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| Fig. 1: The floating power station Akademik Lomonosov. (Source: Wikimedia Commons) - This figure dangles. |
The most common way to quantify nuclear power plant size is the maximum power generation the plant can continually produce. This is also how the size categories of nuclear power plants, like Small Modular Reactors (SMRs), are defined. However, there is not a clear definition regarding the size range for a plant to be designated as an SMR. Some sources assert that SMRs are reactors smaller than 10 MW, while others assert that 1600 MW is the maximum power output. [1,2] Seemingly 300 MW is the most common cutoff for the maximum size for SMRs. [3,4] There is also a size category of reactors smaller than SMR called Microreactors. [1] The International Atomic Energy Agency defines microreactors as a nuclear reactor that typically generates no greater than 10 MW of power. [1] Thus, this paper will only be looking at reactors within the most common maximum power generation capacity of SMRs, specifically 10 MW to 300 MW.
Furthermore, to focus on the design constructs specific to SMRs in comparison to other nuclear plant size categories, this paper will only be looking at SMR light-water reactors to make design comparisons simpler. However, there are a multitude of reactor designs being considered for SMRs currently like high temperature gas-cooled, liquid metal-cooled fast neutron spectrum, and molten salt SMRs, this paper will not be going into them. [1] This report will go into 4 total examples of SMRs, 2 examples each of light-water reactor designs for land-based and marine-based reactors.
To briefly discuss SMR deployment, there are currently very few commercial SMR designs that have been deployed in the world. Specifically, as of 2023, there are only 2 SMR being used for commercial power production: the KLT-40S in Pevek of Russian Federation and the HTR-PM in China. [1,5] While the KLT-40S will be discussed in this paper as it is a light-water reactor, the HTR-PM will not since it is a high-temperature gas-cooled reactor meaning the moderator utilized in the reactor is graphite rather than water. [1] The three other SMR designs discussed in this report are at different stages of development within the design stage with current deployment plans either being unknown or years in the future. [1,5,6] Thus this paper is focusing on comprising a few design examples to show the current state of light-water SMR designs while acknowledging that the current designs for not deployed SMRs could change before the reactors are deployed as well as there being a possibility that the designs are never deployed.
Westinghouse SMR is at the higher end of the SMR electrical capacity scale with a capacity of 225 MW. [1,7] This reactor design was developed by Westinghouse Electric Company LLC (USA) based on designs from the AP1000 plant. [1,7] The SMR is an Integral Pressurized Water Reactor meaning the primary circuit components are placed in the reactor vessel eliminating the need for large loop piping decreasing the threat of coolant spillage accidents. [1] The reactor uses UO2 pellets with a fuel enrichment of less than 5%. [1] The reactor is designed to have a refueling cycle of replacing 40% of the core every 2 years and a design life of 60 years. [1] The conceptual design for the reactor is completed but as of 2022, has not been commercially deployed. [1]
The reactor design is 100% modular and the size of the primary components are kept as small as possible to enable transportation and utilization in a wide range of locations and circumstances. [1,7] The plant relies on passive safety features driven by gravity and natural circulation flow rather than being reliant on power systems. [7] In fact, the plant has a 7-day minimum coping time with the loss of offsite power. [1,7] This combined with it modular design makes the plant resilient against natural phenomena hazards and accident scenarios. [1]
The NUWARD is an Integral Pressurized Water Reactor developed by EDF, a multinational electric utility company owned by the government of France. [1] The reactor development entered the Basic Design stage in 2023 with a projected first concrete for the FOAK in France by 2030. [1] This nuclear plant is being developed to supply power to remote municipalities, energy-intensive industrial sites, and grids with limited capacity. [1]
Each NUWARD SMR has an electrical capacity of 170MW though the nuclear plant design includes two reactors for a total power output of 340 MW. [1] The fuel utilized is UO2 pellets with a fuel enrichment of less than 5%. [1] The reactor has a refueling cycle of 2 years with a design life of 60 years. [1] The reactor is also designed to be boron-free so various U-235 enrichments and burnable poisons are used in the fuel. [1] Furthermore, the reactivity is controlled through these solid burnable poisons in tandem with a control rod drive mechanism (CRDM). [1]
Another notable design choice is that the reaction pressure vessels that encompasses each reactor are submerged in a pool filled with water. [1] The reactor also utilizes the components of the Nuclear Steam Supply System, a term meaning a single vessel contains all the main reactor coolant systems in a Pressurize Water Reactor like Control Rod Drive Mechanism (CRDM), Compact plate Steam Generators (CSGs) and pressurizer. [1]
The safety systems approach is primarily passive in the design without the need for any electrical power supply. [1] The reactor is connected to the reactor pool which acts as an internal ultimate heat sink. [1] Through this connection, the SMR is self-reliant and has a coping time of more than 3 days without outside intervention. [1] Between the two submerged reactors is space for a shared spent fuel pool where spent fuel can cool for ten years before being transported to another location. [1]
The KLT-40S is a floating nuclear power plant designed by JSC to provide cogeneration capabilities for power and heat in remote areas without centralized power supplies. [1,6] In May 2020, 2 KLT-40S began commercial operation on the Akademik Lomonosov, a floating nuclear power station. [1,5] (See Fig. 1.)
Each pressurized water reactor has an electrical capacity of 35 MW. [1,5] The fuel utilized is UO2 pellets with a maximum of 18.6% fuel enrichment. [1,5] The reactor has a refueling cycle of 2.5-3 years with a design life of 40 years. [1,5]
The safety features are primarily active, resulting in the processes requiring electricity but being faster in some of the safety procedures. [1] For example, this SMR utilizes a control rod drive mechanism that releases control and emergency control rods into the reactor core in the case of station power loss. So, during an emergency, the rods are driven into the core at a speed of 2 mm/s which is 10-100 times faster than if a rod was driven by gravity. [1] The nuclear and power plant are also both built to be incredibly sturdy to the point the buildings are designed to withstand the crash of an aircraft of 10 tons. [1]
The BANDI-60 was designed by KEPCO E and C (Republic of Korea) for power generation in off-grid and remote areas. [1] It is a compact two-loop pressurized water reactor that has two U-tube type steam generators. [1] It is part of a block-type pressurized water reactor plant meaning the main components of the power plant are directly connected. [1,8] As of 2023, the BANDI-60 is still a conceptual design with KEPCO E and C planning to begin construction in 2030. [1,5]
This pressurized water reactor has an electrical capacity of 60 MW. [1,5] The fuel utilized is UO2 with a maximum of 4.95% fuel enrichment. [1,5,8,9] The reactor has a refueling cycle of 4-5 years with a design life of 60 years. [1,5] The plant is also designed to be soluble boron-free which can provide many advantages like nuclear plant size reduction through simplifying the chemical volume control system, decreasing the amount of liquid radioactive waste, and preventing corrosion from boric acid. [1,8,9]
The BANDI-60 safety system has a rigorous passive system consisting of a Passive Safety Injection System that performs gravity driven safety injection, a Passive Residual Heat Removal System that performs decay heat removal, and a Passive Containment Cooling System that performs condensation and convection through the containment vessel to the ultimate heat sink and refueling water tank. [1]
© Annie Homer. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Advances in Small Modular Reactor Developments, 2022 Edition," International Atomic Energy Agency, September 2022.
[2] "Status of Innovative small and Medium Sized Reactor Designs 2005," International Atomic Energy Agency, IAEA-TECDOC-1485,March 2006.
[3] M. K. Rowiknski, T. J. White and J. Zhao, "Small and Medium Sized Reactors (SMR): A Review of Technology," Renew. Sustain. Energy Rev. 44, 643 (2015).
[4] S. E. Hirdaris et al., "Considerations on the Potential Use of Nuclear Small Modular Reactor (SMR) Technology for Merchant Marine Propulsion," Ocean Eng. 79, 101 (2014).
[5] "Small Modular Reactors For Marine-Based Nuclear Power Plant," International Atomic Energy Agency, November 2023.
[6] S. V. Beliavskii et al., "Effect of Fuel Nuclide Composition on the Fuel Lifetime of Reactor KLT-40S," Nucl. Eng. Des. 360, 110524 (2020).
[7] R. J. Fetterman et al., "An Overview of the Westinghouse Small Modular Reactor," Paper No. SMR2011-6597, ASME 352343, in Proc. ASME 2011 Small Modular Reactor International Symposium (ASME, 2012). p. 75.
[8] D. Kim, J. T. Seo, and H., J. Shim, "Comparison of BANDI-60 Core Designs Using Pyrex Burnable Absorber and Annular Fuel Embedding Gadolinia Wire," Ann. Nucl. Energy 195, 110119 (2024).
[9] D. Kim, H. J. Shim, and J. T. Seo, "Comparison of Core Design Parameters For BANDI-60 Using UO2 ad U-Mo Fuels," Seoul National University, 19 May 22.