Conference Agenda

Mass spectrometric measurements on uranium samples taken in nuclear facilities and their surrounding environment can provide a wide range of important information about activities being carried out in these facilities. Not only the degree of uranium enrichment (²³⁵U/²³⁸U) can be determined, the ²³⁶U/²³⁸U isotopic ratio is a widely used tracer, which provides sensitive information on source identification for safeguard purposes, nuclear forensics studies and environmental monitoring [1]. An additional strong tool in nuclear forensics is the ²³⁰Th/²³⁴U chronometry. The method relies on the fact that uranium ore processing and further chemical purification of uranium (i.e. for enrichment) removes almost all impurities, including all radioactive decay products. In the case of the ²³⁰Th/²³⁴U chronometer the decay of ²³⁴U with a half-life of 245,500 years to ²³⁰Th is used for age determination. Measuring the parent-daughter ratio in the sample, and assuming a quantitative separation of impurities and daughter isotopes from the U-solution, the decay equations can be applied to calculate the time elapsed since the date of the last purification. This method was developed for the age-determination of samples with high ²³⁵U enrichment, and therefore comparably high ²³⁴U contents, and for large sample quantities of several milligrams [2].

For the detection of undeclared activities in nuclear facilities, swipe and environmental samples are taken containing only traces of uranium bearing microparticles which can be analyzed for isotopic composition. In the case that undeclared activities are detected, the time when these activities have happened needs to be verified. Therefore, more sensitive analytical methods must be developed for a reliable ²³⁰Th/²³⁴U age-dating application [3]. Advanced mass spectrometry methods like SIMS with large-geometry instruments are considered the preferential analytical methods to determine the isotopic composition of these environmental samples with a very high precision [4]. The successful development and establishment of a method for age-dating application mainly relies on the accessibility of well-designed reference materials that are not only used for calibration of the analytical device, but also for the determination of important measurement parameters, such as the relative sensitivity factor.

This presentation will provide some general background information about the analyses of microparticulate samples containing known uranium isotopic ratios and Th abundances with a focus on the development of reference particles with well-defined properties designed particularly for new age-determination applications.

Literature: [1] Diez-Fernández, H.,et al.: Talanta 206 (2020) 120221. [2] Vargas, Z., et al.: Applied Radiation and Isotopes 102 (2015) 81-86. [3] Szakal, C., et al.: Analyst 144(14) (2019) 4219-4232. [4] Groopman, E. E., et al.: Journal of Analytical Atomic Spectrometry 37(10) (2022) 2089-2102.

There are currently numerous innovative nuclear reactor designs being proposed as part of what could be the next era of commercial nuclear energy production. Many of them follow a trend of reducing construction and footprint scale by increasing compactness and integration. Such is the case of Small Modular Reactor (SMR) concepts, a subcategory of Novel Advanced Reactors (NARs), conceived for modular production, transportation and assembly. Another key feature of various NAR designs is the use of novel fuels such as TRISO (graphite-coated uranium pebbles) or liquid salts with fuel cycles different from the traditional uranium one. As opposed to uranium fuel rods, these alternatives are to be employed as bulk materials, sometimes in constant flow, and in some cases are foreseen to remain enclosed within the reactor for its entire lifetime. While offering economic, practical and temporal advantages, these atypical structures and fuels in NARs make them, at present, more opaque to external examination. Thus posing the challenge of developing corresponding novel measuring and inspection techniques to quantify and monitor NAR reactor inventories for safeguards purposes, amongst others.

The study being presented addresses this challenge by considering Nuclear Resonance Fluorescence (NRF) as a tool for the non-destructive probing of NARs, with the objective of identifying and quantifying specific fuel isotopes relevant to non-proliferation verification. NRF is a process in which a sample of interest is irradiated with a beam of high-energy photons. The nuclei in the sample absorb a fraction of the high-energy photons and subsequently emit further high-energy photons that can escape the material and thus be detected. The energy of the emitted photons depends on the emitter’s nuclear structure and can therefore be used as a signature to identify specific isotopes. Making the technique appropriate for the detection and quantification of fissile material within a non-fissile environment. Since the energies of the photons are high enough to travel through shielding materials, this method could be potentially used to non-destructively inspect the interior composition of objects such as NARs.

A feasibility analysis of this promising application of NRF is being carried out with a focus on the interaction between high-energy photon beams and the specific shielding materials that can be present in such reactors. The comprehensive classification of these materials across predominant NAR designs is used as a starting point to determine the properties relevant to NRF and the availability of corresponding experimental data. Followed by the investigation of photon beams in equivalent bulk material combinations, conducted through preliminary computer simulations. Therein including the identification of limiting factors such as the absence of data and the characteristics of photon sources and detectors necessary for the practical implementation of NRF measurements in this context. An initial assessment is thus presented of the potential advancement of the NRF measuring approach as a NAR non-proliferation verification technique.

New types of nuclear reactors are being actively developed in several countries and considered as future sources of low-carbon electricity. Among these, especially the concept of “Small Modular Reactors” (SMRs) has gained traction in policy and investment circles, for domestic or export use. These concepts, if successful, not only foresee an overall increase in nuclear capacity but also an increase in nuclear sites, thanks to the more flexible deployment plans. Furthermore, many of these concepts intend to use nuclear fuel with higher-than-before uranium enrichment to offset the technical drawbacks of smaller reactor sizes. This potential increase in number of reactors and sites combined with the higher fissile material content in the fuel (up 20% instead of 3-5%) leads to new proliferation concerns. Traditional non-proliferation safeguards are centered on large facilities with large inventories and long breakout times, due to the low enrichment. A shift away from this model requires a rethinking of effective safeguards, especially due to the logistical and budgetary restraints on a safeguards inspectorate.

In the last decade, there have been advancements in monitoring nuclear power plants using the antineutrino emissions of active reactor cores, including the successful deployment of tonne-scale prototypes at traditional large nuclear power plants. Antineutrinos are produced by the fission fragments produced in an active reactor. These emissions are a continuously emitted spectrum directly tied to the core content, i.e. a spectral measurement can provide a “fingerprint” of the plutonium and uranium content. Additionally, antineutrino emissions are impossible to shield effectively, allowing for reactor monitoring at a stand-off distance of up to tens of meters and outside the reactor building itself – making it highly attractive as potential safeguards tool for monitoring sites autonomously and non-intrusively.

In the first stage of the nuSENTRY project, OpenMC-based simulations of future reactor types, chiefly SMRs and related compact reactors – such as naval reactors – are conducted to understand the expected antineutrino spectra of an SMR-like reactor throughout the entire fuel/reactor lifecycle. These findings will be used to understand the applicability of existing and future antineutrino detection technologies for these new types of reactors. In future stages of the nuSENTRY project, these reactor simulations will be combined with Geant4-based detector simulations to evaluate the feasibility of antineutrino detection as safeguards tool for SMR installations. Different detection approaches will be compared as new detector R&D can potentially provide directional discrimination of reactors – a boon for SMR-type sites with multiple reactors in a small area. Furthermore, it is also planned to consider the use of secondary signatures present at a nuclear site, including long-term neutron measurements or use of cosmic muons for building imaging, to enhance confidence in the antineutrino measurements.

Fusion energy systems, while avoiding the use of fissile materials such as highly enriched uranium and plutonium, still pose certain proliferation risks. Key concerns include the diversion of tritium for military purposes, the production of weapon-grade plutonium using fusion neutrons, and the dual-use potential of laser/inertial confinement fusion facilities for nuclear weapons development. This talk examines these risks with a focus on material monitoring challenges, the technical feasibility of plutonium breeding in fusion reactors, and the role of advanced experimental and computational methods in circumventing nuclear test bans. Strategies for mitigating proliferation risks include the integration of safeguards-by-design in early-stage reactor concepts, international standardization of monitoring frameworks, and fostering dialogue between fusion research and nonproliferation communities. Given the increasing global interest in fusion energy, these measures are critical to ensuring that its development remains secure and aligned with peaceful objectives.