This study examines how radionuclides released from nuclear power plants are transported and transformed in the global ocean over time. Using an advanced ocean simulation model, it focuses on radionuclides released during the Fukushima accident and from planned wastewater discharges. The findings show that some radionuclides can travel across the Pacific within a few years and gradually spread to other ocean basins by mid-century, emphasizing potential long-term environmental impacts.