Small Modular Reactor (SMR)

Definition and Technical Overview

A Small Modular Reactor (SMR) is a nuclear fission reactor with an electrical output typically below 300 megawatts, designed as a factory-fabricated, transportable module rather than a large custom-built installation. SMRs incorporate advanced safety features including passive cooling systems that function without external power or operator intervention, making them inherently safer than many conventional nuclear plants. Their modular construction allows for serial manufacturing, potentially reducing costs and construction timelines compared to gigawatt-scale reactors.

The defining characteristics of SMRs include compact physical footprint, simplified operations, enhanced safety margins through passive systems, and the flexibility to be deployed in locations unsuitable for conventional nuclear power plants. Multiple SMR designs are under development globally, utilising various reactor types including pressurised water, molten salt, high-temperature gas, and liquid metal cooled designs. The International Atomic Energy Agency (IAEA) has catalogued more than 80 SMR concepts worldwide as of 2026.

Korea's SMR Strategy: Maritime Focus

Korea's approach to SMR technology under K-Moonshot is distinctive in its emphasis on maritime propulsion. While other nations focus primarily on land-based power generation, K-Moonshot Mission 5 targets the development of eco-friendly SMR-powered vessels, leveraging Korea's world-leading shipbuilding industry to create an entirely new category of zero-emission commercial ships.

This strategic choice reflects Korea's dominant position in global shipbuilding. HD Hyundai Heavy Industries, Samsung Heavy Industries, and Hanwha Ocean collectively control approximately 40 percent of the world's commercial shipbuilding order book. The International Maritime Organisation (IMO) has mandated net-zero greenhouse gas emissions from international shipping by approximately 2050, creating massive demand for zero-emission propulsion technologies. Nuclear propulsion, proven over seven decades in naval vessels and icebreakers, offers the energy density and range that battery-electric and hydrogen fuel cell systems cannot match for large ocean-going ships.

HD Hyundai's SMR Programme

HD Hyundai leads Korea's SMR vessel development effort. The company has announced plans to develop a molten salt reactor design optimised for marine installation, with key specifications targeting thermal output of approximately 100 megawatts, sufficient to propel a large container vessel at full speed while eliminating all carbon emissions from propulsion. HD Hyundai's shipbuilding division brings decades of experience integrating complex propulsion systems into commercial vessels, a capability that no dedicated nuclear company possesses.

The company's roadmap envisions prototype reactor design completion by 2028, land-based testing by 2030, and the first sea trials of an SMR-powered vessel by 2032-2033. Korea Nuclear International Cooperation Foundation and the Korea Atomic Energy Research Institute (KAERI) provide regulatory and research support. The project must navigate complex international regulatory frameworks, as the IMO's current rules effectively prohibit commercial nuclear-powered merchant vessels, requiring parallel diplomatic and standards-setting efforts.

Global Context and Competition

Korea is not alone in pursuing SMR technology, but its maritime focus gives it a differentiated position. The United States leads in land-based SMR development, with NuScale Power receiving the first-ever SMR design certification from the US Nuclear Regulatory Commission in 2023, though its first commercial project was subsequently cancelled due to cost overruns. China's HTR-PM, a high-temperature gas-cooled reactor, began commercial operation in December 2023, making it the first operational Generation IV reactor. The United Kingdom has committed over one billion pounds to the Rolls-Royce SMR programme for domestic power generation.

In the maritime sector, competition is emerging but limited. Japan's ClassNK has developed classification guidelines for nuclear-powered merchant ships. China's CNNC has proposed floating nuclear power platforms for offshore applications. However, no country has combined Korea's depth of nuclear engineering capability with its shipbuilding industrial base, a convergence that the Ministry of Science and ICT views as a potential source of sustained competitive advantage in a market projected to reach $100 billion annually by 2040.

Technical Challenges and Safety

Developing SMRs for marine applications presents unique engineering challenges beyond those faced by land-based installations. Marine reactors must withstand constant vibration, corrosive saltwater environments, extreme weather conditions, and the dynamic loading forces of ocean transit. Reactor containment structures must be engineered to remain intact during collision scenarios, grounding events, and severe storms. Fuel management and spent fuel handling in port environments require entirely new protocols and infrastructure.

Safety validation for marine SMRs demands demonstration that passive safety systems function reliably under all plausible maritime scenarios, including loss of coolant accidents during high sea states and reactor behaviour during severe ship motions. Korea's nuclear regulatory framework, administered by the Nuclear Safety and Security Commission (NSSC), will require adaptation to address these maritime-specific safety cases. The regulatory pathway itself is a major component of Mission 5, as international acceptance depends on Korea establishing credible safety standards.

Economic and Environmental Implications

The economic case for SMR vessels centres on long-term fuel cost advantages and emissions compliance. A single transoceanic voyage by a large container ship consumes approximately 150 tonnes of heavy fuel oil per day. An SMR-powered vessel would operate for years between refuelling, eliminating fuel costs that can exceed $50,000 per day at current prices. The capital cost premium of nuclear propulsion, while substantial, could be recovered over the 25-30 year operating life of a commercial vessel.

From Korea's investment perspective, SMR vessels represent a potentially transformative export product. If Korea can demonstrate safe, commercially viable nuclear-powered merchant ships before competitors, it would establish a first-mover advantage in a market driven by mandatory decarbonisation regulations. The convergence of Korea's nuclear technology expertise and shipbuilding dominance makes this mission one of the most distinctive elements of the entire K-Moonshot programme.