A semi-governmental organization has come up with three possible methods to tackle the most difficult and dangerous task at the stricken Fukushima No. 1 nuclear plant: removing the melted nuclear fuel from the reactors.
A semi-governmental organization has come up with three possible methods to tackle the most difficult and dangerous task at the stricken Fukushima No. 1 nuclear plant: removing the melted nuclear fuel from the reactors.
All three methods proposed by Nuclear Damage Compensation and Decommissioning Facilitation Corp. (NDF) on April 9 carry the risk of radiation leaks and exposure to workers.
The difficulty in implementing these methods is also compounded by the fact that high radiation levels have prevented workers from determining the precise location and shape of the melted fuel.
The NDF, which is providing technological advice on removing the melted fuel from the No. 1, No. 2 and No. 3 reactors of the Fukushima plant, will incorporate the three methods in a road map scheduled to be revised by the government and the plant’s operator, Tokyo Electric Power Co., in spring.
The preferred method, and the only one considered so far, would involve pumping in water to fill the reactor containment vessels to the upper part. The melted nuclear fuel would then be removed from above, and the water would keep radiation exposure of the workers at low levels, according to the plan.
But this “water-covered method” will not work if the containment vessels are corroded or cracked. In addition, if the containment vessels are filled with water, their quake-resistance capabilities would weaken.
“The water-covered method is desirable from the viewpoint of safety,” said Hajimu Yamana, the NDF vice president who is in charge of the division supporting decommissioning work. “But it is not certain whether we can completely prevent water leakages from the containment vessels.”
For that reason, the NDF also proposed two “airborne methods,” under which water would fill only the bottom part of the containment vessels and the melted fuel would be removed through the air.
In one of these airborne methods, the melted fuel would be taken out from the upper part of the containment vessels. In the other method, the fuel would be removed from a hole drilled into the side of the containment vessel.
The big challenge in the two airborne methods is preventing radioactive materials from being scattered in the air and contaminating the workers.
“Respecting the experts’ opinions, we want to tackle the revision (of the road map),” said Yosuke Takagi, senior vice minister of economy, trade and industry.
The NDF is also tasked with disposing of radioactive waste and assisting in compensation payments to residents affected by the nuclear accident caused by the March 2011 Great East Japan Earthquake and tsunami.
The NDF explained the three possible methods to residents at a meeting in Koriyama, Fukushima Prefecture.