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Keywords = supercritical water reactor

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20 pages, 1338 KiB  
Article
Two-Dimensional Fuel Assembly Study for a Supercritical Water-Cooled Small Modular Reactor
by Valerio Giusti
J. Nucl. Eng. 2025, 6(3), 26; https://doi.org/10.3390/jne6030026 - 9 Jul 2025
Viewed by 193
Abstract
Burnable poisoning and fuel enrichment zoning are two techniques often combined in order to optimize the fuel assembly behavior during the burnup cycle. In the present work, these two techniques will be applied to the 2D optimization of the fuel assembly conceptual design [...] Read more.
Burnable poisoning and fuel enrichment zoning are two techniques often combined in order to optimize the fuel assembly behavior during the burnup cycle. In the present work, these two techniques will be applied to the 2D optimization of the fuel assembly conceptual design for the supercritical water-cooled reactor developed in the framework of the Joint European Canadian Chinese development of Small Modular Reactor Technology project, funded within the Euratom Research and Training programme 2019–2020. The initial configuration of the fuel assembly does not include any burnable absorbers and uses a homogeneous fuel enrichment of 7.5% in 235U. The infinite multiplication factor, k, starts from approximately 1.32 and drops, almost linearly, to 1.0 after a burnup of 40.0 MWd·kg−1. The uniform enrichment is, however, responsible for a pin-power peaking factor that with fresh fuel starts from 1.32 and reduces to 1.08 at the end of the burnup cycle. A simplified analytical model is developed to assess the effect of different lumped burnable absorbers on the time dependence of the assembly k. It is shown that using an adequate number of B4C rods, positioned in the outer wall of the fuel assembly, together with a suitable distribution of six different 235U enrichments, it allows for obtaining an assembly k factor that starts from 1.11 at the beginning of the cycle and remains quite constant over a large fraction of the burnup cycle. Moreover, the pin-power peaking factor is reduced to 1.03 at the beginning of the cycle and remains almost unchanged until the end of the burnup cycle. Full article
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35 pages, 1686 KiB  
Review
State-of-the-Art Decarbonization in Sludge Thermal Treatments for Electrical Power Generation Considering Sensors and the Application of Artificial Intelligence
by Rafael Ninno Muniz, William Gouvêa Buratto, Rodolfo Cardoso, Carlos Frederico de Oliveira Barros, Ademir Nied and Gabriel Villarrubia Gonzalez
Water 2025, 17(13), 1946; https://doi.org/10.3390/w17131946 - 29 Jun 2025
Viewed by 564
Abstract
This study explores innovative strategies for decarbonizing sludge thermal treatments used in electrical power generation, with a focus on integrating sensor technologies and artificial intelligence. Sludge, a carbon-intensive byproduct of wastewater treatment, presents both environmental challenges and opportunities for energy recovery. The paper [...] Read more.
This study explores innovative strategies for decarbonizing sludge thermal treatments used in electrical power generation, with a focus on integrating sensor technologies and artificial intelligence. Sludge, a carbon-intensive byproduct of wastewater treatment, presents both environmental challenges and opportunities for energy recovery. The paper provides a comprehensive analysis of thermal processes such as pyrolysis, gasification, co-combustion, and emerging methods, including hydrothermal carbonization and supercritical water gasification. It evaluates their carbon mitigation potential, energy efficiency, and economic feasibility, emphasizing the importance of catalyst selection, carbon dioxide capture techniques, and reactor optimization. The role of real-time monitoring via sensors and predictive modeling through artificial intelligence (AI) is highlighted as critical for enhancing process control and sustainability. Case studies and recent advances are discussed to outline future pathways for integrating thermal treatment with circular economy principles. This work contributes to sustainable waste-to-energy practices, supporting global decarbonization efforts and advancing the energy transition. Full article
(This article belongs to the Section Wastewater Treatment and Reuse)
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17 pages, 1481 KiB  
Article
Radiolysis of Sub- and Supercritical Water Induced by 10B(n,α)7Li Recoil Nuclei at 300–500 °C and 25 MPa
by Md Shakhawat Hossen Bhuiyan, Jintana Meesungnoen and Jean-Paul Jay-Gerin
J. Nucl. Eng. 2025, 6(2), 17; https://doi.org/10.3390/jne6020017 - 9 Jun 2025
Viewed by 488
Abstract
(1) Background: Generation IV supercritical water-cooled reactors (SCWRs), including small modular reactor (SCW-SMR) variants, are pivotal in nuclear technology. Operating at 300–500 °C and 25 MPa, these reactors require detailed understanding of radiation chemistry and transient species to optimize water chemistry, reduce corrosion, [...] Read more.
(1) Background: Generation IV supercritical water-cooled reactors (SCWRs), including small modular reactor (SCW-SMR) variants, are pivotal in nuclear technology. Operating at 300–500 °C and 25 MPa, these reactors require detailed understanding of radiation chemistry and transient species to optimize water chemistry, reduce corrosion, and enhance safety. Boron, widely used as a neutron absorber, plays a significant role in reactor performance and safety. This study focuses on the yields of radiolytic species in subcritical and supercritical water exposed to 4He and 7Li recoil ions from the 10B(n,α)7Li fission reaction in SCWR/SCW-SMR environments. (2) Methods: We use Monte Carlo track chemistry simulations to calculate yields (G values) of primary radicals (eaq, H, and OH) and molecular species (H2 and H2O2) from water radiolysis by α-particles and Li3⁺ recoils across 1 picosecond to 0.1 millisecond timescales. (3) Results: Simulations show substantially lower radical yields, notably eaq and OH, alongside higher molecular product yields compared to low linear energy transfer (LET) radiation, underscoring the high-LET nature of 10B(n,α)7Li recoil nuclei. Key changes include elevated G(OH) and G(H2), and a decrease in G(H), primarily driven during the homogeneous chemical stage of radiolysis by the reaction H + H2O → OH + H2. This reaction significantly contributes to H2 production, potentially reducing the need for added hydrogen in coolant water to mitigate oxidizing species. In supercritical conditions, low G(H₂O₂) suggests that H2O2 is unlikely to be a major contributor to material oxidation. (4) Conclusions: The 10B(n,α)7Li reaction’s yield estimates could significantly impact coolant chemistry strategies in SCWRs and SCW-SMRs. Understanding radiolytic behavior in these conditions aids in refining reactor models and coolant chemistry to minimize corrosion and radiolytic damage. Future experiments are needed to validate these predictions. Full article
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21 pages, 6358 KiB  
Article
Experimental Study and Performance Analysis of a Recuperative Supercritical CO2 Brayton Cycle
by Shucheng Zhang, Juntao Ke, Min Liu, Pingjian Ming and Guopeng Yu
Energies 2025, 18(11), 2986; https://doi.org/10.3390/en18112986 - 5 Jun 2025
Viewed by 401
Abstract
To investigate the operational characteristics of the supercritical carbon dioxide (S-CO2) Brayton cycle and enhance its applicability in practical operating conditions for micro-scale reactors, an experimental platform for a recuperative S-CO2 Brayton cycle is constructed and investigated. Several controllable operational [...] Read more.
To investigate the operational characteristics of the supercritical carbon dioxide (S-CO2) Brayton cycle and enhance its applicability in practical operating conditions for micro-scale reactors, an experimental platform for a recuperative S-CO2 Brayton cycle is constructed and investigated. Several controllable operational parameters, including compressor pump frequency, expansion valve opening, and electric heating power, each intrinsically linked to the thermal characteristics of its corresponding equipment, as well as the cooling water flow rate, are systematically adjusted and analyzed. Experimental results demonstrate that the cooling water flow rate has a significantly greater impact on the temperature and pressure of the cycle system compared to other operational parameters. Based on these findings, steady-state experiments are conducted within a pressure range of 8 MPa to 15 MPa and a temperature range of 70 °C to 150 °C. It is observed that the heat exchange capacity of the recuperator decreases as the cooling water flow rate is reduced, suggesting that sufficient cooling efficiency is required to maximize the recuperative function. Under the condition of a maximum system temperature of 150 °C, the isentropic efficiency of the expansion valve decreases with an increase in the inlet pressure of the valve. However, the overall thermal efficiency of the cycle system requires further calculation and assessment following the optimization of the experimental platform. The result of validation of experimental results is less than 20%. The findings presented in this study offer essential data that encompass the potential operational conditions of the CO2 Brayton cycle section applicable to small-scale reactors, thereby providing a valuable reference for the design and operation of practical cycle systems. Full article
(This article belongs to the Special Issue Supercritical CO2 Power Cycles)
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30 pages, 5789 KiB  
Article
Fischer–Tropsch Biofuel Production from Supercritical Water Gasification of Lignocellulosic Biomass: Process Modelling and Life-Cycle Assessment
by Dimitrios Katsourinis, Dimitrios Giannopoulos and Maria Founti
Processes 2025, 13(3), 895; https://doi.org/10.3390/pr13030895 - 18 Mar 2025
Cited by 1 | Viewed by 669
Abstract
The production of Fischer–Tropsch liquid biofuels from the supercritical water gasification (SCWG) of lignocellulosic biomass is energetically and environmentally assessed by coupling process modelling with Life-Cycle Assessment. A conceptual process model has been developed comprising the following stages: (a) the thermochemical conversion of [...] Read more.
The production of Fischer–Tropsch liquid biofuels from the supercritical water gasification (SCWG) of lignocellulosic biomass is energetically and environmentally assessed by coupling process modelling with Life-Cycle Assessment. A conceptual process model has been developed comprising the following stages: (a) the thermochemical conversion of lignocellulosic biomass in a supercritical water gasification (SCWG) reactor, (b) syngas upgrade through dry reforming (DRR), (c) liquid biofuel production from Fischer–Tropsch synthesis (FTS) and (d) FT product upgrade and refinement, so that diesel-like (FT—Diesel), gasoline-like (FT—Gasoline), and jet fuel-like (FT Jet Fuel) yields are predicted. Parametric studies have been performed, highlighting the effect of biomass concentration and SCWG temperature on end-product yields. Furthermore, alternative scenarios have been examined with respect to: (a) maximizing FT liquid biofuel yields and (b) minimizing heat requirements to potentially achieve a thermally self-sustained process. The results of the simulated process, including liquid biofuel yield and heat-demand predictions, are used as inputs in the inventories compiled for the Life-Cycle Assessment of the overall process. Agricultural and feedstock transportation stages have also been considered. Energetic and environmental benefits and challenges are highlighted through the quantification of Global Warming Potential (GWP), while special importance is assigned to following the REDII sustainability methodology and reference data. Full article
(This article belongs to the Special Issue Processes in Biofuel Production and Biomass Valorization)
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29 pages, 964 KiB  
Review
The Gasification of Marine and Coastal Resources for Syngas Production: A Review
by Gwendal Vonk, Virginie Boy, Jean-Louis Lanoisellé and Thomas Lendormi
Energies 2025, 18(3), 616; https://doi.org/10.3390/en18030616 - 29 Jan 2025
Viewed by 941
Abstract
Coasts are home to one-third of the human population. In the process of energy transition, local biomass and waste resources represent a renewable fuel that can substitute fossil fuels in order to reduce greenhouse gas emissions, hence including marine resources as part of [...] Read more.
Coasts are home to one-third of the human population. In the process of energy transition, local biomass and waste resources represent a renewable fuel that can substitute fossil fuels in order to reduce greenhouse gas emissions, hence including marine resources as part of the eligible feedstock for renewable energy production. Gasification regroups different technologies that aim to convert a solid fuel into a useful gas, and has several applications, such as heat production, power generation, and chemical synthesis. Gasification technologies regroup the traditional “dry” processes that use relatively dry fuels, but recent developments have been made with “wet” processes such as hydrothermal gasification, in sub- or supercritical conditions for the water, which can accept wet fuel. This review focuses on scientific articles that performed gasification of marine resources in order to produce a syngas. First, a definition of marine resources is made, followed by the presentation of marine resources studied in the literature. Secondly, this review presents the different types of gasification reactors and their operating conditions, followed by a summary of the different syngas produced with their composition as a performance indicator. Finally, this review exposes the limitations of the current literature and concludes with perspective propositions. Full article
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18 pages, 3748 KiB  
Article
An Investigation of the Catalytic Activity of Inconel and Stainless Steel Powders in Reforming Primary Syngas
by Claudia Bezerra Silva, Michael Lugo-Pimentel, Carlos M. Ceballos and Jean-Michel Lavoie
Sustainability 2025, 17(3), 980; https://doi.org/10.3390/su17030980 - 25 Jan 2025
Viewed by 1250
Abstract
Biomass is perhaps the only renewable resource on the planet capable of delivering molecules similar to those derived from petroleum, and one of the most developed technologies to achieve this is gasification. When it comes to biomass conversion into fuels and commodities, supercritical [...] Read more.
Biomass is perhaps the only renewable resource on the planet capable of delivering molecules similar to those derived from petroleum, and one of the most developed technologies to achieve this is gasification. When it comes to biomass conversion into fuels and commodities, supercritical water gasification (SCWG) could offer promising solution for producing hydrogen-rich syngas. However, the presence of methane (CH4) and carbon dioxide (CO2) in the syngas could negatively impact downstream processes, particularly when carbon monoxide is also required. Hence, improving the quality of the syngas produced from biomass gasification is essential for promoting the sustainability of several industrial processes. In this context, understanding the principles of the dry reforming of methane (DRM) becomes essential for upgrading syngas with high CH4 and CO2 content, especially when the carbon monoxide content is low. In addition to the experimental conditions used in such process, it has been reported that the material composition of the reactor can impact on reforming performance. Hence, this work aims at comparing the catalytic efficacy of Inconel and stainless steel for reforming syngas derived from SCWG under standard DRM conditions. In this specific work, the metals were directly used as catalyst and results showed that when using Inconel powder, CH4 conversion increased from 3.03% to 37.67% while CO2 conversion went from 23.16% to 51.48% when compared to stainless steel. Elemental and structural analyses revealed that the Inconel’s superior performance might be due to its high nickel content and the formation of active oxide compounds, such as FeNiO, FeCrO3, Fe3O4, Cr2O3, and Cr2NiO4, during the reaction. In contrast, Fe3O4 was the only oxide found in stainless steel post-reaction. Additionally, increasing the total gas feed flow rate was shown to reduce CH4 and CO2 conversions, supporting the known impact of residency time on catalytic efficiency. Full article
(This article belongs to the Section Energy Sustainability)
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13 pages, 700 KiB  
Review
Evaluating Nuclear Forensic Signatures for Advanced Reactor Deployment: A Research Priority Assessment
by Megan N. Schiferl, Jeffrey R. McLachlan, Appie A. Peterson, Naomi E. Marks and Rebecca J. Abergel
J. Nucl. Eng. 2024, 5(4), 518-530; https://doi.org/10.3390/jne5040032 - 15 Nov 2024
Viewed by 1962
Abstract
The development and deployment of a new generation of nuclear reactors necessitates a thorough evaluation of techniques used to characterize nuclear materials for nuclear forensic applications. Advanced fuels proposed for use in these reactors present both challenges and opportunities for the nuclear forensic [...] Read more.
The development and deployment of a new generation of nuclear reactors necessitates a thorough evaluation of techniques used to characterize nuclear materials for nuclear forensic applications. Advanced fuels proposed for use in these reactors present both challenges and opportunities for the nuclear forensic field. Many efforts in pre-detonation nuclear forensics are currently focused on the analysis of uranium oxides, uranium ore concentrates, and fuel pellets since these materials have historically been found outside of regulatory control. The increasing use of TRISO particles, metal fuels, molten fuel salts, and novel ceramic fuels will require an expansion of the current nuclear forensic suite of signatures to accommodate the different physical dimensions, chemical compositions, and material properties of these advanced fuel forms. In this work, a semi-quantitative priority scoring system is introduced to identify the order in which the nuclear forensics community should pursue research and development on material signatures for advanced reactor designs. This scoring system was applied to propose the following priority ranking of six major advanced reactor categories: (1) molten salt reactor (MSR), (2) liquid metal-cooled reactor (LMR), (3) very-high-temperature reactor (VHTR), (4) fluoride-salt-cooled high-temperature reactor (FHR), (5) gas-cooled fast reactor (GFR), and (6) supercritical water-cooled reactor (SWCR). Full article
(This article belongs to the Special Issue Nuclear Security and Nonproliferation Research and Development)
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23 pages, 11306 KiB  
Article
Effect of the Reactor Material on the Reforming of Primary Syngas
by Claudia Bezerra Silva, Michael Lugo-Pimentel, Carlos M. Ceballos and Jean-Michel Lavoie
Molecules 2024, 29(21), 5126; https://doi.org/10.3390/molecules29215126 - 30 Oct 2024
Cited by 2 | Viewed by 1514
Abstract
Syngas, mostly hydrogen and carbon monoxide, has traditionally been produced from coal and natural gas, with biomass gasification later emerging as a renewable process. It is widely used in fuel synthesis through the Fischer–Tropsch (FT) process, where the H2/CO ratio is [...] Read more.
Syngas, mostly hydrogen and carbon monoxide, has traditionally been produced from coal and natural gas, with biomass gasification later emerging as a renewable process. It is widely used in fuel synthesis through the Fischer–Tropsch (FT) process, where the H2/CO ratio is crucial in determining product efficiency and quality. In this sense, this study aimed to reform an emulated syngas resulting from the supercritical water gasification of biomass, tailoring it to meet the H2/CO ratio required for FT synthesis. Conditions resembling dry reforming were applied, using temperatures from 600 to 950 °C and steel wool as a catalyst. Additionally, the effects of Inconel and stainless steel as reactor materials on syngas reforming were investigated. When Inconel was used, H2/CO ratios ranged between 1.04 and 1.84 with steel wool and 1.28 and 1.67 without. When comparing reactions without steel wool performed either in the Inconel or the stainless steel reactors, those using Inconel consistently outperformed the stainless steel ones, achieving CH4 and CO2 conversions up to 95% and 76%, respectively, versus 0% and 39% with stainless steel. It was concluded that the Inconel reactor exhibited catalytic properties due to its high nickel content and specific oxides. Full article
(This article belongs to the Section Applied Chemistry)
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19 pages, 4665 KiB  
Review
A Review of Catalyst Integration in Hydrothermal Gasification
by Emmanuel Galiwango, James Butler and Samira Lotfi
Fuels 2024, 5(3), 375-393; https://doi.org/10.3390/fuels5030022 - 23 Aug 2024
Cited by 2 | Viewed by 1795
Abstract
Industrial scale-up of hydrothermal supercritical water gasification process requires catalytic integration to reduce the high operational temperatures and pressures to enhance controlled chemical reaction pathways, product yields, and overall process economics. There is greater literature disparity in consensus on what is the best [...] Read more.
Industrial scale-up of hydrothermal supercritical water gasification process requires catalytic integration to reduce the high operational temperatures and pressures to enhance controlled chemical reaction pathways, product yields, and overall process economics. There is greater literature disparity in consensus on what is the best catalyst and reactor design for hydrothermal gasification. This arises from the limited research on catalysis in continuous flow hydrothermal systems and rudimentary lab-scale experimentation on simple biomasses. This review summarizes the literature status of catalytic hydrothermal processing, especially for continuous gasification and in situ catalyst handling. The rationale for using low and high temperatures during catalytic hydrothermal processing is highlighted. The role of homogeneous and heterogeneous catalysts in hydrothermal gasification is presented. In addition, the rationale behind certain designs and component selection for catalytic investigations in continuous hydrothermal conversion is highlighted. Furthermore, the effect of different classes of catalysts on the reactor and reactions are elaborated. Overall, design and infrastructural challenges such as plugging, corrosion, agglomeration of the catalysts, catalyst metal leaching, and practical assessment of catalyst integration towards enhancement of process economics still present open questions. Therefore, strategies for catalytic configuration in continuous hydrothermal process must be evaluated on a system-by-system basis depending on the feedstock and experimental goals. Full article
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15 pages, 1277 KiB  
Article
Fast-Neutron Radiolysis of Sub- and Supercritical Water at 300–600 °C and 25 MPa: A Monte Carlo Track Chemistry Simulation Study
by Md Shakhawat Hossen Bhuiyan, Jintana Meesungnoen, Abida Sultana and Jean-Paul Jay-Gerin
Appl. Sci. 2024, 14(16), 7024; https://doi.org/10.3390/app14167024 - 10 Aug 2024
Cited by 1 | Viewed by 1351
Abstract
(1) Background: Supercritical water-cooled reactors (SCWRs) and their smaller modular variants (SMRs) are part of the ‘Generation IV International Forum’ (GIF) on advanced nuclear energy systems. These reactors operate beyond the critical point of water (tc = 373.95 °C and P [...] Read more.
(1) Background: Supercritical water-cooled reactors (SCWRs) and their smaller modular variants (SMRs) are part of the ‘Generation IV International Forum’ (GIF) on advanced nuclear energy systems. These reactors operate beyond the critical point of water (tc = 373.95 °C and Pc = 22.06 MPa), which introduces specific technical challenges that need to be addressed. The primary concerns involve the effects of intense radiation fields—including fast neutrons, recoil protons/oxygen ions, and γ rays—on the chemistry of the coolant fluid and the integrity of construction materials. (2) Methods: This study employs Monte Carlo simulations of radiation track chemistry to investigate the yields of radiolytic species in SCWRs/SMRs exposed to 2 MeV neutrons. In our calculations, only the contributions from the first three recoil protons with initial energies of 1.264, 0.465, and 0.171 MeV were considered. Our analysis was conducted at both subcritical (300 and 350 °C) and supercritical temperatures (400–600 °C), maintaining a constant pressure of 25 MPa. (3) Results: Our simulations provide insights into the radiolytic formation of chemical species such as eaq, H, H2, OH, and H2O2 from ~1 ps to 1 ms. Compared to data from radiation with low linear energy transfer (LET), the G(eaq) and G(OH) values obtained for fast neutrons show a similar temporal dependence but with smaller amplitude—a result demonstrating the high LET nature of fast neutrons. A notable outcome of our simulations is the marked increase in G(OH) and G(H2), coupled with a corresponding reduction in G(H), observed during the homogeneous chemical stage of radiolysis. This evolution is attributed to the oxidation of water by the H atom according to the reaction H + H2O → OH + H2. This reaction acts as a significant source of H2, potentially reducing the need to add extra hydrogen to the reactor’s coolant water to suppress the net radiolytic production of oxidizing species. Unlike in subcritical water, our simulations also indicate that G(H2O2) remains very low in low-density SCW throughout the interval from ~1 ps to 1 ms, suggesting that H2O2 is less likely to contribute to oxidative stress under these conditions. (4) Conclusions: The results of this study could significantly impact water-chemistry management in the proposed SCWRs and SCW-SMRs, which is crucial for assessing and mitigating the corrosion risks to reactor materials, especially for long-term operation. Full article
(This article belongs to the Section Chemical and Molecular Sciences)
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36 pages, 6799 KiB  
Review
The Irradiation Effects in Ferritic, Ferritic–Martensitic and Austenitic Oxide Dispersion Strengthened Alloys: A Review
by Natália Luptáková, Jiří Svoboda, Denisa Bártková, Adam Weiser and Antonín Dlouhý
Materials 2024, 17(14), 3409; https://doi.org/10.3390/ma17143409 - 10 Jul 2024
Cited by 4 | Viewed by 2756
Abstract
High-performance structural materials (HPSMs) are needed for the successful and safe design of fission and fusion reactors. Their operation is associated with unprecedented fluxes of high-energy neutrons and thermomechanical loadings. In fission reactors, HPSMs are used, e.g., for fuel claddings, core internal structural [...] Read more.
High-performance structural materials (HPSMs) are needed for the successful and safe design of fission and fusion reactors. Their operation is associated with unprecedented fluxes of high-energy neutrons and thermomechanical loadings. In fission reactors, HPSMs are used, e.g., for fuel claddings, core internal structural components and reactor pressure vessels. Even stronger requirements are expected for fourth-generation supercritical water fission reactors, with a particular focus on the HPSM’s corrosion resistance. The first wall and blanket structural materials in fusion reactors are subjected not only to high energy neutron irradiation, but also to strong mechanical, heat and electromagnetic loadings. This paper presents a historical and state-of-the-art summary focused on the properties and application potential of irradiation-resistant alloys predominantly strengthened by an oxide dispersion. These alloys are categorized according to their matrix as ferritic, ferritic–martensitic and austenitic. Low void swelling, high-temperature He embrittlement, thermal and irradiation hardening and creep are typical phenomena most usually studied in ferritic and ferritic martensitic oxide dispersion strengthened (ODS) alloys. In contrast, austenitic ODS alloys exhibit an increased corrosion and oxidation resistance and a higher creep resistance at elevated temperatures. This is why the advantages and drawbacks of each matrix-type ODS are discussed in this paper. Full article
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12 pages, 2298 KiB  
Article
Supercritical Water: A Simulation Study to Unravel the Heterogeneity of Its Molecular Structures
by Joseph Guy Gérard Ndongo Assomo, Sadollah Ebrahimi, Jean-Paul Jay-Gerin and Armand Soldera
Molecules 2024, 29(12), 2947; https://doi.org/10.3390/molecules29122947 - 20 Jun 2024
Cited by 3 | Viewed by 1523
Abstract
(1) Background: In the quest to accurately model the radiolysis of water in its supercritical state, a detailed understanding of water’s molecular structure, particularly how water molecules are arranged in this unique state, is essential. (2) Methods: We conducted molecular dynamics simulations using [...] Read more.
(1) Background: In the quest to accurately model the radiolysis of water in its supercritical state, a detailed understanding of water’s molecular structure, particularly how water molecules are arranged in this unique state, is essential. (2) Methods: We conducted molecular dynamics simulations using the SPC/E water model to investigate the molecular structures of supercritical water (SCW) over a wide temperature range, extending up to 800 °C. (3) Results: Our results show that at a constant pressure of 25 MPa, the average intermolecular distance around a reference water molecule remains remarkably stable at ~2.9 Å. This uniformity persists across a substantial temperature range, demonstrating the unique heterogeneous nature of SCW under these extreme conditions. Notably, the simulations also reveal intricate patterns within SCW, indicating the simultaneous presence of regions with high and low density. As temperatures increase, we observe a rise in the formation of molecular clusters, which are accompanied by a reduction in their average size. (4) Conclusions: These findings highlight the necessity of incorporating the molecular complexity of SCW into traditional track-structure chemistry models to improve predictions of SCW behavior under ionizing radiation. The study establishes a foundational reference for further exploration of the properties of supercritical water, particularly for its application in advanced nuclear technologies, including the next generation of water-cooled reactors and their small modular reactor variants that utilize SCW as a coolant. Full article
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16 pages, 2792 KiB  
Article
Gasification of Lignocellulosic Waste in Supercritical Water: Study of Thermodynamic Equilibrium as a Nonlinear Programming Problem
by Julles Mitoura dos Santos Junior and Adriano Pinto Mariano
Eng 2024, 5(2), 1096-1111; https://doi.org/10.3390/eng5020060 - 12 Jun 2024
Cited by 1 | Viewed by 1195
Abstract
As one of the main industrial segments of the current geoeconomics scenario, agro-industrial activities generate excessive amounts of waste. The gasification of such waste using supercritical water (SCWG) has the potential to convert the waste and generate products with high added value, hydrogen [...] Read more.
As one of the main industrial segments of the current geoeconomics scenario, agro-industrial activities generate excessive amounts of waste. The gasification of such waste using supercritical water (SCWG) has the potential to convert the waste and generate products with high added value, hydrogen being the product of greatest interest. Within this context, this article presents studies on the SCWG processes of lignocellulosic residues from cotton, rice, and mustard husks. The Gibbs energy minimization (minG) and entropy maximization (maxS) approaches were applied to evaluate the processes conditioned in isothermal and adiabatic reactors, respectively. The thermodynamic and phase equilibria were written as a nonlinear programming problem using the Peng–Robinson state solution for the prediction of fugacity coefficients. As an optimization tool, TeS (Thermodynamic Equilibrium Simulation) software v.10 was used with the help of the trust-constr algorithm to search for the optimal point. The simulated results were validated with experimental data presenting surface coefficients greater than 0.99, validating the use of the proposed modeling to evaluate reaction systems of interest. It was found that increases in temperature and amounts of biomass in the process feed tend to maximize hydrogen formation. In addition to these variables, the H2/CO ratio is of interest considering that these processes can be directed toward the production of synthesis gas (syngas). The results indicated that the selected processes can be directed to the production of synthesis gas, including the production of chemicals such as methanol, dimethyl ether, and ammonia. Using an entropy maximization approach, it was possible to verify the thermal behavior of reaction systems. The maxS results indicated that the selected processes have a predominantly exothermic character. The initial temperature and biomass composition had predominant effects on the equilibrium temperature of the system. In summary, this work applied advanced optimization and modeling methodologies to validate the feasibility of SCWG processes in producing hydrogen and other valuable chemicals from agro-industrial waste. Full article
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16 pages, 2204 KiB  
Article
Investigating Salt Precipitation in Continuous Supercritical Water Gasification of Biomass
by Julian Dutzi, Nikolaos Boukis and Jörg Sauer
Processes 2024, 12(5), 935; https://doi.org/10.3390/pr12050935 - 3 May 2024
Cited by 4 | Viewed by 1801
Abstract
The formation of solid deposits in the process of supercritical water gasification (SCWG) is one of the main problems hindering the commercial application of the process. Seven experiments were conducted with the grass Reed Canary Grass with different preheating temperatures, but all ended [...] Read more.
The formation of solid deposits in the process of supercritical water gasification (SCWG) is one of the main problems hindering the commercial application of the process. Seven experiments were conducted with the grass Reed Canary Grass with different preheating temperatures, but all ended early due to the formation of solid deposits (maximum operation of 3.8 h). The position of solid deposits in the lab plant changed with the variation in the temperature profile. Since the formation of solid deposits consisting of salts, coke, and corrosion products is a severe issue that needs to be resolved in order to enable long-time operation, inner temperature measurements were conducted to determine the temperature range that corresponds with the zone of solid formation. The temperature range was found to be 400 to 440 °C. Wherever this temperature was first reached solid deposits occurred in the system that led to blockage of the flow. Additional to the influence of the temperature, the influence of the flow direction (up-flow or down-flow) on the operation of the continuous SCWG plant was examined. If salts are not separated from the system sufficiently, up-flow reactors should be avoided because they amplify the accumulation of solid deposits leading to a shortened operation time. The heating concept coupled with the salt separation needs to be redesigned in order to separate the salts before entering the gasification reactors. Outside of the determined temperature zone no deposition was visible. Thus, even though the gasification efficiency was low it could be shown that the operation was limited to the deposits forming in the heating section and not by incomplete gasification in the reactor where T > 600 °C. Full article
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