Electric power from near-term fusion reactors

Near-term fusion reactors such as FED or INTOR will probably have primary cooling systems which operate at temperatures lower than is optimal for power production using a conventional steam cycle. This limitation may be imposed by uncertainties in materials behavior or structural limitations. There are economic motivations to demonstrate electric power production from fusion at the earliest possible date. A greater motivation is the elicitation of public interest in and support of fusion as a viable power source. This paper examines requirements and possibilities of electric power production on near-term fusion reactors using low temperature cycle technology similar to that used in some geothermal power systems. Requirements include the need for a working fluid with suitable thermodynamic properties and which is free of oxygen and hydrogen to facilitate tritium management. Thermal storage will also be required due to the short system thermal time constants on near-term reactors. It is possible to use the FED shield in a binary power cycle, and results are presented of thermodynamic analyses of this system. Thermal storage is accomplished by using the latent heat of fusion of a PbBi eutectic. The secondary loop can use R-11, R-113, or hexafluorobenzene as a working fluid. Such a system would cost about $50 million and would generate about 10 MW of electric power