- Design of a metallic fuel core
- ESFR-SMR preliminary design
- Experimental platform under preparation
- Gas bubble measurements
- Fuel
- Creation of an open-access virtual reactor for education and training
- Social aspects of ESFR Technology
- Highlights from the MTLM 2024 Conference
Design of a metallic fuel core
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An extensive review of UK and US experience in metallic fuel was carried out, particularly focused on U-Mo and U-Pu-Zr fuel allow, respectively. Consequently, and due to the successful experience achieved in the US, U-Pu-Zr fuel was selected towards the development of the ESFR with metallic fuel.
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After optimization study, a configuration was selected for the ESFR core with metallic fuel, allowing the Pu content reduction to 13.25%, the pin and assembly dimension reduction (see Fig. 1) as well as leading to a more compact core which provides room for more spent fuel subassemblies storage.
This option (Fig. 2) was selected after the corresponding neutronic evaluation, involving sensitivity calculations to Pu content, characterization of safety-related reactivity coefficients and estimation of equilibrium cycle performance.
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Figure 1 – SA designs of reference ESFR-SMART and the one proposed for ESFR-MET.
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Figure 2 – ESFR-MET radial core map.
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The core maintains the 6-batch operation cycle and the two core regions equivalent to the ESFR-MOX design.
The core does not include fertile regions while the fissile fuel heights are equivalent to the reference ESFR-MOX concept. The achieved core configuration is a breeder reactor, reaching a very limited reactivity swing along the operation cycle (Fig. 3).
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Figure 3 – ESFR-MET cycle-wise core reactivity for 3 consecutive full in-core residence periods.
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An accident analysis task has been started,aiming at extending and benchmarking the models related to the metallic fuel behaviour in transients via the analysis of ULOF and UTOP transient sequences.
A simple one-channel benchmark was carried out to cross-check system code models, involving TRACE, SIM-SFR and ATHLET codes. A good agreement was obtained when comparing selected parameters, such as the radial temperature profile at steady state conditions (Fig. 4) or temperature evolution during transient conditions.
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Figure 4 – Channel model: radial profile evaluated for the axial node with highest power density.
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In the frame of this task, a mobility action has been launched at PSI and supported by the ESFR-SIMPLE EURATOM project, and DOE-NE ART fast reactor program.
The goal was to perform a set of calculations using ANL code SAS4A and thus enabling the next step which involves benchmarking European fuel performance codes applied to metallic fuel (Fig. 5).
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Figure 5 – Left to right: Bo Feng (ANL), Daniele Timpano (PSI) and Nicolas Stauff (ANL) at Argonne National Laboratory.
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ESFR-SMR preliminary design
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To provide an optimized design of the ESFR-SMR core, several steps were adopted. First, an initial ESFR-SMR core design was proposed by downscaling the ESFR-SMART design and applying transportability constrains. Second, a multi-physics optimization of the initial ESFR-SMR core was performed using the SDDS tool.
The optimized parameters included the core power, target discharge burnup, various internal core dimensions, Pu content, number of fuel batches, and reflector materials. Various performance criteria and safety-related constraints were considered in the optimization process This, for example, includes maximizing the total power, minimizing sodium temperature in ULOF, maximizing margins to fuel melting in UCRW, achieving fuel cycle above 300 EFPD, etc.
The outcome of the optimization process are two ESFR-SMR core designs differing by the reflector materials, namely stainless steel (EM10) and MgO. For both cores, the nominal power is about 360 MWth, compared to 3600 MWth of the large ESFR-SMART.
For the system design, a parametrical analysis has been performed to determine the most promising choices of design focusing on the number of primary loops, IHX dimension, FHS system design, etc. Additional important activities include re-designing ESFR-SMR primary circuit components and preparation of the corresponding CAD drawing to be used in the system analysis. The “vademecum” file, containing a comprehensive design data of the ESFR-SMR systems, is under development.
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Figure 6 – Radial layouts of the optimized ESFR-SMR cores
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Experimental platform under preparation
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Firstly, a review of core-catcher designs and associated mitigating devices in the past SFR has been carried out to define additional core-catcher thermo-mechanical performance options that could improve future reactor safety.
This has led to the definition of mitigation measures to protect the core-catcher in the short term and then in the long term. These different measures are then proposed to mitigate the thermal load during both corium jet impingement on the core catcher (short-term) and corium pool cooling (long-term) exposure. These suggested additional mitigation measures will be evaluated in representative experiments and quantified in parallel by modelling analysis (to treat the scaling effects to reactor).
The experimental evaluation of the influence of the proposed mitigation measures on core-catcher ablation by the impact of a corium jet is being carried out in the HANSOLO facility at LEMTA with simulating fluids. The influence of the proposed mitigation measures on long-term ablation process is being studied in the LIVE-CC facility at KIT.
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Figure 7 – Proposition of pods under the corium transfer tube. Left: flat surface, middle: inclined surface, right: concave surface
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Preparation work for HANSOLO experiment
Initial feasibility tests have been carried out, although they are not representative of reactor conditions (water jet flow rate too high). An image of the important ablation obtained this pre-test is displayed in Figure 6.2-3 in the following conditions : ice temperature: -2 °C, jet temperature: 23 °C, jet speed: 24 m/s, nozzle diameter: 6 mm. At present, devices are being set up to orientate the impacting surface of the jet and maintain it during the experiment, in the process of which while visualization shall not be disturbed by the flowing water.
The preparation work is completed, and the calibration of measurement parameters is accomplished. The test campaigns are scheduled to start in September.
Test definition and instrumentation of LIVE- CC tests
LIVE-CC mockup is specially designed for ESFR-Core catcher research. In the current project, a test matrix with 3 test series have been defined: LIVE-CCH (Core-catcher with holes), LIVE-CCS (Core-catcher with salt pods), LIVE-CCM (Core-catcher with metal pods). LIVE-CCH test investigates the long-term healing effect (by corium solidification) of an ablated cavity in the core-catcher bottom plate if the cooling of sodium around the core catcher is available. For each of these LIVE-CC tests, two pods or two holes will be implemented in the test vessel. The geometry of the pods/holes is cylindrical. The diameter of the objects is 80 mm.
A dense array of thermocouples (TCs) has been installed around and inside the pods to capture the temperature field as well as the ablation/heating dynamics. The total number of the additional thermocouples amounts to 90 pieces for each LIVE-CC test. The arrangement of thermocouples is different for each of the two objects in order to obtain a larger range of temperature field.
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Three bellows will be designed in the ESFR-SIMPLE project. They would be implemented in:
- Secondary loops with a pipe diameter of 700 mm,
- Decay heat Removal System (DHR) with a pipe diameter of 250 mm (need of qualification),
- A mock-up at CEA for sodium tests with a diameter of 500 mm.
Different assumptions have been set during the first year of the project:
- Using the usual manufacturing process (with a longitudinal seam weld), despite the NPE requirements
- to develop a component that is able to work below the creep range
- EJMA standard is the most commonly used guideline, so that it has been selected for the next phases of the task (bellows supply is more convenient when using EJMA)
Several components should be tested. The test bench is currently under design and should be able to reproduce the appropriate operating conditions.
The schedule of tasks before the test commissioning is as follows:
- Design the mock-up – mid 2024
- Supply the bellows – mid-end 2024
- Supply the mock-up – mid 2025 (with factory tests)
- Modification of the DOLMEN facility – mid 2025
- Implement the mock-up on DOLMEN facility – end 2025
- Run the sodium tests – beginning 2026
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Tested Mock-up
Imposed Translation displacements in order to simulate the pipe thermal expansion, N number of cycles
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An experimental setup to qualify a novel inductive gas bubble measurement system was constructed. The liquid metal alloy GaInSn is used as a model fluid. The setup consists of a rectangular vessel with the inner cross-section of 50 × 50 mm2 and a height of 300 mm. At the bottom of the column, four orifices can be inserted to generate gas bubbles at different positions.
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Figure 9 – Schematic and (b) photograph of the rectangular column for gas bubble measurements in liquid metal.
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The robust and repeatable generation of bubbles with different sizes is a challenging task, because a careful preparation of different injection needles and a very precise measurement of the bubble diameter is required. Especially, for training of machine learning algorithms, the exact diameter is essential. Therefore, it was decided to model bubbles by artificial non-conducting spheres with defined diameters.
The amplitude of the measured signal directly scales with the size of sphere, which also indicates that bubble size and position can be bijectively reconstructed from the CIBD measurements.
Accompanying to these experiments, a numerical model of the experimental setup was set up, which allows the simulation of the induced signals at the gradiometric coils for a variety of different bubble positions and sizes
Experimental results of the previously developed CIBD method was validated with full bubble reconstructions using the ultrafast ROssendorf Fast Electron beam X-ray tomography system (ROFEX) at HZDR.
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Figure 10 – Functional principle of ROFEX [1]
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Figure 11 – Photograph of the ROFEX detector head
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During fuel fabrication, the aim is to achieve a fuel density of about 95%dth. However, after irradiation, the density near the central hole is very low. At low linear heat rate and high burn-up, the density is also quite low (60-70%dth) due to fission gas retention. The effect of porosity on thermal properties is not well understood, especially for porosities above 5% at high temperatures.
In order to improve our knowledge on this aspect, fuel disks of (U,Pu)O2 with different levels of porosity ranging from 14% to 30% were fabricated at CEA Marcoule (Fig. 1).
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Figure 12: Fuel porous disks fabricated at CEA Marcoule
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A small part of these fuels is currently being characterized at CEA Marcoule (ceramography, optical analysis, μ-Raman, XRD, SEM), see examples of microstructures obtained in Fig. 2.
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Figure 13: Microstructures of the porous fuels fabricated
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The rest of the fuels will soon be transported to the JRC Karlsruhe, where the thermal properties (thermal diffusivity, heat capacity, emissivity, in the temperature range from 500K to 3000K) will be measured, using the Laser Flash and Laser CLASH methods (Fig. 3).
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Figure 14: Laser Flash (left) and Laser CLASH (right)
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These properties will then be modelled using atomistic tools and representative elementary volumes in order to study the effect of the burn-up and the properties involved in the radiative contribution at high temperature. Simulations of the effect of high porosity levels on thermal properties will also be performed.
Finally, the interpretation of both experimental data and simulation results will be carried out in order to establish a new model for the effective thermal conductivity.
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Creation of an open-access virtual reactor for education and training
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The GeN-Foam multiphysics solver has been developed and tested on ESFR-SMART core by simulating nominal power core flowering. GeN-FOAM/OFFBEAT (primary system) and Modelica (secondary system) models were built and coupled for virtual reactor simulations.
Next step is to adapt the ESFR-SIMPLE virtual reactor model based on design updates.
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Figure 15 – Coupled thermo-mechanics and thermal-hydraulics computed geometry deformations of the ESFR-SMART core. Displacements are magnified by a factor 60.
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Social aspects of ESFR Technology
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The goal is to conduct a qualitative study on ESFR-SIMPLE project partners’ and the public’s perceptions and expectations regarding ESFR-SIMPLE SMR technology developments.
All the carried-out activities pertain to the first step of this research: Identifying project partners’ perceptions and expectations about ESFR-SIMPLE SMR technology developments.
Activities carried out
Identifying project partners’ perceptions and expectations about ESFR-SIMPLE SMR technology developments
- Identification of five main narratives associated with SMRs among SMR proponents: 1) Affordable energy generation; 2) Smarter energy generation; 3) Greener energy generation; 4) Safer energy generation; 5) Proliferation resistant energy generation.
- 25 1-hour long interviews were conducted with project partners to collect data about their perceptions and expectations regarding SMRs & the ESFR-SIMPLE SMR. Interviewees included: Advisory board members; WP leaders; WP members; Members of the funding organization.
- Interview transcription and analysis (using the MXQDA software) was completed.
- The previously narratives identified during the literature review were confronted with interview results.
Next steps
- Identifying the public perceptions and expectations about the ESFR-SIMPLE SMR in two contrasted socio-political contexts (France and the UK). 10 interviews planned with civil society members and 2 focus-groups with local communities (one in France and one in the UK)
- Identifying potential frictions points between the public and the project partners’ perceptions and expectations about the ESFR-SIMPLE SMR
- Formulating social, political & ethical recommendations for the use and development of the ESFR-SIMPLE SMR through a cross-case analysis
- Analysing how project partners respond to research findings presented through regular feedback.
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Highlights from the MTLM 2024 Conference
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The Measurement Techniques for Liquid Metals (MTLM) 2024 workshop was an event that brought together researchers and experts from various fields to discuss the latest advancements in Europes sodium fast reactor R&D activities and related fields as liquid metal instrumentation. Here’s a detailed overview of the key highlights from this unforgettable conference.
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An International Participation
With more than 45 participants from 18 institutions spanning 3 continents and 10 countries, MTLM 2024 reaffirmed its status as a premier gathering for specialists in sodium fast reactors. The countries with the highest representation were Germany with 20 participants, followed by France with 11, and the UK with 3. This diverse group of attendees underscored the global commitment to advancing research and innovation in this field.
Technical content
The conference agenda was packed with insightful sessions and contributions, including 7 sessions with 22 contributions from participants sharing their latest research findings and developments, covering various aspects of sodium fast reactors and liquid metal instrumentation e.g., eddy current flow meters, ultrasound based and inductive measurement techniques, X-Ray and neutron imaging. A keynote speech on safety considerations of liquid metal cooled reactors set the tone for the discussions and provided a comprehensive overview of the current state and future prospects of sodium fast reactors.
Hands-On Learning and Lab Visits
One of the standout features of MTLM 2024 was the emphasis on practical learning: Participants had the opportunity to engage in hands-on experiments in HZDRs Magnetohydrodynamics lab and learn about ultrasound Doppler velocimetry, inductive bubble detection and eddy current flow measurements for half a day.
The other half was devoted to lab visits to some of HZDRs large-scale facilities, including:
- ROFEX, an ultrafast X-Ray tomograph to non-invasively investigate highly transient phenomena e.g., two-phase flows, with up 8,000 cross-sectional images per second and a spatial resolution of about 1 mm (https://www.hzdr.de/db/Cms?pOid=30242&pNid=393)
- DRESDYN, the DREsden Sodium facility for DYNamo and thermohydraulic studies, an infrastructure project devoted both to large scale liquid sodium experiments with geo- and astrophysical background, as well as to investigations of various energy related technologies (https://www.hzdr.de/db/Cms?pOid=40412&pNid=3163)
- HZDRs Magnetohydrodynamics Lab with the impressive liquid metal model caster LIMMCAST (https://www.hzdr.de/db/Cms?pOid=25444&pNid=3164), including the liquid metal battery lab.
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