Tokyo Electric Power Company announced to discharge the contaminated radioactive water resulting from the Fukushima nuclear accident into the ocean after purification from 2023. Concerns remain about safety and removal efficiency of radionuclides. This study calculated the total radioactivity and simulated the marine transport of 137Cs, 90Sr, and tritium. It assessed activity concentration in ocean and marine products, lifetime doses from marine product consumption, and associated cancer risks. We found the radionuclides would be globally distributed and penetrate into deep ocean, with the highest concentrations along Japan's eastern coast. If 137Cs and 90Sr were not removed, related cancer risks would range between 8.64 - 33.35 cases per 100,000 people, depending on age and discharge scenario. Risks would be below one case per 100,000 if only tritium is present. Efficient removal of radionuclides is crucial to mitigating health risks. This study provides evidence of potential health risks and recommendations for prevention.