Specific Legal and Technical Aspects of Military Impacts on Ukraine’s Nuclear Power Plants

Abstract

This paper presents an analysis of selected legal and technical aspects of nuclear power plant (NPP) safety under conditions of war, based on the case of Ukraine. The 2022 military aggression of the Russian Federation against Ukraine represents the first documented instance in which operating NPPs were subjected to sustained and direct military action. This included the armed occupation of nuclear facilities at the Chornobyl and Zaporizhzhia NPP sites, creating unprecedented risks to civilian nuclear infrastructure. These events challenged all pillars of the international 3S framework — nuclear safety, nuclear security and nuclear safeguards — exposing vulnerabilities not previously encountered at this scale. From a legal perspective, the paper examines the incompatibility of these actions with international humanitarian law, which affords nuclear power plants special protection as installations containing “dangerous forces”. Although legal norms explicitly prohibit attacks on such facilities due to the risk of large-scale civilian harm, the absence of effective enforcement and accountability mechanisms reveals substantial deficiencies in the existing international legal architecture. From a technical perspective, the paper analyses the loss of off-site power (LOOP) as a systemic threat to NPP safety during war. The frequency and duration of LOOP events significantly exceeded design-basis assumptions as a direct consequence of deliberate attacks on high-voltage substations and transmission lines. Power restoration was further complicated by elevated risks to repair personnel, widespread physical damage to infrastructure, cumulative equipment degradation caused by repeated actuations, prolonged operation under degraded grid conditions and increased psychological stress on operating staff. Preventive load reductions and grid instability, including voltage and frequency fluctuations, additionally affected turbine-generator and rotating equipment performance. The paper demonstrates that conventional safety assessment approaches are insufficient when nuclear facilities operate under conditions of large-scale military aggression and argues for the development of advanced analytical frameworks capable of capturing complex interactions between NPPs and degraded power systems. In this context, the methodology developed by EPRI, integrating deterministic grid disturbance analysis with probabilistic safety assessment, is identified as a promising tool for supporting operational decision-making. The Ukrainian experience provides a critical foundation for strengthening both international legal protections and technical approaches to nuclear power plant resilience under extreme external hazards.