Small Modular Reactors Designs Research Articles

TSUNAMI Analyses of the Similarity and Applicability of Zero Energy Deuterium 2 Critical Experiments for Reactor Physics Code Benchmarking for a Pressurized Water Reactor Small Modular Reactor Design Concept

Abstract This paper presents the findings of studies conducted at Canadian Nuclear Laboratories (CNL) to support the development of small modular reactor (SMR) designs. The primary focus of this research was to evaluate the suitability of the zero energy deuterium 2 (ZED-2) critical facility in replicating the reactor physics environment for a pressurized water reactor small modular reactor (PWR-SMR) design concept through similarity and nuclear data sensitivity studies, using the TSUNAMI code suite. It was found that previous ZED-2 experiments would be quite promising for application to a PWR-SMR design. Further similarity and sensitivity studies of hypothetical mixed-lattice substitution experiments, where PWR-SMR fuel assemblies were placed into a substitution region of the ZED-2 critical facility demonstrated improved similarity. Subsequent analyses focused on the impacts of dissolved Gadolinium (Gd) and boron (B) neutron absorbers, suggesting the feasibility of using future ZED-2 experiments to more closely replicate PWR-SMR reactor physics behavior. Building on these initial findings, the design for PWR-SMR fuel assembly substitution experiments in the ZED-2 facility were explored further. These hypothetical experiments feature water-cooled PWR-type fuel assemblies inside a shroud, surrounded by heavy-water-moderated CANdu FLEXible, Low Enriched Uranium, Recovered Uranium (CANFLEX-LEU/CANFLEX-RU) fuel channels. Similarity and sensitivity studies indicate a very high level of similarity of these experiments for PWR-SMR design applications.

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.

Analysis of heat-loss mechanisms with various gases associated with the surface emissivity of a metal containment vessel in a water-cooled small modular reactor

In various small modular reactor (SMR) designs currently under development, the conventional concrete containment building has been replaced by a metal containment vessel (MCV). In these systems, the gap between the MCV and the reactor pressure vessel is filled with gas or vacuumed weakly, effectively suppressing conduction and convection heat transfer. However, thermal radiation remains the major mode of heat transfer during normal operation. The objective of this study was to investigate the heat-transfer mechanisms in integral pressurized water reactor (IPWR)-type SMRs under various gas-filled conditions using computational fluid dynamics. The use of thermal radiation shielding (TRS) with a much lower emissivity material than the MCV surface was also evaluated. The results showed that thermal radiation was always the dominant contributor to heat loss (48–97%), while the conjugated effects of the gas candidates on natural convection and thermal radiation varied depending on their thermal and radiative properties, including absorption coefficient. The TRS showed an excellent insulation performance, with a reduction in the total heat loss of 56–70% under the relatively low temperatures of the IPWR system, except for carbon dioxide (13%). Consequently, TRS can be utilized to enhance the thermal efficiency of SMR designs by suppressing the heat loss through the MCV.

Evaluating direct vessel injection accident-event progression of AP1000 and key figures of merit to support the design and development of water-cooled small modular reactors

The passive safety systems (PSSs) within water-cooled reactors are meticulously engineered to function autonomously, requiring no external power source or manual intervention. They depend exclusively on inherent natural forces and the fundamental principles of reactor physics, such as gravity, natural convection, and phase changes, to manage, alleviate, and avert the release of radioactive materials into the environment during accident scenarios like a loss-of-coolant accident (LOCA). PSSs are already integrated into such operating commercial reactors as the Advanced Pressurized Reactor-1000 MWe (AP1000) and the Water-Water Energetic Reactor-1200 MWe (WWER-1200) are adopted in most of the upcoming small modular reactor (SMR) designs. Examples of water-cooled SMR PSSs are the passive emergency core-cooling system (ECCS), passive containment cooling system (PCCS), and passive decay-heat removal system, the designs of which vary based on reactor system-design requirements. However, understanding the accident-event progression and phases of a LOCA is pivotal for adopting a specific PSS for a new SMR design. This study covers the accident-event progression for direct vessel injection (DVI) small-break loss-of-coolant accident (SB-LOCA), associated physics phenomena, knowledge gaps, and important figures of merit (FOMs) that may need to be evaluated and assessed to validate thermal-hydraulics models with an available experimental dataset to support new SMR design and development.

Design and construction of fluid-to-fluid scaled-down small modular reactor platform: As a testbed for the nuclear-based hydrogen production

This paper presents the construction results and design of the UNIST Reactor Innovation platform for small modular reactors as a versatile testbed for exploring innovative technologies. The platform uses simulant fluids to simulate the thermal-hydraulic behavior of a reference small modular reactor design, allowing for cost-effective design modifications. Scaling analysis results for single and two-phase natural circulation flows are outlined based on the three-level scaling methodology. The platform's capability to simulate natural circulation behavior was validated through performance calculations using the 1-D system thermal-hydraulic code-based calculation. The strategies for evaluating cutting-edge technologies, such as the integration of a solid oxide electrolysis cell for hydrogen production into a small modular reactor, are presented. To overcome experimental limitations, the hardware-in-the-loop technique is proposed as an alternative, enabling real-time simulation of physical phenomena that cannot be implemented within the experimental facility's hardware. Overall, the proposed versatile innovation platform is expected to provide valuable insights for advancing research in the field of small modular reactors and nuclear-based hydrogen production.

NUWARD SMR safety approach and licensing objectives for international deployment

Drawing on the deep experience and understanding of the principles of nuclear safety, as well as many years of nuclear power plant design and operation, the EDF led NUWARD SMR Project is developing a design for a Small Modular Reactor (SMR) of 340 MWe composed of two 170 MWe independent units, that will supplement the offering of high-output nuclear reactors, especially in response to specific needs such as replacement of fossil-fuelled power plants. NUWARD SMR is a mix of proven and innovative design features that will make it more commercially competitive, while integrating safety features that comply with the highest international standards. Following the principles of redundancy and diversity and rigorous application of Defence in Depth (DID), with an international view on nuclear safety licensing, the Project also incorporates new safety approaches into its design development.The NUWARD SMR Project has been in development for a number of years, it entered conceptual design formally in mid-2019 and entered Basic Design in 2023. The objective of the concept design phase was to confirm the project technological choices and to define the first design configuration of the NUWARD SMR product, to document it, in order to launch pre-licensing with the French Safety Authority (ASN) and to define its estimated cost and its subsequent development and construction schedules. As a delivery milestone the Safety Options file (called the Dossier d’Options de Sûreté (DOS)) has been submitted to ASN in July 2023 for their opinion.An integral part of the NUWARD SMR Project, is not only to deliver a design suitable for France and to satisfy French regulation, but to develop a product suitable and indeed desirable, for the international market, with a first focus in Europe. In order to achieve its objectives and realise its market potential, the NUWARD SMR Project needs to define and realise its safety approach within an international environment and that is the key subject of this paper. The following paper:• Summarises the foundation principles and technological background which underpin the design;•Contextualises the key design features with regard to the international safety regulatory framework with particular emphasis on innovative passive safety aspects;•Illustrates the Project activities in preparation for first licensing in France, and also a wider international view via the ASN led Joint Early Review of the NUWARD SMR design, including Finnish and Czech Republic regulators, recently joined by the Swedish, Polish and Dutch regulators;•Articulates the collaborative approach to design development from involvement with the Project partners (the Commissariat à l’énergie atomique et aux énergies alternatives (CEA), Naval Group, TechnicAtome, Framatome and Tractebel) to the establishment of the International NUWARD Advisory Board (INAB), to gain greater international insight and advice;•Concludes with the focus on next steps into detailed design development, standardisation of the design and its simplification to enhance its commercial competitiveness in a context of further harmonisation of the nuclear safety and licensing requirements and aspirations.

Spanish research related to SMRs projects

Small modular reactors (SMRs) are advanced nuclear reactors with a power capacity of up to 300 MW(e) per unit. SMRs encompass a variety of reactor technologies including light water reactors, high temperature gas reactors, molten salt reactors, liquid metal cooled fast reactors, and heat pipe technology-based reactors. The research and design of these diverse SMR types require a broad set of technological capabilities related to nuclear engineering and safety. Within this context, this article attempts to assess the current state of research and technological progress achieved by the Spanish research groups and companies. The results reveal a significant level of maturity among these groups and companies in various domains such as neutronic analysis, thermal hydraulic analysis, the improvement of models related to severe accident scenarios and an active involvement in the design of novel SMR.

An Approach for Integration of User Requirement and Anthropometry Data in The Process Design of Reactor Main Control Room

The construction of a Nuclear Power Plant (NPP) using Small Modular Reactor (SMR) technology is an interesting scheme to support Net-Zero Carbon Emission. The SMR design is an advanced generation reactor with high safety and utilization features, especially the electricity needed and industry. Its modular size can also be applied to remote areas with lower construction costs compared to other types of power plants. Considering the geographical location and territory of Indonesia which is an archipelagic country, this type of reactor is suitable for application in Indonesia. To ensure safety and increase mastery of technology, it is necessary to create a simulator to support this program. Nonetheless, specific regulations govern human-machine interactions (HMI) which is covering the nuclear reactor simulators in Indonesia is not yet available. The research carried out is a review of the regulations that have been implemented in other countries, then provides a choice of operator condition designs, which are adjusted to the average size of Indonesian by considering anthropometric aspects and ergonomic aspects.

Performance analysis of heat pipe-based passive in-core decay heat removal system for the small modular reactor design with MARS-KS code

This study explores the effectiveness of using Passive IN-core Cooling Systems (PINCs) for Small Modular Reactors (SMRs) during Station Blackout (SBO) conditions. An introduction to the concept of PINCs, along with strategies for their application to SMRs with design modifications, is presented. Transient safety analysis was conducted using the MARS-KS code on NuScale SMR designs that incorporate PINCs. The findings demonstrate that PINCs can serve as an additional means for decay heat removal in addition to the existing safety systems. The feasibility of PINCs as an effective means for indefinite cooling of SMRs was affirmed under SBO conditions, even in the absence of DHRS and ECCS operations. The PINCs system demonstrates its potential as an effective means for pressure reduction and long-term or indefinite cooling in SMRs under extreme conditions such as SBO.

Bibliometric Review and Technical Summary of PWR Small Modular Reactors

Given the real problem of climate change and the consequent need to reduce greenhouse gas emissions, nuclear energy can be considered a real technological option in the absence of a technology that can supply the population with sufficient electrical energy in a sustainable way. The research and development advances of new nuclear reactor designs are evident in the case of Small Modular Reactor (SMR) technology. Two goals are clear in such a technology: (i) reducing onsite construction costs and time; (ii) promoting economic efficiency through the mass production of nuclear reactors. In view of the interest generated by this technology, a technical summary of PWR-SMR design is included in this paper, utilizing the scientific method based on: (i) a bibliometric review of scientific publications related to SMRs; and (ii) a technical analysis of aspects of the different PWR-SMR designs. The results obtained in the present research show a growing interest on the part of the scientific community in research on PWR reactors integrated within SMR designs. Few countries are doing research in this area; however, those that are doing so have achieved greater technological advances in their designs, resulting in greater technological variety and a higher degree of maturity.

Seismic resilience assessment of Small Modular Reactors by a Three-loop Monte Carlo Simulation

We develop a three-loop Monte Carlo Simulation (MCS) framework for the seismic resilience assessment of Small Modular Reactors (SMRs), embedding Probabilistic Seismic Hazard Analysis (PSHA), seismic fragility evaluation and multiple SMR units accident sequence analysis. A set of metrics are computed to capture different aspects of SMR resilience to earthquakes, specifically the ability to withstand seismic disruption, mitigate consequences and restore normal operation. The MCS framework allows accounting for the aleatory and epistemic uncertainties of the PSHA and fragility parameters. An application is given with regards to an advanced Nuclear Power Plant (aNPP) consisting of four reactor units of NuScale SMR design. A comparison is made to a conventional NPP (cNPP), i.e., a typical large reactor of equivalent generation capacity. Both plants are fictitiously located on the Garigliano nuclear site (southern Italy). The results show that resilient features of SMRs overcome cNPPs in terms of post-accident scenario mitigation and restoration capabilities.

Study on the costs and benefits of establishing a unified regulatory guidance for emergency preparedness of small modular reactors in China

Small modular reactors (SMRs) are rapidly developed worldwide in recent years for their potential extensive applications. China is very active in promoting SMR design and construction. However, the current emergency preparedness (EP) guidance in China is developed based on the characteristics of large water-cooled reactors, and they are only partially applicable to SMRs. In our previous work, we have fully demonstrated from a technical perspective that it is feasible for China to establish a unified EP framework for all SMR designs based on the dose and consequence of an accident spectrum. Therefore, this paper will comprehensively discuss the costs and benefits of establishing a unified EP guidance for all SMR designs in China. Uncertainty analysis is also conducted for variables with great uncertainty. Through the study in this paper, it can be concluded that developing a new unified EP regulatory guidance for all SMR designs in China is cost beneficial in most cases. In addition, it will also bring other benefits that are hard to be quantified, such as the consistency of supervision, the clarity of the EP plan, and the improved engagement of all stakeholders during SMR development. In a word, it would always be beneficial to establish a new unified EP regulatory guidance for all SMR designs in the long term.

Unique safety features and licensing requirements of the NuScale small modular reactor

Small modular reactors (SMR) offer a novel approach to the construction and operation of nuclear power plants. The NuScale VOYGR™ plant uses a simplified SMR design that is based on proven light-water reactor technology with substantial improvements in nuclear safety. It consists of a 250 MWt reactor core housed with other primary system components in an integral reactor pressure vessel surrounded by a steel containment vessel, all of which is immersed in a large pool of water that also serves as the ultimate heat sink. At the core of the NuScale safety case are three primary safety systems: the decay heat removal system, the emergency core cooling system, and the containment. The ability of the NuScale Power Module (NPM) passive safety systems to remove core decay heat for an unlimited duration is demonstrated through analysis of a beyond-design-basis extended loss of AC power with no replenishment of water to the ultimate heat sink or operator actions. The NuScale methodology to evaluate an indefinite loss of AC power uses the proprietary NRELAP5 systems analysis computer code. Analysis results show that the reactor coolant system liquid level above the core is maintained and that containment pressure remains below the vessel design pressure. Once full passive air cooling is established, containment pressure and temperature will decrease over time with decreasing core decay heat. NuScale received standard design approval in September 2020 and design certification in January 2023 for its 50 MWe NPM configured as a 12 module plant. NuScale is currently seeking standard design approval to increase its core power to 250 MWt, nominally 77 MWe per module, in a 6-module plant (VOYGR™-6) configuration. The high-level safety of NuScale’s SMR technology is foundational to a new standard of nuclear power plant resilience.

Small Modular Reactors Licensing Process Based on BEPU Approach: Status and Perspective

The competitiveness of small modular reactors (SMRs) has been planned based on design simplification, short construction time, passive safety systems, and enabling self-financing by ramp-up construction. Due to the global energy challenges, SMRs have received pervasive attention from a wide range of researchers, designers, developers, stakeholders, and customers. Besides the many advantages related to the design of SMRs, there are challenges ahead of these reactors. SMR licensing is one of the most critical challenges in the front deployment of these reactors. This challenge stems from innovations in SMR designs and systems, such as modularity or deployment for desalination, energy storage, hydrogen production, process heat, and district heating. Due to the lack of experimental data and technical knowledge, the licensing challenges for non-water coolant SMRs are more complicated. Nearly all previous generation reactor licenses were based on conservative analysis while the decision-making methods based on best-estimate and realistic approaches have received more attention in recent years. Thus, the method known as the best estimate plus uncertainty (BEPU) approach is selected for licensing in some cases. At this time, using the BEPU approach in licensing for conventional NPPs is a mature technology and ready for industrial application. Nevertheless, because most previous reactors were licensed based on conservative methods, developers and even regulatory bodies resist re-assessments based on the BEPU approach, while using the choice of conventional conservative methods is a type of roll-back for next-generation SMRs. Thus, this work reviews the BEPU approach and clarifies the possibility of using this approach in the licensing process of SMRs. The lack of experimental data and tight coupling of phenomena along with uncertainty quantification are the main challenges ahead of using BEPU in the licensing process of SMRs.

Measurements of natural convection heat transfer of a helical coil varying the pitch and the turn

A helical coil is gaining interest as the part of a compact heat exchanger since it allows large heat transfer area. Many small modular reactor designs adopt the helical coil steam generator. We measured the local and total heat transfers of the helical coil using ring bundles to confirm the influences of pitches and turns. The pitch to coil diameter ratio was varied from 1.08 to 3.97 and the turns from 2 to 12, with the Ra of 3.63 × 107. Based on the analogy between heat and mass transfers, mass transfer experiments were performed replacing heat transfer ones. For a small pitch, the heated plume from the lower ring provides preheated plume to the upper ring, resulting in an impaired heat transfer. However, for a large pitch, initial velocity is provided, enhancing the heat transfer. The comprehensive heat transfer influences also depend on the coil turns. The measurements of total heat transfer showed the peak at around the pitch to coil diameter ratio range from 1.50 to 2.02 regardless of the number of coil turns.

Scaling challenges in small modular reactor

The small modular reactor (SMR) has become a popular reactor design concept in recent years. Many regulatory authorities are evaluating a plethora of license applications related to SMRs. One important step of the reactor design is the prototype computer model assessment, and scaling is indispensable toward developing meaningful assessment data. In SMR scaling, new challenges may rise due to compact layout and unique thermal hydraulic phenomena. These phenomena may be greatly distorted or may not even be reproducible at all in the test facility. Therefore, investigation of these phenomena is needed to ensure figures of merit are adequately preserved with minimum distortion. In this paper, some phenomena were highlighted to understand the complexity. An early SMR design - the Multi-Application Small Light Water Reactor (MASLWR) is used to illustrate the scaling of these phenomena.

Analysis of small modular reactor technologies and socio-economic aspects of their application in the Russian Arctic in the era of digital transformation

Small modular reactor technologies and social, economic, and technological aspects of their application in the Russian Arctic are considered in the article. An overview of the key factors influencing an implementation of small modular reactor plants in remote regions with a decentralized power grid is presented. The main directions of small modular reactor design activities of the key Russian centers of atomic research and development are given. An overview of current Russian small modular reactor technologies including pressurized water reactors, boiling water reactors, reactors installed on floating nuclear power plants, high-temperature gas-cooled reactors, and liquid metal cooled reactor is conducted. Economic, social, ecological, and digital aspects of applications of small modular reactor in the Russian Arctic are considered. A detailed survey of areas of small modular reactor application including extractive, processing, industrial energy-intensive facilities, and power and heat supply of cities is also given. The importance of digital twins of small modular as an essential element in the development and maintenance of complex engineering products and industrial facilities throughout the entire life cycle is discussed in the article. Conclusions about key advantages and prospects of an application of small modular reactors in the Russian Arctic are made.

Малые модульные ядерные реакторы: перспективы развития

The need for deep reduction of the greenhouse gases emissions (methane and carbon dioxide) in the atmosphere in order to preserve the global climate amid the growth of electricity production worldwide to meet mankind’s energy needs has stimulated the transfer to the use of energy sources that exclude such emissions. There is an increasing interest to exploitation of renewable energy sources – hydropower, solar and wind power, as well as nuclear power, especially the development of innovative nuclear power. The latter refers to nuclear reactors in which the configuration of systems, coolants, fuels and operating conditions are radically different from traditional reactors. Among promising innovations in the nuclear sector is the concept of small modular reactors (SMRs) whose unique characteristics in terms of enhanced safety, transport mobility, efficiency and economy create favorable conditions for investment in projects to develop them. A number of countries including Argentina, Canada, China, Russia, South Korea and the United States of America are actively working on innovation nuclear power development, and currently more than 70 advanced commercial SMR designs are being built around the world, with the first prototypes to be deployed in the near future or already deployed. However, the construction of a next-generation nuclear power is more than just solving technological problems. Economical factors, primarily the cost of electricity generation compared to renewable energy, will have a significant impact on the development and employment of SMR technology. There is also an export competition among suppliers in the global nuclear technology market, and there are geopolitical issues, including global security and non-proliferation concerns.

Comparison of two methods for assessment of the rod positioning uncertainty and consequences on the evaluation of correlation factors

In this paper two major families of methods to deal with the assessment of the rod positioning uncertainty in a lattice are tested: a traditional one described in the International Handbook of Evaluated Criticality Safety Benchmark Experiments (IHECSBE) Handbook and the other one consisting in sampling the position of rods with Monte Carlo techniques (ISO Uncertainty Guidelines). They are applied on a benchmark with tight-packed lattice of UO2 rods that is sensitive to the rod positioning as it is clearly under-moderated. It is shown that the choice of the method has a great impact on the propagated uncertainty, the traditional one leading to a significant overestimation of the overall uncertainty and can also contribute to a bias in the correlation factors that are used for assessing biases due to nuclear data using GLLSM methodologies. The paper briefly describes the tight-packed lattice experimental program performed at the Valduc Research Centre, which is at the origin of these concerns. Then it proposes a simple model on which to apply simulations of rod positioning to be performed with MORET 5 Monte Carlo code using the Prométhée tool. Results demonstrate that use of Monte Carlo methodologies provide more realistic uncertainty estimates in fuel pitch that are consistent with repeatability/reproducibility experiments. The current comparisons use light water reactor systems, which is directly relevant to some small modular reactor designs. However, accurate prediction and estimate of uncertainties in pitch for advanced reactor systems is also relevant. The application of unrealistic uncertainty analysis methods can incur larger margins in advanced reactor design, safety, and operation than are necessary.

Analysis of BDBA sequences in a generic IRIS reactor using ASTEC code

Integral Severe Accident (SA) codes are aimed at providing an exhaustive coverage of all the main phenomena taking place in a core melt accident. Today, these deterministic codes have reached a high level of maturity for the simulation of operating reactors and the nuclear technical community is starting to extend their applicability to advanced reactor designs, as Small Modular Reactor (SMR). In the framework of the NUGENIA TA-2 ASCOM (ASTEC COMmunity) collaborative project, a generic input-deck based on the IRIS design has been developed for the ASTEC code. The generic SMR ASTEC model has been already proved able to simulate the main thermal–hydraulic phenomena driving the passive mitigation of a SBLOCA in Design Basis Accident (DBA) conditions. The same initiator event, regarding the guillotine break of a Direct Vessel Injection (DVI) line, will be assumed for the simulation of beyond-design scenarios by considering the unavailability of selected passive safety systems. The results of the ASTEC simulations of four Beyond Design Basis Accidents (BDBAs) (study carried out with ASTEC V2.2, IRSN all rights reserved, [2021]) will be analyzed and discussed against the reference DBA sequence in the present paper. This study is aimed at proving the first insights about the capability of the ASTEC model of a generic IRIS reactor to be used in BDBA and in SA analyses, if significant core degradation takes place. In addition, it characterizes the role played by each safety system in SMR passive mitigation strategy and give the possibility to characterize the phenomenologies specific of SMR designs.