The initial development plans for the six reactor designs, soon after the release of Generation IV International Forum (GIF) TRM in 2002, were characterized by high ambition [1]. Specifically, the sodium-cooled fast reactor (SFR) and very-high temperature reactor (VHTR) gained significant attention and were expected to reach the validation stage by the 2020s, with commercial viability projected for the 2030s. However, these projections have been unrealized because of various factors. The development of reactor designs by the GIF was supposed to be influenced by events such as the 2008 global financial crisis, 2011 Fukushima accident [2, 3], discovery of extensive shale oil reserves in the United States, and overly ambitious technological targets. Consequently, the momentum for VHTR development reduced significantly. In this context, the aims of this study were to compare and analyze the development progress of the six Gen IV reactor designs over the past 20 years, based on the GIF roadmaps published in 2002 and 2014. The primary focus was to examine the prospects for the reactor designs in relation to spent nuclear fuel burning in conjunction with small modular reactor (SMR), including molten salt reactor (MSR), which is expected to have spent nuclear fuel management potential.

Recently, more than 70 SMRs have been developed around the world due to their modularity, flexibility, and miniaturization. An innovative SMR (i-SMR) is also being developed in Korea, and operators are planning to apply for a Standard Design Approval (SDA) in 2026 after completing the standard design. Accordingly, regulatory organizations are conducting R&D on regulatory requirements and guidelines for systematic SMR standard design review by referring to IAEA and NRC cases. In terms of security, SMRs are expected to undergo many changes not only in terms of physical security through security systems, security areas, and vital equipments, but also in terms of cybersecurity through new digital technologies, remote monitoring, and automated operation. Accordingly, the IAEA Fundamental Safety Principles (SF-1) require operators to improve the safety of nuclear facilities by considering security requirements, access control requirements, and the results of operational impact assessments based on threats from the design and construction stages. Similarly, the U.S. nuclear regulatory body (NRC) has confirmed the status of security assessment and design considering design basis threats (DBTs) in the NuScale standard design review process, and the Canadian nuclear regulatory body (CNSC) has revised security regulatory guidelines and applied them to the SMR standard design review. Among these various activities related to SMR security, this paper analyzes the major changes in the cybersecurity regulatory guidelines for SMRs recently revised by the CNSC, the Canadian nuclear regulatory body. Compared to the previous guidelines, the Defensive Cybersecurity Architecture (DCSA), including external logical access control, security level and zone communication requirements, verification and validation (V&V) activities during development phases, and system & service acquisition security requirements have been added. Other changes, such as the cyber incident response program, will be analyzed and compared. Through the revised regulatory guidelines, the CNSC has divided cybersecurity levels into four (High, Moderate, Low, and Business), strictly prohibiting remote access to High and Moderate levels, and allowing remote access to Low levels only for maintenance purposes. In addition, the paper will analyze the detailed revisions, such as prohibiting access to the High level from lower levels and allowing only handshaking signals from the Low level to the Moderate level.

In addition to Korea, various countries such as the United States, the United Kingdom, France, and China are designing small module-type reactors. In particular, a small modular reactor is the power of 300 MWe or less, in which the main equipment constituting the nuclear reactor is integrated into a single container. Depending on the purpose, small modular reactors are being developed to help daily life such as power, heating supply, and seawater desalination, or for power supply such as icebreakers, nuclear submarines, and spacecraft propellants. Small modular reactors are classified according to form. It can be classified into light-water reactors/ pressurized light-water reactors based on technology proven in commercial reactors, and non-lightwater reactors based on fuel and coolant type such as Sodium-cooled Fast Reactor, High temperature gas-cooled reactor, Very high temperature reactor and Moltenn salt reactor. SMRs, which are designed for various purposes, have the biggest difference from commercial nuclear reactors. The size of SMRs is as small as 1/5 of that of the commercial reactors. Several modules may be installed to generate the same power as commercial reactors. Because of the individually operation for each module, load follow is possible. Also, The reactor can be cooled by natural convection because the size is small enough. It is manufactured as a module, the construction period can be reduced. Depending on the characteristics of these SMRs, application for safeguards is considered. There are many things to consider in terms of safeguards. Therefore, it is IAEA inspection or other approaches for SMRs installed and remotely operated in isolated areas, data integrity for remote monitoring equipment to prevent the diversion of nuclear materials, verification method and material accountancy and control for new fuel types and reactors. Since SMR is more compact and technical intensive, safeguards should be considered at the design stage so that safeguards can be efficiently and effectively implemented, which is called the Safeguards by design (SBD) in the IAEA. In this paper, according to the characteristics of SMR, we will analyze the advantages/disadvantages from the point of view of safeguards and explain what should be considered.