I heard that the specific radioactivity of power plant waste is high for a short time, but will soon degrade to a radioactive level below that of the ore which the fuel comes from. So a long half life means the specific level of radioactivity is low. I think I would rather live with the additional radioactivity of spent nuclear fuel than the chemical waste products which result in the burning of fossil fuel to generate electricity. You get plenty of chemcial carcinogens from the fossil fuel smokestack, and their half life is infinity.