Search Results (143)

A design for a small chloride salt fast reactor (sm-MCFR) is presented through the integration of molten salt reactor and small reactor technologies, targeting efficient transmutation of transuranic (TRU) elements in spent nuclear fuel and rapid reactor deployment. The feasibility exploration and research on the design boundaries of sm-MCFR will be conducted in this article. The core adopts a dual-fluid configuration, in which the fuel salt and coolant circulate independently. Chloride salt is selected as the fuel carrier due to its high solubility for heavy metal nuclides and the low neutron absorption cross-section of chlorine, which help to form a hard fast-neutron spectrum and thereby enhance transmutation efficiency. The cooling system employs a direct supercritical carbon dioxide (s-CO₂) cycle, simplifying the overall layout. For the neutronics design, simulations were carried out using the TMCBurnup (TRITON MODEC Coupled Burnup Code). By adjusting the core geometry, fuel salt composition, and reprocessing strategy, the sm-MCFR achieves a hard fast-neutron spectrum but also demonstrates good potential for fuel utilization. In terms of thermal–hydraulic design, the heat exchange effect of the reactor core can be improved by adjusting the proportion of the coolant and the flow direction. The sm-MCFR is expected to become a promising candidate for advanced small reactors that have potential applications in nuclear waste transmutation and distributed energy generation. Full article

Transient analyses of liquid-fueled molten salt reactors involve strong coupling among neutronics, delayed neutron precursor transport, thermal–hydraulics, and solid heat transfer, leading to high computational costs for repeated high-fidelity simulations. To enable fast multi-physics prediction at unseen operating conditions, a parametric non-intrusive reduced-order model (ROM) combining proper orthogonal decomposition (POD) and higher-order dynamic mode decomposition (HODMD) is developed. Coupled full-order snapshots generated from an OpenFOAM-based one-eighth symmetric core model based on a simplified MSRE benchmark configuration are used to construct reduced representations for 11 physical fields. The POD truncation rank, HODMD delay dimension, and interpolation model are selected using leave-one-out cross-validation, with polynomial, radial basis function, and Gaussian process regression models considered as interpolation candidates. For unseen parameter points, the model maintains high accuracy in both the interpolation stage and the temporal extrapolation stage. In the temporal extrapolation stage, the highest mean relative L₂ error for the inlet-temperature-step case is 2.112%, whereas all mean relative L₂ errors for the inlet-velocity-step case remain below 0.177%. The results indicate that, under the present cases and parameter settings, the proposed framework provides an accurate and rapid surrogate for multi-physics transient prediction. Full article

Reaction-bonded SiC (RBSC) ceramics exhibit limited hydrothermal corrosion resistance due to the presence of residual silicon. This study presents a strategy to enhance the corrosion resistance of RBSC through homogeneous incorporation of MoSi₂ and concurrent reduction in residual silicon content. Three material systems were fabricated via reactive melt infiltration: conventional RBSC with a SiC/C preform (SC), a SiC–MoSi₂ composite incorporating commercial Mo₂C powder via physical mixing (MC), and a SiC–MoSi₂ composite derived from a Mo₂C/C precursor synthesized by a molten salt method (MS). The Mo₂C/C composite synthesized at 1150 °C exhibited fine, uniformly distributed Mo₂C particles coated on carbon black, contrasting with the agglomerated distribution in commercial Mo₂C mixtures. During reactive sintering at 1600 °C, Mo₂C reacted with molten Si to form MoSi₂, reducing residual Si content. Sample MS achieved the lowest residual Si (8.77 ± 0.45 vol.%), followed by MC (12.43 ± 0.86 vol.%) and SC (19.17 ± 1.01 vol.%). All samples achieved near-full densification (open porosity < 0.1%), with bulk densities of 2.96 ± 0.05, 3.03 ± 0.03, and 3.07 ± 0.03 g/cm³ for SC, MC, and MS, respectively. Microstructurally, MS displayed homogeneous MoSi₂ dispersion, while MC showed partial MoSi₂ aggregation, and SC contained continuous residual Si regions. Hydrothermal corrosion tests at 345 °C and 15 MPa for 9 days demonstrated that corrosion resistance followed the order MS > MC > SC. After 9 days, weight loss was 22.3970 ± 1.2059 mg/cm² (SC), 17.6370 ± 0.8266 mg/cm² (MC), and 15.4347 ± 0.7807 mg/cm² (MS), with corrosion depths of 393.17 ± 27.46, 267.40 ± 24.44, and 224.60 ± 25.13 μm, respectively. The enhanced performance of MS arises from two synergistic factors: reduced residual Si minimizes large corrosion pores, while uniform distribution of MoSi₂ facilitates the formation of a stable, dissolution-resistant composite oxide layer composed of MoO₃ and SiO₂, in which MoO₃ restrains excessive dissolution of SiO₂ through a pinning effect. These findings demonstrate that combining residual Si reduction with homogeneous MoSi₂ incorporation via molten salt-synthesized precursors offers an effective strategy for improving hydrothermal corrosion resistance of reaction-bonded SiC-based materials for applications in high-temperature and high-pressure aqueous environments such as nuclear water reactors. Full article

In two-phase systems with heat transfer, developing tools that allow the analysis of interphase phenomena is crucial. In molten salt nuclear reactors, the fuel salt and helium in the core form a two-phase liquid–gas system. Understanding the heat transfer behavior between phases allows us to assess the impact of temperature changes in each phase as well as the feedback of neutron processes in the reactor. This work proposes using an upscaled heat transfer model to analyze the two-phase system, highlighting the importance of solving boundary value problems to obtain the closure variables in a unit cell with symmetry and periodicity. The closure variables are crucial for determining the heat transfer coefficients that exhibit the MSR’s scaled behavior. The coefficients are validated against the literature, and the results of the numerical experiments show that the cross-heat transfer coefficients exhibit symmetric properties. Full article

This review examines current research and development directions in thorium-based nuclear fuel cycles and reactor systems, including innovative and modular reactor concepts being investigated in several nuclear-producing countries. The analysis considers the feasibility of integrating thorium-containing fuels into both existing and emerging reactor technologies. Particular attention is paid to the potential use of thorium-based fuels in pressurized water reactors (PWRs) as transitional platforms that can enable gradual introduction in thorium without requiring immediate deployment of entirely new reactor architectures. This study synthesizes representative quantitative results reported in the recent literature, including neutronic performance metrics, conversion ratio estimates, and fuel behavior characteristics of mixed Th–U oxide fuels under typical operating conditions. These results are evaluated together with broader system-level considerations, such as fuel cycle closure potential, materials performance, and technology readiness across different reactor classes. A comparative assessment of light water reactors (LWRs), heavy water reactors (HWRs), and molten salt reactors (MSRs) demonstrates that each platform offers distinct advantages and limitations for thorium deployment. While LWR systems provide the most realistic near-term pathway for partial thorium introduction within the existing nuclear infrastructure, HWR and MSR concepts offer more favorable conditions for efficient thorium utilization and potential Th–U fuel cycle closure. These reactor classes are currently being explored within national research and development programs focused on advanced and modular nuclear technologies. By integrating neutronic analysis, materials considerations, fuel cycle strategies, and techno-economic factors, this review provides a system-level perspective on the research and development of innovative thorium reactor concepts and outlines realistic pathways for their gradual implementation in evolving nuclear energy systems. Full article

Molten salt electrodeposition is a promising technique to prepare high-performance tungsten coatings for fusion reactor first-wall components. However, the ultra-high temperature during deposition causes severe grain coarsening and precipitate dissolution in CuCrZr alloy substrates, resulting in dramatic mechanical property degradation. In this study, a thermal cycle at 1223.15 K for 100 h was employed to simulate the thermal impact of molten salt tungsten electrodeposition (MSE) on CuCrZr alloys, and an aging treatment (703.15 K for 12 h) was adopted to restore the degraded mechanical properties. After aging, the tensile strength and yield strength recovered to 378.35 ± 7.40 MPa and 261.02 ± 3.40 MPa, meeting the minimum tensile property requirements of ITER for CuCrZr alloys. The recovery is attributed to nano-sized Cr-rich phase precipitation and high-density dislocations, providing effective Orowan precipitation strengthening. This work provides the first simple, engineering-friendly post-treatment to repair performance degradation of CuCrZr under the extreme thermal exposure of molten salt electrodeposition, which is critical for large-scale fabrication of high-performance plasma-facing components (PFCs) for fusion reactors. Full article

As the key technology of space exploration, space power has been a major area of international research focus. A lot of research work has been carried out around the world for the space nuclear reactor using the heat pipe, liquid metal and gas cooling methods. With the development of molten salt reactor in the Generation IV reactor system, molten salt dissolving fissile material and acting as a coolant at the same time has become a new cooling scheme, which provides new ideas for the design of space nuclear reactors. In this study, a novel reactor, the liquid-solid dual-fuel space nuclear reactor (LSSNR) was preliminarily proposed, combining the molten salt fuel and cross-shaped spiral solid fuel to achieve the design goals of 30-year lifetime and an active core weight of less than 200 kg. Monte Carlo neutron transport code OpenMC based on ENDF/B-VII.1 library was employed for neutronics design in the aspect of fuel type, cladding material, reflector material and the spectral shift absorber. Then, the thickness of the control drum absorber was optimized to meet the requirement of the sufficient shutdown margin, lower solid fuel enrichment, and 30-effective-full power-years (EFPY) operation lifetime. Finally, UC solid fuel with U-235 enrichment of 80.98 wt.% and B₄C thickness of 0.75 cm were adopted in LSSNR, and BeO was adopted as the reflector and the matrix material of the control drum. A spectral shift absorber Gd₂O₃ was used to avoid the subcritical LSSNR returning to criticality in a launch accident. The k_eff with the control drum in the innermost position is 0.954949, and the k_eff reaches 1.00592 after 30 EFPY of operation. The total mass of the active core is 158.11 kg. In addition, the thermal-hydraulic feasibility of LSSNR using cross-shaped spiral fuel was analyzed based on a 4/61 reactor core model. The structure of cross-shaped spiral fuel achieves enhanced heat transfer by generating turbulence, which leads to a uniform temperature distribution of the coolant flow field and reduces local temperature peaks. Based on the LSSNR scheme, some neutronic characteristics were analyzed. Results demonstrate that the LSSNR has strongly negative reactivity coefficients due to the thermal expansion of liquid fuel, and the fission gas-induced pressure meets safety requirements. One hundred years after the end of core life, the total radioactivity of reactor core is reduced by 99% and is 7.1305 Ci. Full article

This study provides the first systematic verification of the CUPID-MSR thermal–hydraulic code for molten-salt reactor applications, incorporating temperature-dependent thermophysical properties of two chloride-based molten salts, KCl–UCl₃ and NaCl–MgCl₂–TRUCl₃. Verification against the de Vahl Davis benchmark for Rayleigh numbers ${10}^3$–${10}^6$ shows agreement within 0.4–3.9%, with the simulations accurately reproducing the reference Nusselt numbers, velocity fields, and thermal boundary layers. Additional temperature sensitivity studies confirm stable and accurate predictions using the implemented thermophysical property correlations over a broad temperature range. Furthermore, the applicability of the Boussinesq approximation is assessed by comparing the full variable-density formulation with the Boussinesq formulation, revealing that the approximation remains accurate when the relative density variation is below approximately 10% ($\beta \Delta T\lesssim 0.1$). The obtained threshold is consistent with classical Boussinesq criteria and confirms their relevance for molten-salt flows. Full article

This study investigates the core optimization of a Prismatic Solid Molten-Salt Reactor (PSMSR) to meet key objectives of compactness, high power density, and extended operational life. With graphite irradiation resistance being a paramount concern in high-flux environments, the analysis focuses on the influence of core height-to-diameter ratio, active zone size, and reflector thickness on the graphite displacement per atom (DPA) distribution and burnup performance. The results indicate an optimal active core configuration characterized by a 1:1 height-to-diameter ratio, a 175 cm active zone radius, and a 55 cm reflector. Building on these findings, reactivity-control strategies were refined. An evaluation of burnable-poison addition against fuel-loading optimization revealed that the latter, by adjusting the TRISO (TRi-structural ISOtropic) packing factor and control-rod dimensions, can meet the safety shutdown margin requirements and substantially improve the fuel utilization efficiency, ultimately achieving a burnup depth of 50.3 MWd/kgU and a 10-year operation lifetime without refueling at a 500 MWt power level. This research provides an effective technical solution for the modular deployment of solid-state molten-salt reactors in remote areas and in special application scenarios. This research offers a viable technical pathway for implementing solid-fueled molten-salt reactors in remote and specialized scenarios, enabling their modular deployment. Full article

Advanced high-temperature fluid reactors (ARs), such as sodium fast reactors (SFRs) and molten salt cooled reactors (MSCRs) utilize high-temperature fluids at ambient pressure. To melt the fluid during reactor startup and prevent fluid freezing during cooldown, the thermal–hydraulic systems of such ARs include heater zones consisting of specific heaters with controllers, temperature sensors, and thermal insulation. The failure of heater zones due to insulation material degradation or improper installation, resulting in parasitic heat losses, can lead to fluid freezing. The detection of faults using a heat-transfer model is difficult because of a lack of knowledge of the experimental details. Data-driven machine learning of heater zone temperature time series offers a viable alternative. In this study, we benchmarked the performance of recurrent neural networks (RNNs) in an analysis of heat-up transient temperature time series of heater zones installed on a liquid sodium vessel. The RNN models include long short-term memory (LSTM) and gated recurrent unit (GRU) networks, as well as their bi-directional variants, BiLSTM and BiGRU. Anomalous temperature points were designated using a percentile-based threshold applied to residual fluctuations in the detrended temperature time series. Additionally, the impact of the exponentially weighted moving average (EWMA) method on detection accuracy was examined. The RNN models’ performance was assessed using precision, recall, and F₁ score metrics. Results demonstrated that RNN models effectively detect anomalies in temperature time series with the best models for each heater zone achieving F₁ scores of over 93%. To explain the variations in RNN model performance across different heater zones, we used Kullback–Leibler (KL) divergence to quantify the relative entropy between training and testing data, and the Detrended Fluctuation Analysis (DFA) to assess long-range temporal correlations. For datasets with strong long-range correlations and minimal relative entropy between training and testing data, GRU is the best-performing model. When the data exhibits weaker long-term correlations and a significant relative entropy between training and testing distributions, BiGRU shows the best performance. For the data sets with intermediate values of both KL divergence and DFA, the best performance is obtained with LSTM and BiLSTM, respectively. Full article

Iodine is produced through nuclear fission reactions in nuclear reactors. Understanding the electrochemistry of iodine species is crucial for reprocessing used nuclear fuels via molten salt electrolysis, deploying next-generation molten salt nuclear reactors, and developing iodide-based molten salt batteries. Cyclic voltammetry (CV) was conducted in LiCl-KCl eutectic molten salts at 450, 500, and 550 °C, both with and without the addition of KI as an iodine source. Based on the CV results, the diffusivities of iodide and triiodide species, as well as the activation energies for diffusion, were determined. Additionally, formal potentials of various iodide and interhalogen complexes were derived, allowing for the calculation of the stability constants for halide exchange reactions. The diffusivities of iodide ranged from 0.14 to 6.9 × 10⁻⁷ cm²/s, while those of triiodide were roughly an order of magnitude lower. Increasing the KI content from 1 wt% to 5 wt% reduced the diffusion coefficient, whereas increasing temperature, as expected, boosted diffusivity. The activation energy for iodide diffusion in LiCl-KCl increased from 46.5 kJ/mol to 112 kJ/mol as KI concentration rose from 1 wt% to 5 wt%. Full article

The transition toward carbon-neutral energy systems has revived interest in nuclear technologies, particularly small and micro modular reactors (SMRs and MMRs) as flexible, safe and efficient alternatives to conventional large-scale power plans. In the Czech Republic, Centrum výzkumu Řez (CVŘ) is developing Energy Well (EW), a molten salt-cooled micro modular reactor concept employing FLiBe (Fluoride Lithium Beryllium) as primary and secondary coolant and a supercritical CO₂ (sCO₂) tertiary loop. A dedicated experimental facility was built to reproduce EW operating conditions and provide critical data on thermohydraulic behavior, fuel properties and heat-transfer mechanisms. This paper presents the development and assessment of a TRACE (TRAC/RELAP Advanced Computational Engine) model of the experimental facility, including specific methodologies for the main heater and the heat exchanger. Model accuracy was assessed through comparison with experimental commissioning data. The simulations demonstrated overall model consistency, especially regarding the heat exchanger and the main heater general performances, while some discrepancies were observed inside the main heater graphitic core. Other discrepancies were observed along the loop, mainly resulting from modeling simplifications and lack of information regarding certain experimental loop phenomena. In particular, the pressure calculation showed large inconsistencies mainly connected to the complexity of pressure measurements in molten salt circuits and the lack of specific head loss correlations. This study also helped identify broader issues in both the code (persistent error in generating CO₂ property tables and instabilities resulting from FLiBe interactions with non-condensable gases) and the experimental loop (defect in the heat exchanger filling and uncertainties on sensors location), also contributing to resolving sensor-related inconsistencies in the facility. Results confirm TRACE as a reliable tool for modeling molten salt systems, regarding the temperature distribution and the heat transfer. However, depending on the specific experimental case, this paper introduces specific limitations, such as some inconsistencies in the pressure drops distribution, in order to support the future development of TRACE code. Beyond technical advances, this work provides unique experimental data and fosters international collaboration in advancing SMR and molten salt reactor technologies. Full article

Molten Salt Reactors (MSRs) offer significant advantages over conventional reactors but introduce unique modeling challenges due to their circulating liquid fuel and strong coupling among nuclear, chemical, and fluid transport processes. These challenges are amplified in depletion calculations, where MSR specific phenomena such as online refueling, off-gas removal, material redistribution, and other flow driven processes must be accurately represented. This work presents a novel multi-point depletion model that efficiently and accurately predicts isotopic evolution in MSRs by explicitly accounting for these characteristics. The mathematical formulation is derived from first principles and is computationally implemented in the open-source depletion code ONIX using neutronics solutions from open-source transport code OpenMC. The new model represents the entire primary loop by dividing it into interconnected depletion zones and tracks nuclide transport, irradiation, and removal mechanisms through a system of coupled ordinary differential equations. This approach enables parallel computation and improves performance over traditional sequential depletion methods. Validation of the developed model against Molten Salt Reactor Experiment data shows good agreement for salt-seeking isotopes and those without noble gas precursors, while discrepancies for other nuclides suggest underestimation of the corresponding removal rates. The depletion model was further applied to a reference Molten Salt Fast Reactor design to assess a new reprocessing scheme intended to expedite the achievement of equilibrium operation. Full article

Molten salts act as fuel carriers and coolants in liquid-fueled molten salt reactors (MSRs), characterized by strong coupling between neutronics and thermal hydraulics (N-TH) in practical MSR operations. In this study, an in-house light water reactor static and transient analysis code, RESTA-3D, has been extended and applied to MSR transient safety analysis. A parallel multi-channel TH model and a neutron kinetics model incorporating the transport of delayed neutron precursors were implemented into RESTA-3D to account for the MSR-specific N-TH coupling characteristics. Few-group cross-section parameters were generated by the TMSR-LINK code and tabulated for use in RESTA-3D to support MSR transient analysis. The code system was verified against simulation results from well-established MSR dynamics codes and validated against experimental data from the MSRE (Molten Salt Reactor Experiment), covering steady-state temperature distributions, fuel pump-driven transients, and the MSRE natural convection test. Good agreement of the improved RESTA-3D results with the experiment data of MSRE was confirmed, with key parameters such as temperature within a 1% deviation margin, thereby confirming that RESTA-3D is suitable for MSR dynamics analysis. Furthermore, this code was applied to assess the transient characteristics of a 2 MWth thorium-based molten salt reactor (TMSR). The core characteristics, including the inlet fuel overcooling and overheating, unprotected fuel pump start-up and coast-down, were simulated and discussed, indicating that the 2 MWth TMSR design possesses high inherent safety. Full article

Targeted radionuclide therapy (TRT) is an innovative and flexible approach for treating various forms of cancer, enabling selective delivery of cytotoxic radiation to cancerous cells while minimizing damage to healthy tissue. Although TRT has proven to be highly promising for treating even advanced-stage cancers, ensuring a stable supply of the radionuclides essential for its use remains a significant challenge today. This is also true for radionuclides utilized in nuclear imaging procedures, such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT). Liquid-fueled molten salt reactors (MSRs) are promising for producing large quantities of highly desirable radionuclides for imaging and therapy, offering the ability to recover these radionuclides online without the need for interruptions to power production. In this study, the production of numerous beta- and alpha-emitting radionuclides for use in TRT and diagnostic procedures was studied in two small, geometrically identical, thermal spectrum MSR models—one operating with LEU fuel, and the other with a mixture of HALEU and thorium—using a novel MSR refueling and waste management concept. For therapeutic alpha emitters such as ²²⁵Ac and ²¹³Bi, the impact of thorium utilization on production yields was significant, facilitating greatly increased production. Full article