Muon Imaging Present Status and Emerging Applications

X ray, neutron and gamma radiography have been widely used in industry as non-destructivetesting methods for industrial quality control and to assess the safety and integrity of structuresand components. These techniques use reasonably intense, artificial radiation sources (smallaccelerators or sealed isotopic sources) in laboratories and at industrial sites. Muonradiography, which is based on cosmic rays, is an alternative for certain applications that doesnot require artificial sources of ionizing radiation, and so is without regulatory constraints.High energy primary cosmic ray particles (mainly protons) interact with the nuclei composingthe Earth’s upper atmosphere to produce copious numbers of charged pi-mesons, which decayinto muons. Muons are similar to electrons in that they are elementary particles but withapproximately 200 times the mass. They interact with matter mainly through electromagneticforce and are easily capable of reaching the Earth’s surface. All other high energy chargedparticles, as well as gamma rays, are effectively shielded by the atmosphere so that muonsrepresent the vast majority of charged cosmic rays at the Earth’s surface.Some muons can penetrate hundreds of metres of rock and so can be used as a highlypenetrating, non-destructive natural probe. Muons can be readily used for imaging in situationswhere days or more of exposure time are available. Various techniques have been developedthat aim to measure the attenuation, transmission or scattering of the muon flux. Using these,information concerning the composition and dimensions of the materials encountered can beestimated.Numerous potential applications have been identified — ranging from examination of modernand ancient built environments, volcanology and industry, to nuclear security and safeguards— that have attracted attention around the world. This international interest led to a TechnicalMeeting held in Vienna in 2019, which was attended by 28 participants from 14 Member Statesand a representative from the European Commission. This publication is the output of thatmeeting

Investigation of muon tomography for re-verification purposes of spent fuel casks

The MUTOMCA (MUon TOMography for shielding CAsks) project is dedicated to investigate the suitability of muon tomography for the re-verification of loaded spent fuel casks. The loss of continuity of knowledge (CoK) in the hypothetical case that the containment and surveillance measures of EURATOM/IAEA would temporarily fail during the decades of dry storage of spent fuel, requires a technology for re-verification of the spent fuel enclosed in self-shielding casks. In such a case the inspectorates need to have a high degree of assurance on the amounts of nuclear material stored in the dual-purpose casks (casks for transport and storage). The re-verification is particularly challenging for conventional non-destructive-assay (NDA) methods, as the thick-walled CASTOR® V cask considerably attenuates the radiation emitted by the spent fuel. With the aim of proving the ability of muon tomography to detect a diversion of fuel assemblies in closed spent fuel casks, a two-module muon detector was designed, developed, constructed and commissioned. The detector, which is based on drift tube technology, was used in a field trial in the first months of 2023 in a dry storage facility in Germany to measure two CASTOR® V casks with different inventories. During the implementation of the field trial sufficient data was recorded to secure the evaluation of the capability of the muon tomography to fulfill the safeguards requirements for re-verification. Based on the results of the field test, this contribution will assess the potentials and the drawbacks of the experimental apparatus for the application of the reconstruction technique and will present a preliminary evaluation of the data. The MUTOMCA research project was established by INFN Padova and Forschungszentrum Jülich GmbH (FZJ) in collaboration with BGZ Company for Interim Storage (BGZ Gesellschaft für Zwischenlagerung mbH) and the European Commission, Directorate-General for Energy

EXPERIENCES IN SAFEGUARDING NUCLEAR REACTORS UNDER DECOMMISSIONING IN GERMANY

Regarding the complexity of safeguarding nuclear facilities under decommissioning, it is important to distinguish between item and bulk handling facilities. Item facilities such as power reactors do normally not have a hidden hold up of nuclear material that is recovered during the decommissioning of the facility. Consequently, the decommissioning steps for reactor facilities are straight forward. Once all spent fuel elements are removed, i.e., a permanently ‘shut down’ facility reaches the status of ‘closed down’, it remains without nuclear material that must be safeguarded. During the follow-up decommissioning process, the safeguards activities focus on the removal or rendering inoperable of essential equipment. The main objective at this stage is to reach the status of ‘decommissioned for safeguards purposes’. The paper describes and discusses experiences and technical challenges in safeguarding German nuclear reactors in their end-of-life stages from ‘shut down’ and ‘closed down’ to finally ‘decommissioned for safeguards purposes’