Scientists: Cosmic rays can see through nuclear reactor, locate fuel

January 24, 2014

By JIN NISHIKAWA/ Staff Writer

Japanese scientists have developed a method to use cosmic rays to see through a nuclear reactor, raising hopes for locating and accounting for melted fuel inside the crippled Fukushima nuclear plant.

“Installing several sensors outdoors for a month or so is enough to get a picture of internal structures,” said Fumihiko Takasaki, a particle physics scientist at the High Energy Accelerator Research Organization. “Our technology is well established, so I hope it will be used to help decommission the stricken reactors at the Fukushima No. 1 nuclear power plant.”

Takasaki and his co-workers installed sensors outdoors at the Tokai No. 2 nuclear power plant in Ibaraki Prefecture between February 2012 and December 2013 to detect muon particles contained in cosmic rays. Muon beams, which are absorbed more easily in high-density materials such as uranium, can be used to obtain see-through images, much in the way of X-ray radiography.

The measurements allowed the scientists to outline the shape of the reactor containment vessel, locate the fuel storage pool and size up the amount of nuclear fuel being stored. The perspective images clearly showed the fuel was stored in two separate sections in the storage pool.

At the Fukushima plant, high radiation levels are preventing workers from staying for a long time inside the No. 1, No. 2 and No. 3 reactor buildings, where meltdowns occurred following the March 2011 Great East Japan Earthquake and tsunami.

Tokyo Electric Power Co., the plant operator, has yet to learn where the nuclear fuel currently lies. The locations and amounts of the melted nuclear fuel should be identified by the time the government and TEPCO plan to start extracting it in the first half of fiscal 2020.

Even if the melted fuel has escaped into the basement levels, it can still be located by installing sensors in underground holes, the scientists said. Each sensor unit weighs 800 kilograms, not including the steel sheets for shielding radiation, and costs around 20 million yen ($200,000), they added.

By JIN NISHIKAWA/ Staff Writer
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The Asahi Shimbun

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  • A graphic image showing the locations of nuclear fuel in a storage pool (box in the foreground) at the Tokai No. 2 nuclear power plant, relative to the reactor containment vessel (background) (Provided by the High Energy Accelerator Research Organization)

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