Cosmic ray muon computed tomography of spent nuclear fuel in dry storage casks

Abstract

Radiography with cosmic ray muon scattering has proven to be a successful method of imaging nuclear material through heavy shielding. Of particular interest is monitoring dry storage casks for diversion of plutonium contained in spent reactor fuel.Using muon tracking detectors that surround a cylindrical cask, cosmic ray muon scattering can be simultaneously measured from all azimuthal angles, giving complete tomographic coverage of the cask interior. This paper describes the first application of filtered back projection algorithms, typically used in medical imaging, to cosmic ray muon imaging. The specific application to monitoring spent nuclear fuel in dry storage casks is investigated via GEANT4 simulations. With a cylindrical muon tracking detector surrounding a typical spent fuel cask, the cask contents can be confirmed with high confidence in less than two days exposure. Similar results can be obtained by moving a smaller detector to view the cask from multiple angles. a) Corresponding author.

A generalized muon trajectory estimation algorithm with energy loss for application to muon tomography

“…Existing detectors for muon tomography measure the locations and directions of incoming and outgoing muons. The detectors are typically parallel planes of position sensitive chambers, such as scintillators [2] drift-wire chambers [3,4] or gas-electron multiplier detectors, although cylindrical detectors have also been proposed [22]. A typical configuration of some detectors and an imaged object in muon tomography applications is shown in Figure 1.…”

“…Using fewer muons provides significant time savings but lower quality images, while a higher number of measured muons results in improved image contrast and resolution but increased measurement time. Existing studies on muon-CT detectors have demonstrated that muons on the order of millions (requiring minutes to days of measurement time, depending on the size and orientation of the detectors) are required for imaging large scale objects such as cargo containers [4,5,11] or dry casks [21][22][23]. Recent work based on simulations showed that several days (>10 6 muons) are needed to identify the location of spent nuclear fuel in dry casks [21][22][23].…”

“…Some of the challenges of muon tomography are low muon flux at 10,000 muons/s/cm 2 , difficulty in muon momentum measurement due to high energy (>1 GeV) and velocity leading to low energy loss per unit length, and the substandard resolution of the available imaging reconstruction algorithms [19][20][21][22][23][24]. In addition, recent efforts exploring muon computed tomography (μCT) are limited by the tendency of muons to scatter in the target, thus blurring the image.…”

“…Current reconstruction algorithms rely on simple assumptions for muon path estimation through the imaged object. One common assumption is to use a straight-line path defined by the line between the intersection of the entry and exit path lines [22,23]. Another commonly used assumption is based on the calculation of the point of closest approach (PoCA) between the incoming and outgoing trajectories [20,21].…”

Atmospheric muons as an imaging tool

“…However, the optimal geometry for specific use cases can vary, as shown for example in Ref. [87] where the upstream and downstream tracking systems are positioned on the sides of a large cylindrical cask of spent nuclear fuel (Fig. 4, top right).…”