Top > Releases ・ Announcements > Fukushima Daiichi NPS Prompt Report > 2015 > Recent topics:COSMIC "MUON" RAYS TO LOOK INSIDE FUKUSHIMA REACTORS AS TEPCO BEGINS TESTING

Fukushima Daiichi NPS Prompt Report 2015


Cutting edge technology will be used to explore condition of reactor cores, an essential step toward their removal

FUKUSHIMA, February 9 2015 -A first-of-its kind device that will use cosmic rays to help learn essential information about the state of the damaged reactor cores is ready for testing at Fukushima Daiichi Nuclear Power Station, the Tokyo Electric Power Company announced today.

The device, which will be tested at the Unit 1 reactor, will use "muons," a type of cosmic ray that constantly bombards Earth. While muons permeate light objects easily, they are blocked by heavy substances such as uranium. It is believed that scientists can take advantage of that difference to create an image of the fuel condition inside of the reactor, much as an X-ray creates an image of human bones. In the past, muon technology has been used to discover the condition of magma inside a volcano.

"This is a great example of how the innovation and cooperation from external experts is helping us overcome challenges and make progress toward decommissioning." said Naohiro Masuda, Chief Decommissioning Officer. "I hope that this will give us an opportunity to contribute to technological advancement and to share such progress with the rest of the world."

An essential task in decontaminating and decommissioning Fukushima Daiichi is the eventual removal of the fuel debris from Units 1, 2, and 3. But before those reactor cores can be removed, it is essential to locate where the debris has dropped inside the reactor. However, the radiation level around the reactors is too high for human beings to look inside to confirm the data. To overcome this obstacle, the physics community has proposed that TEPCO use muon technology, This initiative has been jointly developed by IRID (International Research Institute for Nuclear Decommissioning) and other domestic and foreign institutions.

The apparatus that will be used in the Unit 1 test was developed by Japan's High Energy Accelerator Research Organization, also known as KEK, and will be using the so-called permeation method to measure the Muon data. The analysis of the findings is scheduled to be completed by the end of March.

"As scientists, we feel we have a responsibility to use our knowledge and skills to help the decommissioning process proceed as fast as possible," Fumihiko Takasaki, a professor emeritus at KEK who leads the project, said.

TEPCO is planning a second proving test in the coming months at Unit 2, using another method of muon technology.  The company said it will continue to collaborate with experts inside and outside Japan to quickly and accurately obtain information on the status of the reactor cores.

Photos and video of the set-up of the apparatus are posted at


Tokyo Electric Power Company, Inc. (TEPCO) is Japan's largest power company, supplying energy to the greater Kanto area, including Japan's two most populous cities, Tokyo and Yokohama. Its 35,000 employees are committed to providing safe, reliable power to its 29.0 million customers, diversifying energy resources to ensure sustainability, and contributing to economic growth while fully meeting its responsibilities after the Fukushima Daiichi accident.
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