Using muons to get a peek inside reactors

February 9, 2015

Elementary particle 'X-Ray' for Fukushima reactors

http://www3.nhk.or.jp/nhkworld/english/news/nuclear.html

Feb. 9, 2015 - Updated 13:07 UTC+1

Experts will use elementary particles bombarding the Earth to try to determine the location of melted nuclear fuel at the troubled Fukushima Daiichi nuclear power plant.

The project is aimed at finding clues as to the location of the melted fuel, a step that is indispensable to its removal from the damaged reactors, in order to continue with decommissioning work.

Three reactors at the plant suffered meltdowns following the massive earthquake and tsunami that struck the area in March of 2011. Extremely high radiation levels have been preventing experts from locating and determining the state of the melted fuel.

The experts will soon make use of a type of elementary particle called the muon to get a peek inside the reactors.

Workers wearing protective gear used a crane on Monday to install an observation device outside the Number 1 reactor building. The time they could devote to the task was limited, since radiation levels outside the reactor building are as high as 500 microsieverts per hour.

Muons are created when cosmic rays from space collide with the Earth's atmosphere. Scientists say about 10,000 muons per square meter reach the Earth's surface every minute.

Experts hope that observing the particles passing through the reactor building will create images of the nuclear fuel, in the same way an X-ray works.

After workers install another device at the Number 1 reactor on Tuesday, experts will conduct observations until March. It is believed that almost all the fuel in the reactor has melted and fallen down.

Experts also plan to use muons in a different way to probe the Number 2 reactor.

Fumihiko Takasaki, professor emeritus with the High Energy Accelerator Research Organization, led the development of the observation devices.

He said the project, which was started soon after the disaster happened, is finally being used at the plant. He said he hopes the technology will help with the decommissioning of the reactors by determining whether the fuel is still in them.