Next step fusion energy devices will burn fuel composed for deuterium (heavy hydrogen) and tritium (radioactive hydrogen).
Tritium is of particular concern since it only occurs naturally in minute amounts, and it is hazardous due to its radioactivity. Thus, practical fusion machines must: (1) breed all of their tritium (from neutron-lithium reactions); (2) purify and recycle tritium with high efficiency (less than 5% burns per pass through the reactor; and, (3) safely contain and handle tritium.
Development and demonstration of such systems has progressed at a number of facilities in the U.S. and around the world. However, the unique requirements of tritium processing has made this development challenging, and next generation fusion experiments (e.g., ITER) will require significant scale-up from present, limited experience.
Present R&D efforts are focused on a variety of topics necessary to achieve the daunting requirements of next generation fusion machines.