The released fuel itself contains uranium-235, uranium-238, and plutonium-239, which are all ultra-long half-life radioactive elements, and their radioactive effects are usually very small. radioactive effects are small, the main one is plutonium, which is a very toxic element, i.e.: the biological effect of plutonium on humans is not radioactive but toxic.
The fission products are more complex, mainly iodine-131, cesium-137, and radon-219 (222?) ....... High concentrations of radioactive iodine and radioactive radon can cause adverse health effects when inhaled. Fortunately, the half-life is relatively short (all only a few days), and after a certain period of time, they will decay to the extent that they have almost no effect; the half-life of cesium-137 is about 30 years, with gamma decay.
The activation products are mainly tritium, with a half-life of about 12.5 years, and the same chemical properties as hydrogen, which can have some effect on human health when inhaled in large quantities (after drinking large quantities of heavy water containing tritium).
Generally speaking, radioactive elements with short half-lives are also highly radioactive, while those with long half-lives are relatively weak.
As for the harmfulness, iodine and radon dominate in the short term, while cesium dominates in the long term.