Features of adapting gas turbine cycle and heat exchangers for HTGRs

Problems of adaptation of the closed direct gas turbine cycle to nuclear power plant with HTGRs for producing electricity with high efficiency and safety are considered. It should be noted that only in such combination advantages of HTGR producing high-temperature heat with outlet helium temperature of up to 1000 deg. C could be realized, in comparison with other reactor plants. As for reactor plants with steam turbine cycle, there are no problems with transients and disconnection of Power Conversion Units (PCU) at abnormal situations since there is substantial experience in operation of such plants (nuclear engineering was based on steam-turbine cycle from the very beginning) and experience in steam turbine units design. In similar situations, HTGRs with gas turbine cycle rise more problems concerning PCU control and serviceability and, in particular, risk of turbomachine overspeeding, serviceability of heat exchanges and so on. Also, a difficulty to be resolved is normal start-up of reactor plant together with turbomachine, compressors of which supply the core with gas flow. For competitiveness of reactor plants with gas-turbine cycle in comparison with other NPPs and conventional power plants on fossil fuel, heat exchange equipment of gas turbine cycle should have unique performances to provide for plant efficiency of up to 50%. For this purpose, heat exchangers should have high compactness and minimal pressure losses to allow assembling within vessels with limited dimensions and should operate under significant pressure differences between circuits (up to 5 MPa) and at high temperatures of up to 600 deg. C. Approaches to the solution of the noted problems are reflected in the report with reference to the modular helium reactor with gas turbine (GT-MHR) developed in the international cooperation. (author)