Performance comparison and optimization of two configurations of (Very) high temperature gas-cooled reactors combined cycles

(Very) high temperature gas-cooled reactors have a reactor outlet temperature of 900-1000 °C, which provides a base for higher cycle efficiency by adopting closed nuclear gas-turbine combined cycles (NGTCCs) instead of direct regenerative cycles (RCs). Typical NGTCCs (TCCs) usually only adopt precoolers and do not include recuperators. The analysis of precoolers in the TCC indicates that a simplified TCC (SCC), a TCC without precoolers, has higher cycle efficiency because of a higher reactor inlet temperature. Moreover, a criterion whether a TCC adopts precoolers is derived. If NGTCCs includes recuperators, it becomes a typical compound combined cycle (TCCC). The analysis of recuperators in the TCCC indicates that recuperator's effectiveness should be above 0.7 for high efficiency, otherwise recuperators can only be used to adjust the inlet temperatures of reactors and steam generators. Based on the discussion of precoolers and recuperators in NGTCCs, a simplified TCCC (SCCC) that only including recuperator is proposed. The further parametric calculations show that the optimum cycle efficiency is 50.0-57.8% for RC, 51.5-59.2% for SCC and 53.3-61.5% for SCCC, with a reactor outlet temperature of 900-1200 °C. Once the reactor inlet temperature is limited to 400-750 °C, a threshold value (500-600 °C) of reactor inlet temperature that separates the working condition of SCC and SCCC is obtained. The SCC is most favorable when the limit temperature is below the threshold value; otherwise, the SCCC has the highest efficiency.