- The Chernobyl reactor used enriched Uranium dioxide as fuel, which also contained Plutonium produced through neutron capture. - The accident released a mix of fission products (like Iodine-131, Cesium-137, Strontium-90) and transuranic elements (like Plutonium and Americium) into the environment. - Radioactive Plutonium isotopes have long half-lives and are alpha emitters, posing a significant internal contamination hazard and long- term risk, particularly near the plant site where heavier particles settled.