Officials are set to decide on a method in fiscal 2016, but there is a high possibility that removal work will fall behind schedule.
In August, work at the No. 3 reactor was suspended after a large piece of debris fell into the cooling pool while debris was being removed from around the pool's edge. Officials plan to remove fuel from the pool next fiscal year, but the outlook for this work is unclear.
It is expected that work to remove fuel from the No. 4 reactor pool will be completed this year.
The decommissioning schedule was established under the Democratic Party of Japan-led administration in December 2011. It was revised in June last year, accelerating the removal of melted fuel by up to a year and a half.
The disaster at the Fukushima No. 1 plant, triggered by the March 2011 Great East Japan Earthquake and tsunami, resulted in core meltdowns at reactor Nos. 1-3. Nuclear fuel has passed through the reactor pressure vessels, and caused damage to the containment vessels. The government and TEPCO plan to fill the containment vessels with water and remove about 450 metric tons of melted fuel. But it remains unknown where the melted fuel actually lies. Furthermore, officials have located only two damaged areas in the containment vessels of the three reactors.
In the Three Mile Island meltdown in the United States, it took six years before the removal of melted fuel was begun, though the pressure vessel was not damaged. Fukushima presents conditions that are far more difficult, and it is unclear when the work can be completed.
October 31, 2014(Mainichi Japan)