Thermonuclear Fusion

                In my last blog post, I wrote about how an accelerator driven subcritical reactor would be superior to current fission reactors. In this blog post, I will be writing about an alternative to these two choices. This alternative is fusion. Simply put, fission is splitting large atoms, while fusion is combining small atoms. The type of fusion I will be talking about is thermonuclear fusion.

                The first point of comparison will be regarding safety. Nuclear fusion reactors are safer than current fission reactors. Thermonuclear fusion requires a large amount of heat to sustain itself. If the containment is breached such as in the event of a nuclear meltdown, the temperature would drop and it would stop producing heat. The fallout of such an event would be minimal, as it would not have the same energy as a nuclear explosion or the radioactivity, as it would become no longer radioactive when it cools.

                Another problem with conventional nuclear reactors that is overcome in fusion reactors is the production of nuclear waste. The waste from a fusion reaction is almost always stable helium. There are some radioactive isotopes created, but those have extremely short half-lives ranging from less than a second to 12.3 years depending on what fuel is used.

                As with conventional fission reactors, fuel would be a problem for fusion reactors. The fuel for fusion reactors can be different elements and isotopes and mixes of those with varying efficiency, required operating heat, radioactivity, and difficulty to produce. One of the most commonly discussed reactions is between deuterium and tritium. Deuterium is hydrogen with one neutron. It can be extracted from natural water such as the ocean, but current extraction techniques are costly, energy intensive, and inefficient, comparable to enriching uranium. Another way to get deuterium is to make it. This can be done by irradiating hydrogen (normally bonded with oxygen in the form of water) as neutron shielding of fission reactors, or even of other fusion reactors. Tritium is made by irradiating deuterium. Therefore, using water as neutron shielding will produce fuel.

This reactor design, if implemented, would not be dependent on mining of rare elements for fuel, but would be much more difficult and expensive to build. Overall, this type of reactor may not be practical with today’s relative abundance of fission fuels, its cost, and our current technologies for containing the reaction, but the massive amount of power able to be produced in this reaction make it something worth developing.