Muon tomography is a technique that harnesses naturally-occurring cosmic radiation, specifically muons, to provide information on density contrasts in otherwise difficult to access locations. Muon tomography exploits the significant flux (typically 160 per square metre per second) of muons produced in the atmosphere. Muons are highly penetrating particles capable of penetrating many hundreds of metres of rock. They are preferentially absorbed by denser material and so, via a process similar in principle to an X-ray, are able to return information on density changes in an overburden.

The application of muon tomography to repository monitoring presents several distinct advantages: it operates non-invasively, enables continuous data collection, can image large volumes of rock, and provides sensitivity to density variations that might indicate structural changes or anomalies. As such, it is a powerful and relevant technique that can deliver both unique and complementary (to other techniques) data to aid both safety and safeguarding within any long-term storage repository.

The presentation will report on a significant body of work carried out by the authors to assess the relevance of muon tomography to the safety and safeguarding agendas. In order to make this study as realistic as possible a sophisticated geological digital twin of an existing repository analogue, namely the Grimsel Test Site (GTS) in Switzerland, has been created and a number of scenarios have been considered - all of which assume the deployment of existing muon sensors.

Three primary scenarios were considered, specifically:

1. the detection of voids and karst-like features were introduced into the Grimsel geology within the digital twin. Karst formations, ranging from 10 m to 25 m in diameter, were found to be detectable at depths of 20 m with a small area detector, with detection times ranging from days to a year depending on the fraction of material infill within the void.

2. the detection of incomplete backfill. In this case the Grimsel Test Site HotBENT geometry was modelled to consider how muon tomography can be used to image structural defects. In this case, air voids within bentonite backfill were detectable with high confidence. A near linear relationship was found between air gap size and detection rate.

3. the detection of plug damage. Cylindrical voids within the concrete containment plugs were modelled to assess potential damage detection. A 1 m diameter void was detectable within approximately 5 months with 20 detector bundles. Detection times decreased exponentially with increasing detector array size.

A full summary of the results from this programme of work will be presented alongside a description of the types of muon sensor that were assumed for these studies. The presentation will also summarise the list of safety and safeguarding challenges that the authors believe muon tomography can address. Finally, the presentation will conclude with a summary of plans for a experimental programme of work that is proposed for the GTS in order to fully assess the use of muon tomography in such an environment.

How to cite: Thompson, L., Aymanns, K., Liebscher, A., Mandel, M., Martin, A., Mildebrath, M., Niemeyer, I., and Steer, C.: The application of muon tomography to monitoring safety andsafeguarding in nuclear waste storage and emplacement, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-36, https://doi.org/10.5194/safend2025-36, 2025.

Nuclear power plants generate spent nuclear fuel (SNF) during operation. This spent fuel requires long-term safeguarding during interim storage and final disposal to ensure the non-proliferation of fissile materials. These safeguards measures for spent fuel storage facilities (SFSFs) include a combination of material accountancy, containment and surveillance (C/S), and design information verification (DIV), combined with regular inspections to verify declarations at random intervals.

In recent years, antineutrino detection techniques have been proposed and prototyped for reactor safeguards, utilising the antineutrino emission from the continuous beta decay of fission fragments within nuclear fuel. One of the key features of interest is the ability of antineutrinos to pass through dense material - such as shielding, facility walls or geology - unhindered. The detection techniques employed for reactor antineutrinos can also be adapted to SNF but due to the extended cooling time of SNFs the antineutrino flux tends to be lower by two or more orders of magnitudes and the emitted lower in energy, requiring adaptation to the facilities and scenarios in question.

In this study, the antineutrino emissions of SNF are simulated and modelled for a range of different SNF ages and distribution in SFSFs to determine the expected signal in various types of detectors, including scintillation detectors and time projection chambers (TPCs) filled with liquid organic (LOr) target media. Using this simulation framework, various levels of background activity are analysed to estimate detector sensitivity in various usage scenarios, including passive continuous monitoring, re-verification of facilities or specific containers. This study then compares the feasibility of antineutrino-based detection approaches and formulates minimum technical requirements (e.g. background levels, detection efficiency) required for the safeguards monitoring of SNF.

How to cite: Schnellbach, Y.-J., Niemeyer, I., Roth, S., and Göttsche, M.: Antineutrino Detection for Safeguards: Concepts and Feasibility for Storage Facilities, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-122, https://doi.org/10.5194/safend2025-122, 2025.