One of the big problems with the cleanup at Fukushima is the fact that it is unknown exactly what the situation is inside the destroyed reactors because of the high levels of radioactivity. Specifically, the operators do not know where the melted cores are. I have mentioned in the past that it would be theoretically possible to use cosmic ray detectors to image the inside of the damaged reactors.
Cosmic rays consist mostly of highly energetic electrons and alpha particles generated by astrophysical processes such as supernova explosions. When they hit the Earth's atmosphere, they collide with atoms and decay into a variety of particles including neutrons, pions, positrons and muons. Muons are in the family of leptons and only weakly interact with normal matter. Thousands of muons hit every square meter of the Earth's surface every minute. Many of them travel deep into the Earth before they stop.
A team at the U.S. Los Alamos National Laboratories is working on a system that may allow imaging of the damaged Fukushima reactor cores. The basic idea is to dig holes and place two huge muon detectors on either side of the destroyed reactors at Fukushima. Muons will go through one detector, the general area where the cores are thought to be and then the other detector. Passing through the super dense core material will alter the path of the muons. When the readings from the two detectors are compared, they should provide an image of the area between the detectors.
The new Fukushima muon detectors are currently under construction. They are about twenty feet square and are encased in three inches of steel for protection against the high radiation outside the wall of the reactor. Normally, it would be best to place one detector above the core building and one under. However, given the problems with excavating a hole beneath the core building, the detectors will be placed on either side. This means that only a few of the incoming muons will be traveling horizontally and travel through the core and the detectors. Only a few thousand muons a day will be useful at Fukushima. The new muon detectors may be able to deliver muon data as early as this week but it will take months to build up detailed images.
A technique related to the Fukushima design is called muon stop tomography. This method only considers whether a muon passes through an area or is stopped by something that is very dense. This system has already been used to image volcanoes and the great Pyramid at Giza. This system has been used by other groups at Fukushima. However, it is believed that, considering the small size of the cores, the greater detail provided by the new muon system from LANL will be necessary to precisely locate the cores. The teams cleaning up Fukushima will need very detailed information about exactly where the small dense currently are in order to complete the cleanup.
Workers maneuvering a muon detector at Fukushima:
