During the Second World War, nuclear weapons were developed and used. Obviously they have no part in a utopia, but although these weapons can be taken apart, the materials used to make them will be left behind.
There are high-tech schemes to “zap” away these wastes, but they are enormously expensive and don't actually do the job. In addition, the huge volumes of radioactive wastes left from the manufacture of the weapons will present a threat of cancer for hundreds of thousands of…