Designing a muon scattering scanner for nuclear debris measurement.

Removal of fuel debris is planned to start at Unit 2 of the Fukushima Daiichi Nuclear Power Plant. During the removal, it is desirable to distinguish fuel debris from radioactive wastes and to sort the fuel debris accordingly to the amounts of nuclear material contained. Muon scattering tomography invented at Los Alamos in the early 2000s is highly sensitivity to high-atomic-number materials such as uranium. A muon scanner to sort the debris is designed and currently in production. One of the challenges is to operate the muon scanner in the presence of high γ-ray radiations from the debris: muon-event-identification electronics and a muon-tracking algorithm in the presence of high γ-ray radiations were developed.

Simulation and validation studies of a large drift tube muon tracker.

Cosmic ray muons are massive, charged particles created from high energy cosmic rays colliding with atomic nuclei in Earth's atmosphere. Because of their high momenta and weak interaction, these muons can penetrate through large thicknesses of dense material before being absorbed, making them ideal for nondestructive imaging of objects composed of high-Z elements. A Giant Muon Tracker with two horizontal 8 × 6 in.2 and two vertical 6 × 6 in.2 modules of drift tubes was used to measure muon tracks passing through samples placed inside the detector volume. The experimental results were used to validate a Monte Carlo simulation of the Giant Muon Tracker. The imaging results of simulated samples were reconstructed and compared with those from the experiment, which showed excellent agreement.

Application of muon tomography to fuel cask monitoring.

Long-term monitoring of spent fuel stored in dry cask storage is currently achieved through the use of seals and surveillance. Muon tomography can provide direct imaging that may be useful in cases where what is known as Continuity of Knowledge (CoK) has been lost using the former methods. Over the past several years, a team from Los Alamos National Laboratory has been studying the use of muon scattering and stopping to examine spent fuel in dry cask storage. Data taken on a partially loaded Westinghouse MC-10 fuel cask have demonstrated that muon scattering radiography can detect missing fuel assemblies. A model, validated by this data, shows that tomographic reconstructions of the fuel can be obtained in relatively short exposures. Model fitting algorithms have been developed for dealing with datasets with limited angular that appear to work well. Here we show that muon tomography can provide a fingerprint of a loaded fuel cask, because of its sensitivity to both the density and atomic charge of the spent fuel, and that it is sensitive to many diversion scenarios.This article is part of the Theo Murphy meeting issue 'Cosmic-ray muography'.