Since March 11, 2011, when the site suffered the double whammy of a magnitude 9 earthquake and tsunami, which triggered the meltdown of three of its reactors, Japanese officials has been struggling with how to deal with the cleanup. The high levels of radiation — more than that released from the atomic bomb explosions from Hiro shima and Nagasaki during World War II and the Three Mile Island and Chernobyl disasters combined — have made it difficult for anyone to get close enough to the reactors to inspect the damage.
But last May, LANL’s muon radiography team donned hazmat suits and got close enough to test a method that could be used to locate nuclear materials at the site.
The Japan Times reported last month that the team was able to place detectors — about 3 to 5 meters wide and just centimeters thick — near two of the damaged reactors.
A team member said the method lessens human exposure to radiation, as it can show conditions within the reactor while workers remain outside.
Konstantin Borozdin of Los Alamos’ Subatomic Physics Group said in a press release that, in the weeks following the disaster, the muon radiography team began investigating the use of a muon scattering method developed at LANL to gather images of nuclear material within the reactor cores. Additional study has confirmed the method would work and could be applied at Fukushima Daiichi.
“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.”
Muon radiography, also called cosmic-ray radiography, is analogous to X-ray imaging.
A muon is an elementary particle in the lepton family with a makeup similar to an electron, only much more massive. Countless muons constantly shower the earth, and the Los Alamos researchers found that by placing a pair of detectors in front of and behind an object, they could derive a detailed image of the muon scatter. Some materials, including uranium, have a greater scattering effect on the path of muons as they pass through them, so this method could help identify where molten nuclear fuel is located inside the reactors.
Borozdin was the lead author of a paper recently published in Physical Review Let ters that tested two methods of muon radiography to gather images of nuclear material within the core of reactors.
“As people may recall from previous nuclear reactor accidents, being able to effectively locate damaged portions of a reactor core is 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.”
The research paper was based on models that simulated Fukushima Daiichi Reactor 1 and not at the site itself.
“It’s conceptional at Fukushima, but the radiography is time-tested and in use elsewhere,” said James Rickman, a LANL spokesman. “We’ve proven the concept here at Los Alamos and different aspects have been tested all over the world.”
The same type of imaging has been used to detect pathways and chambers inside the pyramids of Egypt and to search beneath active volcanos. Rickman said muon radiography pioneered after the 9/11 attacks has also been applied in portal monitoring to detect potential smuggling of nuclear materials. Even heavily shielded contraband can noninvasively be detected without breaching the container.
Rickman said those in charge of the cleanup at Fukushima haven’t yet adopted the method devised at LANL.
“The Japanese have been discussing it. They are weighing possible options, and this is one of them,” he said.