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Part 4 of 5 Parts (Please read Parts 1,2 and 3 first)
     Aymanns contacted Paolo Checchia at the Legnaro National Laboratory in Padua, Italy. Checchia and colleagues are also researching muon detectors constructed with drift tubes. Their work is based on technology that was developed for Compact Muon Solenoid detectors at the CERN laboratory in Geneva, Switzerland. They have computer simulations that shows that is theoretically possible to spot if a fuel assembly has been removed from a dry cask. They have created a prototype detector that contains sixty-four drift tubes in eight layers.
     Last year, Checchia and colleagues performed tests that were partly funded by Euratom which is the organization that is responsible for monitoring spent nuclear fuel within Europe. For these tests, a prototype detector was attached to a dry cask at the Neckarwestheim nuclear power plant near Stuttgart. They were not able to make a detailed study of the contents of the test casks. However, the team did show that they could detect muon behavior above the faint radiation from the contents of the cask. They will need to make bigger detectors to determine the presence or absence of fuel assemblies in dry casks.
   Finland and Sweden could definitely benefit from muography. Both of these countries are developing geological repositories for spent nuclear waste. Morris and his team have computer simulations that show that it should be possible to identify missing or replaced fuel assemblies with only twenty-four hours of muon tracking in the copper and iron casks that will be used in Scandinavia. The researchers say that carrying out these measurements immediately before burying the dry casks would be “the last chance for inspectors to evaluate state declarations of spent fuel disposal”.
    Muons can be used to images other types of nuclear waste beyond spent nuclear fuel. One of these is the metal cladding of the tubes that contain the uranium pellets which has to be removed when spent nuclear fuel is reprocessed. In the U.K. there are tens of thousands five hundred liter stainless-steel drums full of fuel rod cladding that is encased in concrete.
    Ralf Kaiser works at the University of Glasgow. He says that some cladding-filled drums have been bulging. This suggests that there may be some spent nuclear fuel in the drum. Uranium has a tendency to expand when it oxidizes which could account for the bulging. Since the drums are hard to access, it is difficult to know how many drums might contain spent nuclear fuel. Bulging might result in drums cracking open which could release radioactive materials. The ability to identify which drums contain spent fuel could help prevent such leaks.
      Kaiser and his colleagues at the University are working on muon detectors that consist of thousands of plastic scintillating fibers. Collaborating with researchers from the National Nuclear Laboratory at the Sellafield reprocessing plant, the Glasgow team first created a small prototype followed by a full-sized system that could hold one five hundred liter drum. A series of laboratory tests from 2015 on showed that the system could image a range of objects inside one of the concrete drums. This included detection of a one-inch long cylinder of uranium.
Please read Part 5