Power generation by nuclear fission is promoted as non-polluting due to the fact that the process releases no carbon. However, this energy source is not non-polluting; it is simply relatively clean during the generating process itself. The mining process uses quite a bit of fossil fuel to produce the raw uranium to fuel the reactors, and there has never been a clean mining procedure.
The generating process with the reactor on line also causes thermal pollution with the secondary loop cooling water absorbing heat energy from the primary reactor cooling loop and being circulated into an outdoor pond or through the parabolic cooling towers that have become an immediately recognizable emblem of the industry. Cooling ponds of many acres area can have temperatures above seventy degrees Fahrenheit in the dead of a northern states' winter.
Worst of all is the question of the disposition of spent fuel and the decommissioning of these plants. More than sixty years into the commercial nuclear age, we still have no clear concept of how to guarantee safe, permanent disposal of these materials to maintain containment of the radioactivity that remains deadly for thousands of years.
Our search for geologically stable places to dispose of these materials has yielded little but the knowledge that Earth has no geologically stable areas on the required time scales. Then there is the problem of how to communicate with people ten thousand years along, when we have no idea of what their language or culture will be, except that it is likely to be very different from ours.
This is also the technology that yields byproducts that may be enriched to weapons grade. Such enriched uranium and plutonium are the critical components of nuclear weapons, and we already have as much of that as we can stand.
This clean technology has yet to advance very far beyond theory, but has long been the holy grail of nuclear engineering. A fusion reaction arises from plasma composed of deuterium and tritium, which are hydrogen isotopes, being fused together; releasing tremendous energy and the leftover "ash" of the reaction is helium.
The problems that are being addressed in this research are containment, and sustaining a reaction for more than millionths of a second at a time.
The nuclear plasma inside a fusion reactor must reach a temperature of two hundred million degrees Fahrenheit to force the isotopes in the suspended plasma close enough to make them fuse, and there is no material known that can stand up to contact with that temperature. As a result, a powerful magnetic field is required to suspend the reaction inside, but not touching, the reactor.
Initiating the reaction itself is accomplished by concentrating a bank of high-powered lasers on a pellet of the fuel to raise it to the required temperatures. The technology to keep the reaction going is, evidently, still inside that grail; and the scientists and engineers do not expect to produce a sustained controlled reaction until somewhere around the middle of this century.