Comprehensive comparison of various working media and corresponding power cycle layouts for the helium-cooled DEMO reactor

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The main goal of this study is to propose a comprehensive view of the benefits of using various working media and thermal cycle layouts for efficient conversion of thermal energy from the helium-cooled DEMO reactor for electricity production. A four-source boundary condition proposed by Bubelis (2018) [1] is used in the power cycle optimization process. Selected power cycle layouts are optimized through a specialized computational optimization code to achieve maximum net power output with variable blanket helium outlet temperature in the range from 380 up to 520 °C. The selected working media are water-steam, supercritical CO2, and helium. The Rankine cycle layout is based on the layout proposed by Rovira (2019) [7] and optimized in the full range of blanket outlet temperature. Investigated S-CO2 cycles are simple Brayton cycle, re-compression cycle, and pre-compression cycle. In the case of the indirect helium cycle, the only reasonable layouts are the simple Brayton cycle and the pre-compression cycle. Study results compare suitability of using the water-steam, S-CO2, and helium cycles for different outlet temperatures of the source as well as a view of their complexity in terms of size and number of components. Presented results show, that the Rankine cycle is the most effective solution from thermodynamics point of view, but S-CO2 cycles can compete with it in size, complexity, cost, and operational flexibility.