The high-speed ballistic injection of a solid spherical pellet of deuterium into a thermonuclear reactor plasma is studied to determine the feasibility of this technique for controlled thermonuclear reactor fuelling. An evaporation wave front is driven into the solid by the ambient particle energy flux which evaporates the surface of the solid. This evaporated pellet material is an ionized plasma the temperature of which is initially of the order of 104 °K. About one half of the input power to the pellet is convected away by the expanding warm plasma cloud. This evaporated plasma cloud then helps shield the pellet surface from the incident reactor electrons. The dynamics of this pellet evaporation, the expanding plasma cloud, and its shielding effect are studied in detail.The trajectory of the pellet and the deposition of the evaporated material are analysed for the case of high-speed injection into a fusion plasma having a density profile which is characteristic of a large reactor. Sufficient pellet penetration can be achieved by this means at relatively small power expenditure, but very-high-voltage particle acceleration is required to achieve the needed input velocity.