The use of muon radiography in safeguarding geological repositories

Abstract. Muon radiography is a technique that harnesses naturally occurring cosmic
radiation to noninvasively determine the density of an object of interest. The
technique has many similarities to that of medical X-ray examinations and can
supply detailed density maps of the object. We propose the application of muon
radiography to aspects of the long-term monitoring of nuclear waste. In
particular, muon radiography would provide valuable information on the
overburden of a prospective underground geological repository and would be
able to identify unknown features, such as undocumented underground
passages. Similarly, muon tomography is capable of confirming that containers
that have nominally been emptied are in fact empty. Such safeguard measures
are important to maintain continuity of knowledge and to develop robust
deterrent strategies against the removal of monitored nuclear material. The presentation focuses on the results of simulations that address some of
these questions. Details of assumptions regarding the detector requirements
and run times necessary to perform the imaging are discussed and results from
the various removal and misuse scenarios are presented.



Muons and Muon Tomography
What is muon tomography?
• Works in exactly the same way as medical x-ray imaging • A beam of x-rays (muons) passes through the object of interest • A "detector" (film or digital system) is placed on the other side of the object of interest • Density differences in the object are evident in the "image" • However there are differences: muons are free and more penetrating than X-rays

Applications of Muon Tomography Muon Tomography and Geological Repositories (GRs)
• Civil infrastructure imaging and imaging of ore bodies in mines with muons is already underway • For example: in the UK the technique is being used to search for hidden shafts in railway tunnels • Elsewhere in the world nickel and uranium ore bodies • Works in exactly the same way as medical x-ray imaging • A beam of x-rays (muons) passes through the object of interest • A "detector" (film or digital system) is placed on the other side of the object of interest • Density differences in the object are evident in the "image"

Muon scattering tomography ("MST")
• By placing muon detectors both above and below (or either side) of the object of interest additional information (about the nuclear composition) of the object being imaged can be determined

Material ID in Heterogenous Waste Drums
A method has been developed to perform material identification using machine learning techniques STEP 1: identification of material boundaries in the waste drum which has a concrete matrix STEP 2: uses machine learning MVA algorithms to assign a probability for each identified object being a particular material.See https://arxiv.org/abs/2012.01554 Possible applications to GRs: • safeguarding any outgoing potentially-empty package (e.g.MST would be able to confirm, quickly, any presence of high-Z material in the outgoing package that shouldn't be there) 1 2

Safeguards Applications
Looking at the potential for muon scattering tomography to identify possible changes to a CASTOR drum • Muon tomography is a powerful tool that exploits naturally occurring radiation to form images of objects in a non-invasive and non-destructive way • It has been famously used to search for hidden chambers in pyramids and to image the magma chambers in volcanoes • The technique is currently applied globally to a huge range of applications including imaging of civil infrastructure, mines, nuclear safeguards and material control, homeland security • Within the management of nuclear waste there are a number of areas where muon radiography is a promising technology to address specific problems such as geological repository design information verification, integrity assurance and longterm monitoring • Similarly, muon scattering tomography offers the possibility to identify issues such as material diversion, package voiding and material identification.

Conclusions
are being located without the need for drilling boreholes • In general muon tomography is a powerful tool for locating irregularities in overburdens • Initial proof of principle studies have simulated the ability to detect a large unknown shaft in a GR with a single detector • CAVEAT: going deeper requires large area detectors and/or long measurement times Void present No void present Muon Tomography and Geological Repositories (GRs) • Other studies have looked at the detectability of an unknown feature in the GR as a function of the solid angle that the feature presents at the detector • Note: multiple detectors plus imaging techniques such as SART and/or use of machine learning methods should considerably reduce the time needed to detect a feature Possible application to GRs: • design information verification • continuous geological overburden monitoring for overburden change detection • understanding the condition of the host geology • searching for undocumented voiding • checks of backfill integrity in the vaults • tunnel lining system checks/monitoring • sensitivity to water ingress and movement in the overburden • long-term monitoring of the GR post-closure REMINDER: muon tomography is non-invasive and nondestructive COMMENT: data fusion from seismic and muon radiography studies will be beneficial in some of these applications (resolves all material properties) Muon Radiography ("Muography") can form within the matrix of a waste drum and are a concern.Using muon scattering tomography bubbles can be identified and their volume accurately determined Possible application to GRs: • monitoring of in-package voidage within nuclear waste drum which may result as a consequence settlement in the package during transportationThis project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 755371.
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 755371.Diversion Scenarios considered: 1.Empty basket 2.Half-loaded basket (Unloaded side fuel assemblies) 3.Half-loaded basket (Unloaded centre fuel assemblies) 4.Pb pellets basket (UO 2 pellets replaced by Pb pellets) This is not a new technique, it was first used to measure tunnel overburdens in 1955 and has been famously used to image pyramids and the magma chambers of volcanoes