The advantages of gas turbine power plants in general and closed cycle systems under gas pressure in particular for waste heat recovery are well known. A satisfactory efficiency for electric power generation and good conditions to obtain a significant amount of hot water above 100°C lead to a high fuel utilization. However, as in most of projects, it is not much possible to produce high temperature steam or water without significantly decreasing the electricity production. A new method for an additional generation of high quality process or domestic heat is proposed. The basic feature of this method lies in arranging one or two steam generators or preheaters in parallel with the low pressure side of the recuperator. The high total efficiency and the noteworthy flexibility of this system are emphasized. This arrangement is suitable for any kind of heat source, but the applications presented in this paper are related to helium direct cycle nuclear power plants the main features of which are a single 600 MW(e) turbomachine, a turbine inlet temperature of 775°C, no or one intermediate cooling and a primary circuit fully integrated in a pre-stressed concrete reactor vessel.

The concept of a helium cycle nuclear power plant with a single turbomachine located outside the P.C.R.V. in a leaktight basement is being studied. Main features of the system are pointed out, as are the favorable aspects it offers for a satisfactory design of the plant, a high safety level, a good efficiency for electricity generation associated with a dry cooling tower and heat recovery in good conditions for heating or industrial purposes. Above all, the high technological credibility due to the temperature of 750 C is worth being emphasized. In this paper, a 750 C/800 MWe power plant (2000 MWt) with one intercooler is presented as an example of a possible first generation of gas turbine HTGR. Development prospects for higher power levels, 1000/2000 MWe, are also investigated, at first with one but also with two intermediate coolers, taking into consideration the somewhat higher-helium temperature. The net plant efficiencies, for electricity generation only, range from 40 to 45 percent.