energies Review Integral PWR-Type Small Modular Reactor Developmental Status, Design Characteristics and Passive Features: A Review Chireuding Zeliang, Yi Mi * , Akira Tokuhiro, Lixuan Lu and Aleksey Rezvoi Faculty of Energy Systems and Nuclear Science, University of Ontario Institute of Technology, Oshawa, ON L1H 7K4, Canada; [email protected] (C.Z.); [email protected] (A.T.); [email protected] (L.L.); [email protected] (A.R.) * Correspondence: [email protected]; Tel.: +1-905-924-2741 Received: 5 March 2020; Accepted: 1 June 2020; Published: 5 June 2020 Abstract: In recent years, the trend in small modular reactor (SMR) technology development has been towards the water-cooled integral pressurized water reactor (iPWR) type. The innovative and unique characteristics of iPWR-type SMRs provide an enhanced safety margin, and thus offer the potential to expand the use of safe, clean, and reliable nuclear energy to a broad range of energy applications. Currently in the world, there are about eleven (11) iPWR-type SMRs concepts and designs that are in various phases of development: under construction, licensed or in the licensing review process, the development phase, and conceptual design phase. Lack of national and/or internatonal comparative framework for safety in SMR design, as well as the proprietary nature of designs introduces non-uniformity and uncertainties in regulatory review. That said, the major primary reactor coolant system components, such as the steam generator (SG), pressurizer (PRZ), and control rod drive mechanism (CRDM) are integrated within the reactor pressure vessel (RPV) to inherently eliminate or minimize potential accident initiators, such as LB-loss of coolant accidents (LOCAs). This paper presents the design status, innovative features and characteristics of iPWR-type SMRs. We delineate the common technology trends, and highlight the key features of each design. These reactor concepts exploit natural physical laws such as gravity to achieve the safety functions with high level of margin and reliability. In fact, many SMR designs employ passive safety systems (PSS) to meet the evolving stringent regulatory requirements, and the extended consideration for severe accidents. A generic classification of PSS is provided. We constrain our discussion to the decay heat removal system, safety injection system, reactor depressurization system, and containment system. A review and comparative assessment of these passive features in each iPWR-type SMR design is considered, and we underline how it maybe more advantageous to employ passive systems in SMRs in contrast to conventional reactor designs. Keywords: small modular reactors; integrated pressurized water reactors; passive safety systems 1. Introduction The pursuit of the development and deployment of small modular reactors (SMRs) is a persistent and global phenomenon with widespread interest from technology developers, Research and Development (R&D) organizations and potential users. Motivations in the development of SMR technology inlcudes: meeting the need for flexible power generation for wider range of users and applications; siting flexibility; options for remote and off-grid application; inherent and enhanced safety features; and the potential for synergetic energy systems. The International Atomic Energy Agency (IAEA) defines small modular reactors as, “advanced nuclear reactors that produce equivalent Energies 2020, 13, 2898; doi:10.3390/en13112898 www.mdpi.com/journal/energies Energies 2020, 1311, 2898x FOR PEER REVIEW 2 of 22 transportable to utilities for installation as demand arises” [1,2]. Many SMRs are envisioned for use inelectric niche power electricity of up or to energy 300 MW(e), markets and arewhere designed large tonuclear be built power in factories plants and are transportablenot feasible, toincluding utilities smallerfor installation grid an asd footprint demand arises”application [1,2].s, Manyreplacement SMRs areof retiring envisioned fossil for fuel use plants, in niche and electricity industrial or processenergy marketsheat applications where large such nuclear as desalination power plants and are hydrogen not feasible, production including [3 smaller,4]. Thus, grid SMRs and footprintoffer the potentialapplications, to expand replacement the use of retiringof safe, fossil peaceful, fuel plants, and reliable and industrial nuclear process energy heat to a applications broad range such of customersas desalination and energy and hydrogen applications. production This, in [3 turn,4]. 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A wegeneric underline overview, that passivean explanantion safety systems of the (PSSs)need for is thisranked technology as the second, and broad most classification important impediment of PSSs based [1]. on In class, fact, thisoperating paper mecha is motivatednism, and by thefunctions results, arepresented provided. in Figure 1. A generic overview, an explanantion of the need for this technology, and broad classification of PSSs based on class, operating mechanism, and functions, are provided. Figure 1. Average ranking of identified challenges for design development and deployment [1]. ReproducedFigure 1. Average from [1], ranking IAEA: 2016.of identified challenges for design development and deployment [1]. Reproduced from [1], IAEA: 2016. 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