There are a lot of fears commonly held by people who oppose nuclear energy. Some feel that a nuclear power plant can explode like a nuclear bomb or that nuclear energy is bad for the environment or perhaps even not safe. Technically, a nuclear power plant could have a melt down under the worst case scenarios but certainly not explode like an atom bomb. The explosion from Chernobyl was actually a chemical explosion. Most chemical explosions involve an extremely rapid oxidation reaction (otherwise known as burning) although this was not the initial type of explosion which occurred at Chernobyl. Chernobyl had the highest heat increase any nuclear power plant could create which was so high that the water coolant turned into steam almost instantaneously. When any substance is converted from a liquid or solid into a gas, its volume increases by approximately 1000 times. This extremely rapid water expansion was the actual initial Chernobyl explosion, the reactor core being made of graphite then later ignited and burned soon afterwards causing the resultant massive radioactivity release which followed. The explosions at Fukushima did not occur in the reactor compartment but rather at a separate location where flammable gases gathered. The flammable gas was created from the same root cause as the meltdown in that reactor but again, no nuclear yield explosion, only chemical.
Technically any human activity is bad for the environment if environmental damage is defined as any alteration of the environment. Even if you only go so far as to say reducing a native animals habitat or destroying plants is not environmentally friendly, you run into some difficult choices. You can’t even build yourself a home without reducing habitats. Wind turbines, solar panels and hydroelectric dams all reduce plant and animal habitat, how much habitat reduction is acceptable for a technology or activity to be environmentally friendly? Nuclear power offers the highest power output per acre out of all commercially available power sources meaning that you get the smallest habitat reduction for the same electricity production with nuclear.
How much pollution can any source of electricity create before that pollution results in being environmentally harmful? Many technologies are available which after being manufactured, built and installed, no longer emit greenhouse gasses during their operation. This includes, geothermal, nuclear, solar, wind and water. Is that all it takes for them to be environmentally friendly? Biofuels are effectively greenhouse gas neutral in that the remove as much as they create making this environmentally friendly in that sense. These like all technology also produce additional waste at the end of their lifetime when the installations have to be replaced.
Nuclear is similar to fossil fuels in the sense that nuclear power does indeed generate waste during its operation with the biggest difference being the volume of waste generated. One might be tempted to think that the biggest difference in waste products is that nuclear power generates radioactive waste but the real scientific truth is that the waste from most fossil fuel is also radioactive. The radioactivity in fossil fuel (mainly coal) is simply diluted by the enormous volume of that waste such that the amount of radioactivity per mass in fossil fuel ash is fairly low (but much higher than common environmental levels). Even the waste from most biofuels is radioactive. Virtually all biofuel molecules contain one or more carbon atoms. On earth, all organic carbon from natural plant growth contains some fraction of the radioactive isotope carbon-14. This isotope of carbon is a naturally occurring radionuclide in all trees and plants covering the planet. This radioactive carbon gets converted to radioactive carbon dioxide in the waste products of the burning biomass or similarly derived biofuels. The concentration in all these instances of the radioactivity is very low, it is just averaged over large volumes and masses. If the radioactivity alone were sufficiently extracted, it could be concentrated to dangerous levels as it is not at dangerous levels in the biofuels waste products as they are generated. With used nuclear fuel, the concentration of radioactivity is already at dangerous levels, there is just a very small volume of it as it is not spread out over large volumes or masses. One subtle but clear difference in these waste products is that spent nuclear fuel does not currently have a permanent disposal option whereas all the radioactivity in coal ash is easily disposed of or even recycled by becoming an additive to concrete. Another difference is that the radioactivity in fossil fuels is naturally occurring whereas the radioactivity in nuclear waste from nuclear reactors is primarily man made.
Although typical safety rates at nuclear power plants are some of the most impressive of all industrial work settings, this does not mean that obtaining and maintaining a good safety record is easy. Safety is in the design and operation of any system or technology.