Experimental and theoretical evaluation of the efficiency of a combustion system with recirculation of unreacted hydrogen for heating feedwater at nuclear power plants

The Russian energy development strategy through 2050 calls for the participation of nuclear power plants in regulating daily fluctuations in electrical load. This leads to variable operating conditions at nuclear power plants, which is ineffective due to premature wear of the plant's primary equipment, particularly the fuel cladding in the core, and the nature of chain reactions in the core associated with xenon poisoning. In this regard, this paper examines a system for additional feedwater heating in a NPP steam turbine cycle with recirculation of unreacted hydrogen. This system allows for safe increases in NPP unit capacity during peak electrical load hours while maintaining the plant's baseline operating mode. According to experimental and theoretical estimates, the hydrogen recirculation rate in the hydrogen-oxygen combustion chamber in the 0,2-2 MPa pressure range is 99,5-18,3%. The decrease in recirculation with increasing pressure is due to the active recombination of hydrogen with oxygen during the cooling of dissociated steam, as well as the increasing effect of hydrogen carryover in the condensate due to its increased solubility. With the recombination rate decreasing to 0,97 in the pressure range of 0,2-7 MPa, the hydrogen recirculation rate is 99,5-28,1%. The assessment showed that the absolute internal efficiency of the steam power cycle decreases as the hydrogen consumption for feedwater heating increases. The increase in gross efficiency of the NPP power unit is 0,73-1,78%, and the off-peak electricity conversion efficiency reaches 37,06-25,96%. Maximum efficiency is achieved at a pressure of 1,1 MPa in the hydrogen-oxygen combustion chamber.

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