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Cosmic Rays offer potential aid to Japan's reactor cleanup

Posted: 22 Oct 2012 ?? ?Print Version ?Bookmark and Share

Keywords:muon radiography? Fukushima Daiichi? nuclear power? cosmic-ray?

A method to use cosmic rays to gather detailed information from inside the cores of nuclear reactors

damaged by the earthquake in Japan has been devised by researchers from the Los Alamos National Laboratory.

On March 11, 2011, the reactors at Japan's Fukushima Daiichi nuclear power plant suffered heavy damages from the tsunami that followed the earthquake. Researchers at Los Alamos, say that their scattering method for cosmic-ray radiography shows great promise for pinpointing the exact location of materials within the Fukushima reactor buildings.

Konstantin Borozdin of Los Alamos' Subatomic Physics Group is the lead author of a paper on the topic that appears in the journal Physical Review Letters. The paper compares two methods for using cosmic-ray radiography to gather images of nuclear material within the core of a reactor similar to Fukushima Daiichi Reactor No. 1.

Figure: Los Alamos National Laboratory Muon Radiography team members stand in front of the damaged Fukushima Daiichi reactor complex during a visit to determine evaluate whether Los Alamos' Scattering Method for cosmic-ray radiography could be used to image the location of nuclear materials within the reactor buildings.
Source: Los Alamos.

"As people may recall from previous nuclear reactor accidents, being able to effectively locate damaged portions of a reactor core is a key to effective, efficient cleanup," Borozdin said. "Our paper shows that Los Alamos' scattering method is a superior method for gaining high-quality images of core materials."

Muon radiography (also called cosmic-ray radiography) uses secondary particles generated when cosmic rays collide with upper regions of Earth's atmosphere to create images of the objects that the particles, called muons, penetrate, according to Los Alamos. The process is analogous to an X-ray image, except muons are produced naturally and do not damage the materials they contact, the researchers say.

Muon radiography key to gathering data
By placing a pair of muon detectors in front of and behind an object, and measuring the degree of scatter the muons underwent as they interacted with the materials they penetrated, Los Alamos researchers found that they were able to take detailed images. The method works particularly well with highly interfering materials such as uranium, the researchers said.

Using a computer model, the research team simulated a nuclear reactor with percentages of its core removed and placed elsewhere within the reactor building. They then compared the Los Alamos scattering method to the traditional transmission method. The simulation showed that passive observation of the simulated core over six weeks using the scattering method provided high-resolution images that clearly showed that material was missing from the main core, as well as the location of the missing material elsewhere in the containment building.

In comparison, the transmission method was barely able to provide a blurry image of the core itself during the same six-week period, according to the Los Alamos researchers.

"We now have a concept by which the Japanese can gather crucial data about what is going on inside their damaged reactor cores with minimal human exposure to the high radiation fields that exist in proximity to the reactor buildings," Borozdin said. "Muon images could be valuable in more effectively planning and executing faster remediation of the reactor complex."

- Dylan McGrath
??EE Times

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