Cosmic-ray muon scattering method to evaluate nuclear materials in fuel debris

Fuel debris was sampled by a trial retrieval method at Unit 2 of Fukushima Daiichi Nuclear Power Plant. To support safe handling and storage, it is important to distinguish fuel debris from other radioactive wastes and to sort it based on its nuclear material content. The muon scattering method is highly sensitive to high-atomic-number materials such as uranium. A prototype muon scanner was developed and tested to assess the uranium-dioxide content in simulated debris. For preliminary analysis, an analytical method that incorporates muon scattering angles, muon stopping rate, and debris weight was developed and applied.