Can Deuterium undergo a nuclear fusion without the presence of Tritium? I've been reading about fusion fuels for a while now, and I understand that in Lithium-Deuterium fuel, the neutrons from the fission reaction bombard the Lithium to produce Tritium and the D-T reaction occurs and we get the energy.
So what about Deuterium-Deuterium fusion ? Is it possible without the presence of Tritium at all ?
If so, then does it release more or less energy than D-T fusion ? 
 A: All three isotopes of Hydrogen can undergo fusion under the right conditions. The main reason to use D or T is that they fuse more easily than H. For example, H-H fusion is primarily what drives our sun, but in the lab D-D or D-T reactions are much easier to initiate. 
The D-T reaction gives off 17.6 MeV of energy, D-D actually has 3 different reactions it can undergo (4, 3.3, 23.9 MeV), T-T gives 11.33 Mev, D-H gives off 5.5 MeV and H-H fuses into D giving off 1.44 MeV.
A: Deuterium-Deuterium fusion without Tritium is very possible.
Historically, D-D fusion was the first form of nuclear fusion mankind successfully achieved.
It may be worthwhile remembering that, at the dawn of the nuclear age in 1952, an inertial confinement fusion experiment that used nuclear fission to produce the conditions for nuclear fusion called Ivy Mike not only produced net energy (more energy out of the fusion experiment than the energy required to operate the fusion experiment) but achieved a fusion gain factor of Q>=100,000. 
Ivy Mike achieved net energy and Q>=100,000 using the D-D fusion reaction.
Note: No other non-military pure fusion experiment in the world has achieved a fusion gain factor Q>1 at any time, even for milliseconds, in the last 60 years.
(Picture of Ivy Mike D-D fusion experiment - 1952)http://www.sonicbomb.com/content/atomic/carc/us/ivy/limg/mikedevice.jpg
