Besides the closed-cycle gas turbines built by Escher Wyss and its licensees, a number of notable and very comprehensive studies were carried out. Following the logical realization that closed-cycle gas turbines are needed where a working medium other than air is used, these studies also concerned working media other than air, such as nitrogen, helium and carbon dioxide. Nitrogen can be used as an inert gas similar to air, as is necessary for example for reasons of safety when re-gasifying liquid natural gas. Helium has the lowest neutron capture cross section and is therefore suitable as a coolant for high temperature nuclear reactors and fast breeders. Furthermore, helium is that working medium for gas turbines that allows the highest power output of the turbo machinery. Additionally, because of its high specific heat capacity and low density, it has excellent heat transport and transfer properties. Carbon dioxide was studied as an alternative to water steam for secondary conversion systems in fast breeder reactors. The most important of these studies, carried out in international cooperation, are listed below:
8.1 Helium and Carbon Dioxide Turbines for a Fast Breeder
8.2 High-Temperature Reactor with a Helium Turbine in a Direct Cycle
8.3 Helium Turbines for the Use of Solar Energy
8.4 Nitrogen Turbines for Re-gasifying Liquid Natural Gas