Modular Reactor Research Articles

Design and analysis on the HP-PHRS for small modular lead-bismuth fast reactor

The heat pipe is an efficient heat-conducting element that can efficiently and passively transfer heat from a high-temperature heat source to a low-temperature heat source. It is widely used in the various industries. Based on high-temperature heat pipe technology, this paper designs a passive decay heat removal system for a small modular lead–bismuth fast reactor, and uses the system code ATHLET coupled with the heat pipe calculation module to calculate and analyze the thermal–hydraulic characteristics of the reactor under station black out accident.

Supercritical Water: A Simulation Study to Unravel the Heterogeneity of Its Molecular Structures.

(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.

Seismic performance enhancement of small modular reactors using optimal design of inerter-based vibration absorbers

Nuclear power plant (NPP) structures face significant challenges in ensuring structural resilience subjected to earthquake motions. The inerter-based vibration absorbers (IVAs) have been proven to control structural vibration, but they have not been applied in small modular reactor (SMR) structures. In this study, the optimal IVA parameters are investigated for SMR structures, which focus on reducing the seismic response of the first floor and fifth floor. By using a genetic algorithm (GA), the IVAs parameters are optimized to minimize the storey displacement variance and storey acceleration variance. Besides, the robustness analysis is performed to ensure the optimized parameters are practical. The various ground motions are selected for time history analysis (THA) to illustrate the seismic response of SMR equipped with the optimal IVAs. The results of THA demonstrate that the optimal IVAs enhance the seismic performance of the SMR compared with traditional SMR structures. By positioning optimal IVAs, significant mitigation of both storey displacement and storey acceleration are achieved. This study explores to a deeper understanding of IVAs' efficacy in SMR structures, which is beneficial to the practical use of IVAs in SMR structures.

Nuclear engineering and design nuclear heat supply system for a small district heating reactor

Small Modular Reactors (SMRs) are currently considered to be a potential solution for decarbonizing the district heating sector. The LUT Heat Experimental Reactor (LUTHER) is a concept for a small modular nuclear heating plant that is being designed to meet the demands of Nordic district heating networks while also incorporating high safety standards. This paper presents an extension of the work pursued by LUT University by proposing a reactor module that allows for easy scaling of unit sizes ranging from 2 MW to 120 MW. The pressure tube assembly geometry, which has been developed specifically for the LUTHER reactor module, was analyzed by modeling two significantly different-sized variants that utilize this unique structure. The modular design of LUTHER enables complete factory-assembly and the use of standard road transport for unit sizes up to 120 MW. This design prioritizes high inherent safety, targeting for siting near population centers. The proposed heating reactor concept offers a viable means of decarbonizing the district heating sector by replacing existing combustion-based production with emissions-free nuclear heat.

Regulation vs promotion: Small modular nuclear reactors in Canada

Canada is planning to construct a set of new and hitherto untested nuclear reactor designs called Small Modular Reactors. The government has incentivised this process by providing tens of millions of dollars to companies developing these designs. In this paper, we describe two problems with the process of regulating these technologies. The first problem is evidence of institutional bias within the federal regulatory body that is tasked with regulating these technologies. Using the case of small modular reactors, this paper details how the regulator's actions do not suggest unbiased decision making. The second problem is the exclusion of small modular nuclear reactors from the Impact Assessment process. As a result, the discussion about whether to construct these reactors will be based on an incomplete understanding of the full environmental consequences of the decision to build. Finally, we offer policy recommendations to address these problems.

Verification of the Coupled Code PARCS/TWOPORFLOW with Rod Ejection Accident Calculations for Small Modular Reactors

Research on small modular reactors (SMRs) is gaining importance since they are key for addressing energy challenges in various sectors. These types of reactors integrate novel technologies that rely heavily on passive safety systems. Among the most developed light water reactors, SMR designs are SMART and NuScale. This work analyzes the academic boron-free Karlsruhe Small Modular Reactor (KSMR), which may fit in SMART, and a core design resembling NuScale. The research aims to explore the potential of new multiphysics tools under development to predict safety parameters of SMRs during normal operation and transients. For this purpose, the Purdue Advanced Reactor Core Simulator (PARCS) and TWOPORFLOW (TPF) codes have been coupled using the Interface for Code Coupling (ICoCo), orchestrating code execution through a C++ Supervisor program. In this work, a nodewise rod ejection accident (REA) has been analyzed for two different scenarios. The first is a hot-zero-power scenario for the KSMR core, and the second is initiated at 75% of nominal power for the NuScale core. Verification of results has been done though code-to-code comparison. Comparison of the PARCS/TPF results obtained for both KSMR and NuScale with reference cases shows acceptable differences. Key safety parameters predicted by the codes for the REA analysis of both cores have also been evaluated against the latest U.S. Nuclear Regulatory Commission regulation for reactivity initiated accidents showing that all parameters fulfill core coolability acceptance criteria and fuel rod cladding failure thresholds. The presented work highlights the transition from the coupling of PARCS with a mixture model code, such as SCF, to a coupling with a two-phase model code, such as TPF. These findings contribute to a better understanding of SMR phenomenology during accidental sequences and demonstrate the capabilities of the coupled codes.

Investigation of Natural Helium Circulation Inside Dual Channels Prismatic Modular Reactor

Natural helium circulation inside a dual-channel prismatic modular reactor was numerically investigated to comprehend the passive safety features using the new RHYS/ASYST VER4 package. The natural circulation was studied at Depressurized Cooldown (DC) at heat fluxes of 860–2293 W/m2 with a pressure of 413.7 kPa and Pressurized Cooldown (PC) at pressures of 413.47–689.12 kPa with a flux of 1720 W/m2. A reversal of the heat transfer near the riser exit was seen, combined with a decrease in helium and riser wall temperatures due to the end effect. The pressure has an inverse effect on the heat transfer, where the temperature decreases by 19 % as the pressure increases from 413.47 to 689.12 kPa. The heat transfer was studied under the DC and PC. Both entrance and end effects are introduced with the heat transfer coefficient. Also, the nondimensional groups (Nu, Gr, Pr, and Ra) were discussed.

Accident tolerant fuel design optimization for SMART reactor

Fully Ceramic Microencapsulated (FCM) fuel is one of the most advancedfuel types for the next nuclear reactor generations. The use of uranium carbide fuel in FCM offers multiple benefits such as high fuel density, improved thermal conductivity and enhanced mechanical stability. Both UC and conventional fuel (UO2) have the same melting point. As a result, under reactor operating conditions, UC has better safety margins. In addition, FeCrAl is a promising cladding material. However, because of its greater thermal neutron absorption cross section, FeCrAl has a neutronic penalty when compared to Zircaloy leading to an annual reload requirement with high fuel enrichment. Owing to their low power density and excellent design, small modular reactors (SMRs) have exceptional inherent safety. In this work, we determined the optimum design of an accident tolerant fuel (ATF), with respect to neutronics, in SMART reactor using dense UC FCM (in contrast to the conventional UO2 fuel) and a combination of zircalloy and FeCrAl (FCM -Zircaloy, FCM -FeCrAl, FCM -combining of zircaloy and FeCrAl) as cladding to achieve better thermal conductivity as well as safer performance, while considering the required fuel enrichment for the proposed designs. The effective multiplication factor and burnup were calculated for neutronic assessment of the SMART core, the outcomes are showcased alongside a comprehensive assessment of the characteristics and prospective. The neutronic parameters were estimated using the stochastic MCNPX 2.6 code. We found that Fully Ceramic Microencapsulated -Uranium Carbide (FCM-UC) fuel type was more attractive than conventional UO2. The optimum cladding design as compared to the reference case and the other cases of (FCM-UC), was determined. When 50% FeCrAl cladding was employed, case 15 in our study emerged as the superior design, demonstrating maximum production of 239Pu due to higher initial concentrations of 235U and quantities of 238U. This work may offer recommendations for future optimized designs of the SMART reactor parameters.

Modular Cascade of Flow Reactors: Continuous Flow Synthesis of Water-Insoluble Diazo Dyes in Aqueous System.

Continuous flow synthesis is pivotal in dye production to address batch-to-batch variations. However, synthesizing water-insoluble dyes in an aqueous system poses a challenge that can lead to clogging. This study successfully achieved the safe and efficient synthesis of azo dyes by selecting and optimizing flow reactor modules for different reaction types in the two-step reaction and implementing cascade cooperation. Integrating continuous flow microreactor with continuous stirred tank reactor (CSTR) enabled the continuous flow synthesis of Sudan Yellow 3G without introducing water-soluble functional groups or using organic solvents to enhance solubility. Optimizing conditions (acidity/alkalinity, temperature, residence time) within the initial modular continuous flow reactor resulted in a remarkable 99.5% isolated yield, 98.6 % purity, and a production rate of 2.90 g h-1. Scaling-up based on different reactor module characteristics further increased the production rate to 74.4 g h-1 while maintaining high yield and purity. The construction of this small 3D-printing modular cascaded reactor and process scaling-up provide technical support for continuous flow synthesis of water-insoluble dyes, particularly high-market-share azo dyes. Moreover, this versatile methodology proves applicable to continuous flow processes involving various homogeneous and heterogeneous reaction cascades.

Site effect on seismic response of buried nuclear power plant structure

The development of multifunctional, multipurpose small modular next generation nuclear reactors has become a trend in designing small-scale nuclear power stations. In this study, taking a new next-generation buried nuclear power structure as the target structure, a 3D finite element model of the site-nuclear power plant structure system was established, and its response at different sites was studied. Using the internal substructure method, this study initially explored the impact of earthquake input and artificial boundary locations on the structural response. The results indicate that the internal substructure method enhances computational efficiency without compromising accuracy. For this model, it is recommended to input earthquake motion close to the structure, set the lateral boundary location to three times the width of the structure, and set the bottom boundary location to two times the depth of the structure. Subsequently, an investigation into the response of the structure at varying site wave velocities is conducted. The results show that as the wave velocity increases, the acceleration response intensifies, while the displacement response diminishes. However, the relationship is nonlinear; the response exhibits less variation with increasing site wave velocity. The seismic response of a structure is profoundly influenced by site conditions, emphasizing the imperative need for careful consideration of specific site characteristics in seismic analyses. In addition, the response pattern of the overall structure is significantly different from that of conventional large surface-sited nuclear power plants, and further research should be conducted on the seismic response characteristics of buried nuclear power plants.

Potential role of nuclear power in a carbon-free world

Thermal Power Plants (ThPP), along with transport facilities, are the major sources for industrial emissions of carbon dioxide (CO2) believed to be responsible for the greenhouse effect leading to overheating of the lower atmosphere. In the opinion of many scientists, there is a threshold value of the average atmospheric temperature exceeding, which entails the potential for the development of irreversible processes threatening the existence of humankind. To avoid this danger, governments in nearly 200 countries have chosen voluntarily to reach net-zero CO2 emissions by 2050. Renewable Energy Sources (RES), including wind and solar power plants, have been selected as substitutes for ThPPs. However, energy systems based on RES only need to be multiply redundant in terms of installed capacity due to their efficiency being heavily dependent on daily, seasonal and weather factors, leave alone the scale of the required material resources (metals, polymers, concrete, glass, etc.). The major drawback of such energy systems is, however, the RES common-cause failure, e.g., in the event of a global volcanic eruption, when no energy-security requirement can be met to provide energy for satisfying the most vital needs. A need is fully evident for furnishing such energy system with another power source to be not dependent on the event that has caused the mass RES failure. With the net-zero-carbon requirement taken into account, Nuclear Power (NP) appears to be the best option in this respect. Modern NP does not however fully suits this role due to its inherent drawbacks (limited fuel resources, pending Spent Nuclear Fuel (SNF) and RadioActive Wastes (RAW) handling and nuclear-material nonproliferation issues). A potential solution to these drawbacks is a two-component NP technology in a closed nuclear-fuel cycle currently in the process of development. In Russia, where the greatest progress has been achieved in this field of development, under construction is a pilot and demonstration energy complex with the BREST-OD-300 nuclear unit expected to be started up in 2026–2027. Another promising designs to be developed are Small Modular Reactors (SMRs) / Small Nuclear Power Plants (SNPPs).

Controversy or Consensus: Launching Small Modular Nuclear Reactors in Romania

Abstract The transition towards net zero by 2050 is underway in the European Union, but its country members are divided over their energy strategies. France, Poland, Hungary, Bulgaria, Slovakia, and Romania support nuclear plants as contributing to carbon neutrality, while Germany, Spain, Denmark, Portugal, and Luxembourg oppose (Reuters, 2023). The study “Between Stability and Sustainability: Nuclear Energy in Romania's Energy Mix” concludes that Romania can benefit from its nuclear facilities and domestic uranium resources, to consolidate its sustainable energy policy. However, new nuclear capacities may pose considerable challenges, especially in terms of costs (Dumitrescu, 2023). Unfortunately, rising costs per megawatt hour are the very reason why NuScale, the operator chosen by Romania to deploy six small nuclear reactors by 2027, canceled their US-based flagship Carbon Free Power Project (Fortune, 2023). Nevertheless, the setback in the home country did not prevent Romanian authorities from licensing the NuScale small modular reactor power plant in Doicești (World Nuclear News, 2023). The watchdog Greenpeace warned about the project’s high costs and the long construction timeframe. It was also emphasized that Romania adopted a technology that had never been tested before. In addition, the location of the new plant had been decided without prior consultation from the local community, claimed the NGO (Greenpeace, 2022). According to the journalists, the local community has been divided between those who want new jobs and people afraid of radiations. Reporters made a parallel between the current situation and a formerly failed Chevron shale gas production investment, due to the strong opposition to fracking (Hotnews, 2024). This paper attempts to determine how a newcomer to the nuclear energy market, with a significant approval setback in its home country, using untested technology, can complete the construction of six small modular reactors in Romania, integrate those into the national grid and win over the public acceptance by 2030.

Small Modular Reactors in Romania’s Energy Future. Two Essential Perspectives: Capital Costs and Public Perception

Abstract In 2023, during the annual United Nations Conference on Climate Change (COP28), Romania joined the Net Zero Nuclear Initiative and the Ministerial Declaration for the tripling of nuclear capacity by 2050, which recognizes the key role of nuclear energy in achieving net zero goals worldwide. In this context, wanted to implement national projects and strategies to achieve the global goal of tripling nuclear power generation capacity by 2050 (taking 2030 as a reference) and to act to ensure that nuclear power plants are operated in security conditions. This paper examines the potential of Small Modular Reactors (SMRs) in Romania's energy landscape, considering the country's recent commitment to the Net Zero Nuclear Initiative and the goal of tripling nuclear capacity by 2050. The focus is on integrating new nuclear technologies, particularly SMRs, and modernizing existing facilities like the Cernavodă Power Plant. The study also explores the economic benefits, public perception challenges, and the role of European and American expertise in advancing SMR technology. For the first time, using specialized literature and data from public sources, the study aims to analyze the prospects for SMR projects developed in Romania to overcome two essential perspectives: capital costs and public perception in many communities where concerns related to nuclear safety, radioactive waste management, and potential risks associated with nuclear technologies exist.

Design standardisation and seismic protection of SMRs through modular metafoundations

This paper investigates the seismic protection of the Nuward™ small modular reactor (SMR) building, focusing on design loading and beyond design basis earthquake (bDBE) conditions. The study aims to achieve two primary objectives: i) to enhance seismic mitigation of a SMR building under bDBE conditions, through the use of the innovative modular single-layer (SLM) and multi-layer (MLM) metafoundations (MFs); ii) to effectively standardise and harmonise SMR building designs in locations prone to beyond design basis conditions. To accomplish these goals and demonstrate the protective capabilities of the MFs, the study employs non-linear time-history analyses (NLTHAs) for both DBE and bDBE conditions. Along these lines, a reduced-order model was developed from a refined finite element (FE) model of the SMR building using the Craig-Bampton mode synthesis technique. Then, finite locally resonant modular MFs were designed and analysed using NLTHAs. Specifically, physics-based ground motion models (GMMs) were used to generate and select seismic triplets that mimicked DBE and bDBE scenarios for NLTHAs. Successively to achieve improved seismic performance, the optimization of the MFs was pursued by targeting the optimal number of columns, resonator parameters, and unit cell dimensions. Additionally, the deployment of inerters was considered, to significantly reduce the size of the MFs and enable their application in multiple layers for ultra-low frequency attenuation. The overall findings suggest that modular MFs meet seismic protection requirements, and positively contribute to the standardization process of SMR buildings, even in areas characterized by beyond-design seismic conditions.

Study on the coupling effects between reactor coolant system and the internal structure on floor response spectrum of small modular reactor

AbstractAccording to Chinese code and US standard review plan (US SRP), when the equipment and structure satisfy certain decoupling conditions, the seismic analysis of the structure is performed using a decoupling method, where only the mass of the equipment is considered in the structure. The reactor coolant system of small modular reactor (SMR) which is integrated is different from that of PWR, and it is more likely to affect the seismic response of the supporting structure. In this paper, a decoupling model was first constructed based on the decoupling principles in the code. Then, a coupled model is built by connecting the main loop system model with the structure. The floor response spectra of the decoupling model and the coupled model are analyzed separately using ACS SASSI software to investigate the coupling effect. By the comparison of the results, the preliminary conclusions are drawn as follows: the decoupling criteria in code are met for the internal structure and reactor coolant system. For hard rock site, the coupling effect has negligible influence on the in‐structure response spectra (ISRS) for most of the structure except the reactor pit, which shows obvious change in the high‐frequency region. For soft soil site, there is no remarkable influence on the ISRS of the structure even for the reactor pit due to the filter effect of the site to the high‐frequency component in the seismic input. For the site with shear wave velocity greater than 1100 m/s, the influence of couple effect cannot be ignored.

Research on the temperature field of a horizontal reactor coolant pump canned motor

Abstract The temperature of the flywheel and rolling bearing is a key factor in the stability and safety of the canned motor reactor coolant pump(RCP). The horizontal Canned motor reactor coolant pump (HRCP) is the guarantee of the small modular reactor (SMR) security. HRCP is smaller than traditional RCP, The design of heat shield and flywheel cooling channel reduce the temperature of the flywheel and rolling bearing. In order to calculate the cooling performance of the above two structures. Based on the model,a thermal-fluid-solid coupling method has been used to investigate the safety of the HRCP. Results show that the temperature of the water-lubricated rolling bearing is lower than the allowable temperature; but the temperature of the flywheel is too high. In order to reduce the flywheel temperature, the author proposes a new flywheel cooling channel.it is found that this structure has an obvious effect on reducing the flywheel temperature. This structural design provides a reference for the improvement of the canned motor RCP and the optimization of the flywheel design.

Performance analysis of a novel co-generation system integrating a small modular reactor and multiple hydrogen production equipment considering peak shaving

A novel integrated system comprising plasma gasification, small modular reactor (SMR) power generation, pressure swing adsorption (PSA) hydrogen production, and Cu–Cl cycle thermochemical hydrogen generation has been proposed for combined electricity and hydrogen co-production. In this innovative configuration, the high-temperature syngas generated by the plasma gasifier is first cooled by the steam from the SMR power plant. It subsequently undergoes water gas shift and is purified using a PSA unit to yield hydrogen product. Meanwhile, the steam generated by SMR is utilized entirely for power generation during daytime peak hours while during night time off-peak hours, a portion of the steam is diverted to provide heat for the Cu–Cl cycle, thereby facilitating load leveling. A comprehensive assessment of the hybrid system has been conducted from both thermodynamic and economic perspectives. Under two operational modes the efficiency of medical waste-to-energy efficiency reaches 63.75 % (daytime) and 63.58 % (night time), with exergy efficiencies of 45.31 % (daytime) and 44.17 % (night time). Furthermore, the net present value (NPV) of the new design is 81,727.18 k$, dynamic payback period (DPP) of 4.34 years and an internal rate of return (IRR) of 41 %. These results substantiate the feasibility of the design from thermodynamic and economic standpoints.

Investigating the possibility of using a mixture of thorium with different fissile materials as a fuel in TRISO particles for the PBMR-400 reactor

The increasing demand for nuclear reactors as a source of clean energy forced nuclear researchers to search for ways to enhance the safety operation of nuclear reactors. This paper discusses the viability of using different thorium compounds ((233U, Th)O2, (235U, Th)O2, (RGPu, Th)O2) as an accident tolerant fuel/advanced technology fuel (ATF) for Pebble Bed Modular Reactor 400 (PBMR-400). A comprehensive analysis of thorium-based fuel performance was carried out and compared with UO2 to develop a novel nuclear fuel with the capability to tolerate severe accident conditions. The neutronic characteristics such as the infinity multiplication factor, initial heavy metal concentration, RGPu concentration and fission products concentration were analyzed. In addition to, the main safety parameters have been calculated to distinguish the effect of the proposed fuels on them. The thermal spectrum and thermal output power have been visualized to give a good insight view inside the core about the distribution of the heat. In general, the neutronic analysis demonstrated good behavior of the examined thorium-based fuel in the PBMR-400 and especially in the case of (RGPu, Th)O2. PBMR-400 showed excellent performance in incinerating a large amount of reactor-grade plutonium when it was used in a kernel fuel bed.

Analysis of gas-cooled micro modular reactor (MMR) fuel

The gas-cooled micro modular reactor (MMR) is a novel concept with a compact fuel form consisting of thousands of tri-isotropic fuel (TRISO) particles dispersed in a silicon carbide matrix. The MMR fuel has a high volume packing fraction and is horizontally placed within graphite channels. This study demonstrates that the horizontal arrangement of MMR fuel within graphite channels resulted in a non-uniform gap between the fuel and graphite brick, leading to an "off-center" temperature distribution within the fuel, and resulting in differences in TRISO performance even within sub-zones positioned symmetrically in the radial direction. Given the complexity of the fuel structure and the challenges involved in simulation, a multi-scale and multi-physics coupled analysis method of MMR fuel was realized in this work by implementing physical models into the open-source finite element platform MOOSE. Thermal-mechanical analysis and failure analysis within sub-zones of the typical design MMR fuel during normal operation were conducted through simulation. The results indicate that higher-temperature sub-zones exhibit increased internal pressure within TRISO and show greater tensile stress in the Chemical Vapor Deposited Silicon Carbide (CVD-SiC) layer. Regarding fuel failure analysis, this work found limited impact from Pd penetration and kernel migration. Pressure-induced particle failure, closely associated with stress in CVD-SiC, emerges as the primary failure criterion. The probability of fuel failure is relatively low, and interfacial cohesive parameters have an impact on the SiC stress and the fuel failure probability at the highest level.

Integration of very small modular reactors and renewable energy resources in the microgrid

Hybrid microgrids, integrating local energy resources, present a promising but challenging solution, especially in areas with limited or no access to the national grid. Reliable operation of off-grid energy systems necessitates sustainable energy sources, given the intermittent nature of renewables. While fossil fuel diesel generators mitigate risks, they increase carbon emissions. This study assesses the viability of integrating a very small modular renewable energy reactor into a microgrid for replacing conventional diesel generators, substantially curbing greenhouse gas emissions. A comprehensive analysis, including design and economic evaluation, was conducted for an off-grid community microgrid with an annual generation and load of 8.5 GWh and 7.8 GWh, respectively. The proposed microgrid configurations incorporate very small modular reactors, alongside solar, wind, and battery storage systems. MATLAB modeling and simulation across eight cases, accounting for seasonal variations, demonstrate the technical and economic feasibility of case 7. This configuration, integrating modular reactors, photovoltaics, wind turbines, and battery storage, satisfactorily meets load demands. Notably, it boasts a high internal rate of return up to ∼31% and a shorter payback period of around 4 years compared to alternative scenarios.