💧 Chapter 4: Improvement of Steam Power Cycles

Boosting the Performance of Steam Cycles

How to enhance efficiency in nuclear steam cycles?

  • Key Strategies:
    • Reheat: Improves steam quality at expansion end (+several % efficiency).
    • Regeneration: Feedwater heaters reduce economizer irreversibilities (e.g., AGR with 8 extractions).
    • Supercritical cycles (221.2 bar): Up to 47-48% efficiency (e.g., Canadian SCWR).
  • Advanced Technologies:
    • Sodium-cooled fast reactors (SFR).
    • Chinese HTR-PM (helium, 750°C).
  • Case Study:
    • Hartlepool AGR: Progressive modeling with Thermoptim (cascaded drains, CO₂ heat exchangers).

Result: Concrete efficiency gains, validated by exergy balances.

Abstract

This chapter presents methodologies for improving steam power cycle performance in nuclear power plants, focusing on high-temperature variants of the Hirn (Rankine with superheat) cycle. Beginning with an analysis of the basic cycle’s limitations through exergy balances, the chapter demonstrates that nearly half of all irreversibilities occur in the economizer due to large temperature differences with the hot source. Two primary improvement strategies are systematically examined: reheat cycles, which increase quality at expansion end and improve efficiency by several percentage points, and regenerative cycles using feedwater heaters with steam extraction, which significantly reduce economizer irreversibilities. The Hartlepool AGR nuclear power plant serves as the primary case study, with progressive modeling refinements incorporating multiple extractions, cascaded drain configurations and CO₂ heat exchangers. The chapter also examines supercritical water cycles operating above 221.2 bar, achieving efficiencies up to 47-48%, and discusses advanced reactor technologies including sodium-cooled fast reactors (SFR), the Chinese HTR-PM high-temperature reactor, and Canadian SCWR designs. Detailed technological aspects of feedwater trains, closed feedwater heaters with cascaded drains, and material constraints in AGRs are presented alongside Thermoptim simulation models and exergy analyses demonstrating the quantitative impact of the various improvements.