The tritium balance in a D-T fusion power reactor to assure a self-sustainable tritium system is discussed in this paper, comparing the amount of tritium consumed in the fueling cycle including the plasma vessel with the amount of tritium generated in the blanket system. It is determined that recovering tritium from the redeposition layer is highly effective in achieving tritium balance. It is also known from this discussion that having a burning plasma with an overall burning efficiency >0.5% is needed to maintain tritium balance. A burning efficiency >3 to 4% is even better because the tritium balance increases. It is also known that a first-wall material having an overall trapping factor >0.005 or that having an overall permeation loss ratio >0.0001 is not desirable because the tritium loss at the plasma vessel becomes too large to maintain the tritium balance. This discussion also finds that a blanket system with an overall breeding ratio of [approximately]1.1 is desirable early in fusion development to maintain a short tritium doubling time.