Muon detectors to look inside damaged reactors

October 19, 2012

Method spots radiation in reactors

Cosmic rays eyed to locate nuke fuel melt

http://www.japantimes.co.jp/text/nn20121019a1.html

Kyodo

WASHINGTON — Researchers from Los Alamos National Laboratory have developed a method to use cosmic rays to locate molten nuclear fuel within the crippled reactors at the Fukushima No. 1 nuclear power plant, the U.S. institute said Wednesday.

Monitoring data for a month or two by placing a pair of muon particle detectors in front of and behind the reactor buildings and the containment vessels will provide detailed images of the inside of the damaged reactors, it said.

A team from the New Mexico-based laboratory visited the Fukushima plant in May and confirmed they were able to place the detectors — about 3 to 5 meters wide and tens of centimeters thick — near the damaged reactors 1 and 2.

According to the U.S. laboratory, the team took note of muons that are generated when cosmic rays collide with atoms in the upper regions of the Earth's atmosphere. Massive numbers of muons shower the Earth every second.

Since muons are very light particles, they penetrate everything on Earth. But they change direction when they pass through heavy substances such as uranium and plutonium. Analyzing how they scatter can show what materials they passed through.

The newly devised method will allow images to be taken of the nuclear materials inside the reactors based on the scattering of muons.

Japan is struggling with decommissioning the Fukushima reactors due to the high amount of radiation at the power plant, which was crippled by the March 11 earthquake and tsunami last year.

Haruo Miyadera, a member of the research team, said the new method will lessen human exposure to the high radiation as it can show conditions in the reactor cores while workers stay outside.

"If we find where the molten nuclear fuel is located, it will give us a clue to understand what happened inside the reactors and help accelerate the decommissioning work," he said.

In addition to its potential utility at the Fukushima nuclear plant, the muon radiography method has been deployed to detect potential smuggling of clandestine nuclear materials in the United States, the institute said.