VHTR-based power plants' performance enhancement using Rankine cycles

Abstract When very high temperature reactors operate as power plants where helium is being considered as cooling fluid for the primary loop, cost effective performance enhancement can be achieved under safety operating conditions by means of alternative thermal cycles to the conventional steam Rankine and combined cycles. The proposed improvements require the implementation of some Rankine cycle structures operating with carbon dioxide condensed at quasi-critical conditions combined with Rankine cycles coupled in series where carbon dioxide or water are used in order to achieve cooling capacity. Under this structure several cycles are proposed and studied so that according to the chosen performance criteria, a cycle structure is available. The results of the study show that plant structures composed by a high temperature topping Rankine cycle operating with carbon dioxide followed by a low temperature bottoming Rankine coupled in series allow the choice of a plant structure capable of advantageously rendering at least one of the following characteristics without violating safety standards: High net efficiency (from actual 48% to more than 56%) by sacrificing cooling capacity and specific power or high cooling capacity and specific power by sacrificing efficiency.