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.

Small modular reactors (SMRs) are getting attention as an alternative to fossil fuel power stations due to versatile application and carbon dioxide reduction. Although various types of advanced reactors are being developed, water-cooled SMR will be first deployed on a commercial scale. The International Atomic Energy Agency (IAEA) and regulatory bodies are trying to identify safeguards issues of water-cooled SMRs as the first priority. IAEA begins to develop a safeguards plan by asking for the facility’s specification in a given format, a design information questionnaire (DIQ). Then, IAEA periodically performs safeguards activities such as design information verification (DIV) and physical inventory verification (PIV). In this sense, we utilize research and power reactor DIQ for water-cooled SMRs (NuScale, SMART, i-SMR and KLT-40S). Most of the questions are answered with open information. For undisclosed answers, pressurized water reactor (PWR) features are described. Safeguards issues in water-cooled SMR originate from core modularization. As the nuclear material flows are diversified, the number of safeguards measure will be increased while staff are reduced in SMRs. Instrumentation for safeguards should be developed to reduce worker’s fatigue level. Intensive arrangement of fuel assemblies may also need unique devices to secure their visibility or detectability. A transparent floor with a surveillance system or advanced Cherenkov viewing device may be adopted to enhance containment and surveillance. Meanwhile, some questions could be more elaborate regarding safeguards. First, question #38 cannot confirm the time of occurrence of weapon-grade plutonium for reactor operation. Second, the answers in questions #46 and #49 are primitive to identify a place to generate an undeclared fissile material. Therefore, the current DIQ should be revised to get a detailed burnup report and spatial distribution of neutron flux.

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.