Naohiro Masuda, head of decommissioning for the damaged Fukushima
On March 2, 2016, five years after the meltdown caused by the 2011 earthquake and tsunami, Naohiro Masuda the Chief Decommissioning Officer of the Fukushima nuclear plant said that operators have yet to locate where the melted nuclear fuel has gone: “There are melted fuels in units 1, 2 and 3,” Masuda said. “Frankly, we do not really know what the situation is for these (melted fuel), nor where it has gone.”
One year later the melted fuel has not yet been located with certainty. The two major problems are first to find where it is, and if found how to remove it from where it is. Both jobs rendered extremely difficult by high levels radiation frying the robots’ electronic semiconductors….
How will melted fuel at Fukushima plant be removed?
The Mainichi answers common questions readers may have about how disaster-response workers plan to remove melted fuel from the disaster-stricken Fukushima No. 1 Nuclear Power Plant.
Question: What methods are being considered for removing the fuel?
Answer: Innovation will be needed in order to avoid exposing people to radiation, due to the high levels of radiation released from the fuel. One method under consideration is to fill the containment vessels holding the fuel with water, since water has radiation-blocking properties.
Q: Aren’t the containment vessels ruptured?
A: Just like you can’t fill a cup with water if it has a hole in it, the water-filling method won’t work if the containment vessels are ruptured. If they are, then another possible method is removing the fuel from the air.
Q: Which way is better?
A: Both have advantages and disadvantages. The water method could require finding and patching holes in the containment vessels. The air method wouldn’t need this, but could cause dust and other particles containing radiation to be released. The national government and plant owner Tokyo Electric Power Co. (TEPCO) will discuss as early as this summer about these two plans.
Q: What is the fuel like now?
A: At the time of the meltdown, the reactors at the plant were heated to over 2,000 degrees Celsius. The melted fuel is thought to have mixed with equipment in the plant, concrete and other materials, and to have cooled to a rock-like state. It will have to be cut out and removed.
Q: How will the fuel be cut loose?
A: The plan is to use a remotely-controlled robot. However, high-tech electronics using semiconductors are easily broken by radiation. There are ideas to make the robot use hydraulics or springs for its movement, to make it resistant to the radiation. Robot technology will be the key to a successful decommissioning of the reactors.
(Answers by Mirai Nagira, Science & Environment News Department)