Original article from NHK World News – Looking Inside Fukushima Daiichi, August 20, 2014, by Kenichiro Okamoto.
Workers have begun the difficult task of decommissioning the Fukushima Daiichi Nuclear Power Plant. One of the biggest hurdles they’re facing is how to remove melted fuel from the crippled reactors.
First they need to know the condition of the fuel. Experts believe it has cooled down and turned into debris. But engineers with Tokyo Electric Power Company have not been able to check the actual state of the debris due to high levels of radiation. Now, they might have figured out a way to measure the highly toxic materials.
Elementary particles called muons rain down from space. Every minute,ten-thousand muons per square meter reach earth. Scientists rely on this particle to probe materials that are beyond our reach. One example is volcanic magma. The technique is called muon imaging, or Muon Tomography. When the particles hit a high-density object, such as magma, they lose energy or are absorbed. By measuring these changes, scientists can determine the shape of the magma in a way that resembles an X-ray. Researchers are now hoping to use this technique to gain a better understanding of the situation inside the damaged reactors at Fukushima Daiichi.
“By using muons, we expect to be able to look for the presence of heavy materials, even if radiation levels are so high that we cannot approach the area,” says Hirofumi Fujii of the High Energy Accelerator Research Organization. One of the studies is being conducted by scientists from Toshiba and the US Los Alamos National Laboratory. Their plan is to place detectors on opposite sides of the reactor. The detectors will be used to track the behavior of muons as they pass through the concrete walls and the shielding of the reactor, in a bid to determine the status of the molten fuel.
The longer the measurements take place, the more accurate the resulting image becomes. Tests are now underway to develop the equipment needed at Fukushima Daiichi.
Kenichiro Okamoto has been covering the story. He explains what lies ahead for the scientists.
Team members face a number of major challenges. The first is installing the equipment. The detectors are very large and heavy. The molten fuel inside the reactors is believed to have sunk to the bottom of the containment vessels. So scientists must place the detectors around the vessels…deep underground. The job is made even more difficult as the whole area is cluttered with pipes and cables. It’s also flooded with contaminated water.
“The detectors need to be big to observe something as big as a nuclear reactor,” says Haruo Miyadera, a scientist with Toshiba. “Taking them to the site and assembling them in a radioactive environment will be tough. We need to do more work.”
Another obstacle is the extremely high radiation being emitted by the surroundings. This creates noise that could disrupt the study by affecting the devices. If this happens, researchers won’t be able to correctly grasp the situation inside the reactors. These are just some of the issues that the studies must address.