In many senses nuclear energy is the cleanest of renewables. It does not produce emissions such as CO2 and greenhouse gases, which are harmful to the population and the environment. Roughly 700 million metric tons of CO2 emissions are avoided each year in the United States by generating electricity from nuclear power rather than some other source; according to the U.S. Department of Energy, that is nearly equivalent to the CO2 released from all U.S. passenger cars.
It is true that it does produce radioactive waste but since this is in solid form it can be dealt with relatively easily and stored away from centres of population. Furthermore, as new technology becomes available to allow the more efficient use of nuclear fuel, less nuclear waste will be produced. (A recent example is the development of the fast breeder reactor, which uses fuel much more efficiently.