Analysis of Spent Nuclear Fuel Imaging Using Multiple Coulomb Scattering of Cosmic Muons

Abstract

Cosmic ray muons passing through matter lose energy from inelastic collisions with electrons and are deflected from nuclei due to multiple Coulomb scattering. The strong dependence of scattering on atomic number Z and the recent developments on position sensitive muon detectors indicate that multiple Coulomb scattering could be an excellent candidate for spent nuclear fuel imaging. Muons present significant advantages over existing monitoring and imaging techniques and can play a central role in monitoring nuclear waste and spent nuclear fuel stored in dense well shielded containers. The main purpose of this paper is to investigate the applicability of multiple Coulomb scattering for imaging of spent nuclear fuel dry casks stored within vertical and horizontal commercial storage dry casks. Calculations of muon scattering were performed for various scenarios, including vertical and horizontal fully loaded dry casks, half loaded dry casks, dry casks with one row of fuel assemblies missing, dry casks with one fuel assembly missing and empty dry casks. Various detector sizes (1.2 m x 1.2 m, 2.4 m x 2.4 m and 3.6 m x 3.6 m) and number of muons (10 5 , 5·10 5 , 10 6 and 10 7 ) were used to assess the effect on image resolution. The Point-of-Closest-Approach (PoCA) algorithm was used for the reconstruction of the stored contents. The results demonstrate that multiple Coulomb scattering can be used to successfully reconstruct the dry cask contents and allow identification of all scenarios with the exception of one fuel assembly missing. In this case, an indication exists that a fuel assembly is not present; however the resolution of the imaging algorithm was not enough to identify exact location.*Corresponding author: schatzid@purdue.edu I. INTRODUCTIONSince the pioneering work of E.P. George [1] and L. Alvarez [2], relativistic muons have been shown to have the ability to penetrate dense materials and by monitoring the subsequent scattering and/or attenuation of muons, a measurable signal about the structure and composition of the interrogated material can be obtained [3]. Recently, cosmic ray muons have been investigated for volcano imaging and cargo scanning applications and their use has been extended to nuclear waste imaging and determination of molten nuclear fuel location in nuclear reactors having suffered from the effects of a severe accident similar to the one happened in Fukushima [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].Earlier muon radiographic techniques were based on attenuation principles. A new promising method based on multiple Coulomb scattering was developed and demonstrated at LANL for detection of high-Z materials hidden in a large volume of low-Z materials, a situation representative of shielded material shielded hidden in a cargo container [24,25]. It was suggested that muon momentum measurement which can be achieved by indirectly measuring muon scattering in several layers of materials with known thickness could improve image resolution.This was later demonstrate...

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

“…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].…”

“…To simulate MCS, Geant4 implements a non-Gaussian model that is validated with experimental data [15,21], and it is used in the paper as a tool to test the proposed GMTE algorithm. Due to the interest in using cosmic ray muons in spent nuclear fuel storage cask assay, uranium represents high-Z material, iron represents medium-Z material, and concrete represents low-Z material.…”

“…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.…”

“…The estimated muon path asymptotically approaches the incoming and outgoing muon trajectories. The algorithm was tested under various scenarios using detailed Geant4 Monte Carlo [15,21,26] simulations. It is hypothesized that the proposed generalized muon trajectory estimation (GMTE) algorithm will produce muon tomographic images with improved quality and reduced noise, requiring fewer muons than the muon reconstruction techniques that are currently available.…”

Muography of different structures using muon scattering and absorption algorithms

“…A similar application for mapping cultural heritage sites was proposed in the 1970s by L. W. Alvarez to inspect the Chefren pyramid for hollow vaults [11], and very recently implemented with spectacular results [12]. The technique has been successfully applied to volcano inspections to characterize the inner structures and lava domes [13][14][15][16][17], to mining [18], to archaeology [19], including tunnel searches [20], geological surveys [21,22], nuclear waste [23][24][25][26] and reactor monitoring [27,28].…”