The existing tritium resource available for future fusion power plant D-T operation is severely limited. It is essential to breed tritium to maintain the continuous consumption in the D-T plasma so as to sustain the required fusion power. A minimum criterion of calculated tritium breeding ratio (TBR) >1.1 is adopted to ensure tritium self-sufficiency, allowing a 10% safety margin to cover calculation uncertainties. In a DEMO reactor, there are various factors impacting the availability and effectiveness of fusion generated neutrons for production of tritium. In this paper, the study focused on the impact of first wall design including materials and first wall thickness, and blanket coverage aspects such as divertor geometry and the provision of equatorial heating and diagnostic ports.