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This article presents the results of an experimental study of the coolant flow in a fuel rod bundle of a nuclear reactor fuel assembly of a small modular reactor for a small ground-based nuclear power plant. The aim of the work is to experimentally determine the hydrodynamic characteristics of the coolant flow in a fuel rod bundle of a fuel assembly. For this purpose, experimental studies were conducted in an aerodynamic model that included simulators of fuel elements, burnable absorber rods, spacer grids, a central displacer, and stiffening corners. During the experiments, the water coolant flow was modeled using airflow based on the theory of hydrodynamic similarity. The studies were conducted using the pneumometric method and the contrast agent injection method. The flow structure was visualized by contour plots of axial and tangential velocity, as well as the distribution of the contrast agent. During the experiments, the features of the axial flow were identified, and the structure of the cross-flows of the coolant was determined. The database obtained during the experiments can be used to validate CFD programs, refine the methods of thermal-hydraulic calculation of nuclear reactor cores, and also to justify the design of fuel assemblies. [ABSTRACT FROM AUTHOR]

Marine sources contribute approximately 2% of global energy-related CO₂ emissions, with the shipping industry accounting for 87% of this total, making it the fifth-largest emitter globally. Environmental regulations by the International Maritime Organization (IMO), such as the MARPOL (International Convention for the Prevention of Pollution from Ships) treaty, have driven the exploration of alternative green energy solutions, including nuclear-powered ships. These ships offer advantages like long operational periods without refueling and increased cargo space, with around 200 reactors already in use on naval vessels worldwide. Among advanced reactor concepts, the molten salt reactor (MSR) is particularly suited for marine applications due to its inherent safety features, compact design, high energy density, and potential to mitigate nuclear waste and proliferation concerns. However, MSR systems face significant challenges, including tritium production, corrosion issues, and complex behavior of volatile fission products. Understanding the impact of marine-induced motion on the thermal–hydraulic behavior of MSRs is crucial, as it can lead to transient design basis accident scenarios. Furthermore, the adoption of MSR technology in the shipping industry requires overcoming regulatory hurdles and achieving global consensus on safety and environmental standards. This review assesses the current progress, challenges, and technological readiness of MSRs for marine applications, highlighting future research directions. The overall technology readiness level (TRL) of MSRs is currently at 3. Achieving TRL 6 is essential for progress, with individual components needing TRLs of 4–8 for a demonstration reactor. Community Readiness Levels (CRLs) must also be addressed, focusing on public acceptance, safety, sustainability, and alignment with decarbonization goals. [ABSTRACT FROM AUTHOR]

A miniature nuclear reactor is desirable for deployment as a localized nuclear power station in support of a carbon-free power supply. Coupling aspects of proliferation-resistant fuel with natural burnable absorber loading are evaluated for once-through operation cycle performance to minimize the need for refueling and fuel shuffling operations. The incorporation of 0.075 wt.% 237Np provides favorable plutonium isotopic vectors throughout an operational lifetime of 5.5 years. providing 35 MWe. Core performance was assessed using a verification-by-comparison approach for core designs with or without 237Np and/or gadolinia burnable absorber. Burnup Monte Carlo calculations were performed via MCOS coupling of MCNP and ORIGEN to an achievable burnup of ~62.5 GWd/t. The results demonstrate a minimal penalty to reactor performance due to the addition of these materials as compared against the reference design. Coupling of a proliferation-resistant fuel concept with a uniform loading of natural gadolinia burnable absorber for LEU+ fuel (7.5 wt.% 235U/U UO2) provides favorable excess reactivity considerations with minimized concerns for additional residual waste and more uniform distribution of un-depleted 235U in discharged fuel assemblies. [ABSTRACT FROM AUTHOR]

Small nuclear power plants are a promising direction of research for the development of carbon-free energy in isolated power systems and in remote regions with undeveloped infrastructure. Improving the efficiency of power units integrated with small modular reactors will improve the prospects for the commercialization of such projects. Power cycles based on supercritical carbon dioxide are an effective solution for nuclear power plants that use reactor facilities with an initial coolant temperature above 550 °C. However, the presence of low temperature rejected heat sources in closed Bryton cycles indicates a potential for energy saving. This paper presents a comprehensive thermodynamic analysis of the integration of an additional low-temperature organic Rankine cycle for heat recovery to supercritical carbon dioxide cycles. A scheme for sequential heat recovery from several sources in S-CO2 cycles is proposed. It was found that the use of R134a improved the power of the low-temperature circuit. It was revealed that in the S-CO2 Brayton cycle with a recuperator, the ORC add-on increased the net efficiency by an average of 2.98%, and in the recompression cycle by 1.7–2.2%. With sequential heat recovery in the recuperative cycle from the intercooling of the compressor and the main cooler, the increase in efficiency from the ORC superstructure will be 1.8%. [ABSTRACT FROM AUTHOR]

Small nuclear power plants can provide a stable, carbon-free energy supply to civil infrastructure and industrial enterprises in remote regions isolated from unified energy systems. More than 70 projects of small modular reactors are currently being developed by IAEA member countries; several low-power power units are already supplying thermal and electrical energy to consumers. One of the main limitations standing in the way of widespread dissemination of this technology is the high specific capital cost of a low-power nuclear power plant; therefore, new scientific and technical solutions are needed in this industry. Increasing the thermodynamic efficiency of power cycles of small modular reactors can become a driver for reducing the cost of supplied electrical energy. This paper presents the results of a comprehensive thermodynamic analysis of existing and promising power cycles for small modular reactors. In addition to traditional steam power cycles, cycles using non-traditional working fluids, including carbon dioxide, freons, and helium cycles, are considered. Optimal sets of thermodynamic parameters were determined to ensure maximum net efficiency of electricity production. For water-cooled reactor plants, a maximum efficiency of 33.5% at an initial temperature of 300 °C could be achieved using a steam turbine cycle. It was revealed that for reactor plants with liquid metal and liquid salt coolant in the range of initial temperatures above 550–700 °C, the maximum thermal efficiency was provided by the Brayton recompression cycle with a carbon dioxide coolant: the net electrical efficiency exceeded the level of steam turbine plants, with intermediate superheating of the steam, and could reach a value of 49.4% at 600 °C. This makes the use of these cycles promising for low-power nuclear power plants with a high initial temperature. In small gas-cooled reactor plants with a helium coolant, the use of a binary cycle consisting of a helium Brayton cycle and a steam-powered Rankine cycle provided an efficiency of 44.3% at an initial helium temperature of 700 °C and 52.9% at 1000 °C. This was higher than in the Brayton cycle with a recuperator, with a minimum temperature difference in the heat exchanger of 20 °C: the efficiency was 40.2% and 52%, respectively. Also, the transition to power cycles with non-traditional working fluids will lead to a change in the operating conditions of turbomachines and heat exchangers. [ABSTRACT FROM AUTHOR]

Small modular reactors with power below 300 MW have the advantages of small specific mass, long lifetime, and flexible power supply, and they are suitable for providing power support for small and medium-sized towns with small populations and remote areas without grid coverage. In this paper, a small modular S-CO2-cooled molten salt reactor is proposed, and the design of a 10 MW small modular chlorine salt fast reactor (sm-MCFR) with 20 years of operation without refueling is presented. The neutron feasibility of the S-CO2-cooled small modular chlorine fast reactor is analyzed in terms of neutron energy spectrum, reactivity control, temperature reactivity coefficient, and power distribution. A distinctive feature of the sm-MCFR is the use of chlorine salts with high heavy metal solubility and a hard energy spectrum, allowing the core size to be minimized while maintaining the maximum lifetime. The designed core is about 2.44 m in diameter and 2.24 m in height. Meanwhile, the sm-MCFR uses control drum control as the control system, which can effectively achieve reactivity control without increasing the reactor size. The final optimized sm-MCFR has a negative temperature reactivity coefficient, which is necessary to ensure the safe operation of the reactor. [ABSTRACT FROM AUTHOR]

Neutron thermalization leads to the complexity of the scattering cross-section calculation, which influences the accuracy of the neutron transport calculation in the thermal energy range. The higher precision of thermal scattering data is demanded in the small modular reactors (SMRs) design, especially for small-sized PWRs and SCWRs. Additionally, the thermal neutron scattering problems in supercritical water have not yet been solved. In this study, the thermal neutron scattering problems in subcritical water are tested. Based on thermal neutron scattering theory, the GA model and IKE model were analyzed. This work selected the corresponding input parameters, such as the frequency spectrum, the discrete oscillator energy, weight parameters and so on, as well as preliminary studies on how to calculate the thermal scattering data for HinH2O to accomplish the calculation at various temperatures by developing LIPER code. The deviation between the calculated and reference results, which were both obtained by the Monte Carlo code, COSRMC, was below 0.2 pcm. The deviation of the scattering cross-section between the calculation results and reference was below 0.1%, indicating the reasonability of this study's thermal scattering data calculation. [ABSTRACT FROM AUTHOR]

Most power plants, particularly those that burn fossil fuels such as coal, oil, and gas, create CO2, a greenhouse gas that contributes to climate change. By 2060, the Indonesian government has committed to reach net zero emissions. With the lowest CO2 emissions, nuclear power plants are dependable sources of energy. Small modular reactors (SMRs) are a particular kind of nuclear power plant that has the potential to be Indonesia's first commercial nuclear power plant because of their small size, low capacity, uncomplicated design, and modular characteristics. The purpose of this study is to examine the economics and technological feasibility of SMRs. In this analysis, the levelized cost of electricity (LCOE) comparative method and the technology readiness level (TRL) approach are both applied. The SMRs with a minimum TRL value of 7 were CAREM-25 (TRL7), KLT-40S (TRL8), and HTR-PM (TRL 8), according to the results of this research. Although CAREM-25 and KLT-40S are still in the demonstration stage and have not yet entered the market, their LCOE estimates are greater than 0.07 USD/kWh with a 5% discount rate. Whereas CAREM 100 MW is an economy scale from CAREM-25 and VBER 300 MW is a commercial size from KLT-40S, HTR-PM is already an economy scale. With discount rates between 5% and 10%, the LCOE values of HTR-PM, CAREM 100 MW, and VBER 300 MW range from 0.06 USD to 0.12 USD per kWh. Other than hydropower and coal-fired power plants, these LCOE figures can compete with the local LCOE in Indonesia and the LCOE of a variety of other types of power plants. [ABSTRACT FROM AUTHOR]

This scientific paper discusses the importance of reducing greenhouse gas emissions to mitigate the effects of climate change. The proposed strategy is to reach net-zero emissions by transitioning to electric systems powered by low-carbon sources such as wind, solar, hydroelectric power, and nuclear energy. However, the paper also highlights the challenges of this transition, including high costs and lack of infrastructure. The paper emphasizes the need for continued research and investment in renewable energy technology and infrastructure to overcome these challenges and achieve a sustainable energy system. Additionally, the use of nuclear energy raises concerns, such as nuclear waste and proliferation, and should be considered with its benefits and drawbacks. The study assesses the feasibility of nuclear energy development in Latvia, a country in Northern Europe, and finds that Latvia is a suitable location for nuclear power facilities due to potential energy independence, low-carbon energy production, reliability, and economic benefits. The study also discusses methods of calculating electricity generation and consumption, such as measuring MWh produced by power plants, and balancing supply and demand within the country. Furthermore, the study assesses the safety of nuclear reactors, generated waste, and options for nuclear waste recycling. The transition to a carbon-free energy system is ongoing and complex, requiring multiple strategies to accelerate the transition. While the paper proposes that nuclear energy could be a practical means of supporting and backing up electricity generated by renewables, it should be noted that there are still challenges to be addressed. Some of the results presented in the paper are still based on studies, and the post-treatment of waste needs to be further clarified. [ABSTRACT FROM AUTHOR]

Advanced small modular reactors (SMRs) have recently been developed in many designs; therefore, nuclear energy stands out as a promising alternative to sustainability and reliability in replacing fossil fuel energies in microgrids. SMRs have been shown as the best option due to the fact of their lower initial capital, greater scalability, and siting flexibility compared to large nuclear plants. Nowadays, there are several simulators able to reproduce all the safety and control mechanics of different nuclear reactors; however, there exists a lack of emulators able to put these functionalities into a real scenario to ensure the feasibility of the use of nuclear energy within energy systems, especially in nonconventional systems. This paper aims to mimic the central control system of SMRs by modeling the nuclear processes aiming to contribute to real-time simulations using SMRs integrated with renewable energy in microgrids that could be applied for different scenarios, such as cogeneration systems or fast-charging stations for electric vehicles, by considering the impact on dispatch and reliability. The simulation process of the proposed model was validated experimentally using the hardware-in-the-loop technique, which consisted of the modeling being integrated into the hardware and tested using real-time simulators. The proposed system, also denominated as SMR-in-the-Loop, was designed and adapted to be easily integrated with existing microgrid systems to represent the behavior of an SMR in nuclear-renewable hybrid energy systems, avoiding high investments and complexity in testing and implementing actual nuclear reactors. [ABSTRACT FROM AUTHOR]

Small modular reactors (SMRs) are those nuclear fission reactors with electrical output powers of less than 300 MWe. Due to its inherent safety features, the modular high temperature gas-cooled reactor (MHTGR) has been seen as one of the best candidates for building SMR-based nuclear plants with high safety-level and economical competitive power. Power-level control is crucial in providing grid-appropriation for all types of SMRs. Usually, there exists nonlinearity, parameter uncertainty and control input saturation in the SMR-based plant dynamics. Motivated by this, a novel saturated adaptive output-feedback power-level control of the MHTGR is proposed in this paper. This newly-built control law has the virtues of having relatively neat form, of being strong adaptive to parameter uncertainty and of being able to compensate control input saturation, which are given by constructing Lyapunov functions based upon the shifted-ectropies of neutron kinetics and reactor thermal-hydraulics, giving an online tuning algorithm for the controller parameters and proposing a control input saturation compensator respectively. It is proved theoretically that input-to-state stability (ISS) can be guaranteed for the corresponding closed-loop system. In order to verify the theoretical results, this new control strategy is then applied to the large-range power maneuvering control for the MHTGR of the HTR-PM plant. Numerical simulation results show not only the relationship between regulating performance and control input saturation bound but also the feasibility of applying this saturated adaptive control law practically. [ABSTRACT FROM AUTHOR]

The most important target of the concept "sustainability" is to achieve fairness between generations. Its expanding interpolation leads to achieve fairness within a generation. Thus, it is necessary to discuss the role of nuclear power from the viewpoint of this definition. The history of nuclear power has been the control of the nuclear fission reaction. Once this is obtained, then the economy of the system is required. On the other hand, it is also necessary to consider the internalization of the external diseconomy to avoid damage to human society caused by the economic activity itself, due to its limited capacity. An extreme example is waste. Thus, reducing radioactive waste resulting from nuclear power is essential. Nuclear non-proliferation must be guaranteed. Moreover, the FUKUSHIMA accident revealed that it is still not enough that human beings control nuclear reaction. Further, the most essential issue for sustaining use of one technology is human resources in manufacturing, operation, policy-making and education. Nuclear power will be able to satisfy the requirements of sustainability only when these subjects are addressed. The author will review recent activities of a thorium molten-salt reactor (MSR) as a cornerstone for a sustainable society and describe its objectives and forecasts. [ABSTRACT FROM AUTHOR]

The dissolution behavior of magnetite deposited on flow mini-channel surfaces within a printed circuit heat exchanger (PCHE) and the corrosion behavior of a STS 316L PCHE material were investigated in an ethylendiaminetetraacetic acid (EDTA)-based chemical cleaning solution at 93 °C. The fouling in the PCHE was simulated using a water-steam circulation loop system. Most of the magnetite deposits were rapidly dissolved in the early stage of the circulation chemical cleaning. An empirical equation for estimating the dissolution percentage was derived as a function of cleaning time. The PCHE material showed excellent corrosion resistance during the chemical cleaning tests. These results indicate the fouling layers in the PCHEs can be removed efficiently by the chemical cleaning process without concern about base metal corrosion. [ABSTRACT FROM AUTHOR]

Most of the small modular reactors (SMRs) under development worldwide present the same components: an integral reactor vessel with a low-positioned core as the heat source and a high-positioned steam generator as the heat sink. Moreover, some SMRs are being designed to be driven by natural circulation during normal power generation. This work focused on such designs and on their performance, considering the changes generated by the geometric and hydraulic parameters of the system. Numerical simulations using mass, momentum, and energy equations that considered buoyancy forces were performed to determine the effects of various geometric and hydraulic parameters, such as diameters and flow resistances, on the reactor's performance. It was found that nonuniform diameters promote velocity changes that affect the natural circulation flow rate. Moreover, the reactor's temperature distribution depends on the steam generator tube pitch. Therefore, the hydraulic diameters of the reactor's coolant passages should be maintained as uniform as possible to obtain a more uniform temperature distribution and a larger mass flow rate in SMRs. [ABSTRACT FROM AUTHOR]

Small Modular Reactors (SMRs) have been recognized to have potential in decarbonizing district heating, which is currently an urgent sustainability challenge in many European countries. In this paper, the financial impacts of replacing peat and biomass-powered Combined Heat and Power (CHP) plants with heat-only reactors of 24–200 MW power range and maximum output temperatures of 120 °C are studied. A district heating system of a medium-sized Nordic city in Eastern Finland is modeled with EnergyPRO computer software (EMD International A/S, Aalborg, Denmark), which is used to optimize plant units' production for cost effectiveness. A future scenario is used to predict electricity prices, expenditures from CO2 emission allowances, and fuel prices for the studied case. Results show that the low operating expenditures of CO2 free heat-only reactors would compensate for the revenue losses from electricity sales and that a small number of micro reactors, with power output in the tens of megawatts range each, would be optimal for the studied case. Since investment cost estimates for SMRs still bear significant uncertainties, the subject should be followed in further studies, as heat-only SMRs could provide a profitable alternative for current CHP production in the future. [ABSTRACT FROM AUTHOR]

A Small Modular Reactor’s (SMR) containment vessel (CNV) is submerged in the reactor cooling pool, which supplies a passive heat sink for containment to remove heat during Loss of Coolant Accident (LOCA). The heat transfer efficiency of passive safety systems is affected by thermal stratification processes. This study aims to explain the phenomenon of thermal stratification in SMR’s reactor pool. A small scaled containment vessel with an electric heater inside immersed in a pool of water was used to simulate this phenomenon. The results show how the thermal stratification formed. Moreover, a three-dimensional computational fluid dynamic (CFD) model was built using ANSYS FLUENT. Experimental data were compared with simulation results, and the standard k-ε model was found to be suitable for calculating thermal stratification in the pool outside the containment. [ABSTRACT FROM AUTHOR]