A time delayed tripartite evolutionary game model of international responses to the Fukushima treated water discharge

On August 24, 2023, Japan commenced the ocean discharge of treated nuclear-contaminated water from the Fukushima Daiichi Nuclear Power Plant, sparking widespread international concern. This study develops a tripartite evolutionary game model incorporating bounded rationality and time-delay effects to analyze strategic interactions among Japan, other countries, and the International Atomic Energy Agency (IAEA). Through the construction of payoff matrices and replicator dynamic equations with delay terms, the model identifies three evolutionarily stable strategies $$\gamma _4(0,0,1)$$, $$\gamma _6(1,0,1)$$, and $$\gamma _8(1,1,1)$$ under specific cost and benefit conditions. Numerical simulations reveal that time delays significantly influence convergence speed and trajectory complexity, particularly for Japan and the IAEA. Parametric analyses show that Japan’s decision to discharge is sensitive to storage costs ($$C_{SJ}$$), discharge costs ($$C_{DJ}$$), export tax revenue loss ($$T_{RJ}$$), and reputational damage ($$I_J$$), while other countries’ responses are shaped by litigation compensation ($$C_{LC}$$) and aid to Japan ($$C_{HJ}$$). The model also aligns with real-world developments such as China’s conditional partial lifting of its seafood import ban in June 2025, exemplifying the stabilizing role of credible international oversight and transparency. This research contributes a novel delayed-replication framework to evolutionary game theory and offers actionable insights for managing transboundary environmental conflicts.