[en] Under the HHT development program, the high-temperature helium test plant (HHV) was set up on the site of the Jülich Nuclear Research Institute (KFA). This plant, which was erected using public funds supplied by the Federal Republic of Germany, the State of North-Rhine-Westphalia, and the Swiss Confederation, is intended to demonstrate the operational suitability and reliability of the HHV turbo-machine in addition to testing circuit components. It is the largest and one of the most important test plants in the HHT project, since only there it is possible to obtain process data like pressure, temperature, and total helium flow directly comparable with data on a large HHT plant. The decision to build in 1972 was preceded by various design studies made by the industrial and research establishments participating in the HHT project and the Colleges of Advanced Technology in Aachen and Hannover. Here, it was decided not to proceed with the immediately obvious procedure of building a fossil-fuel-fired closed gas turbine circuit with test loop and a power of about 150 MW, because of the special very high material loads occuring in the heater, which would have necessitated the use of little-known materials with the concomitant heavy costs and risks.