Conceptual Thermal-Design Options for Pressure-Tube SCWRs With Thermochemical Co-Generation of Hydrogen

Currently there are a number of Generation IV SuperCritical Water-cooled nuclear Reactor (SCWR) concepts under development worldwide. The main objectives for developing and utilizing SCWRs are: 1) To increase gross thermal efficiency of current Nuclear Power Plants (NPPs) from 33–35% to approximately 45–50%, and 2) To decrease the capital and operational costs and, in doing so, decrease electrical-energy costs (∼$1000 US/kW or even less). SCW NPPs will have much higher operating parameters compared to current NPPs (i.e., pressures of about 25 MPa and outlet temperatures up to 625°C). Additionally, SCWRs will have a simplified flow circuit in which steam generators, steam dryers, steam separators, etc. will be eliminated. Furthermore, SCWRs operating at higher temperatures can facilitate an economical co-generation of hydrogen through thermo-chemical cycles (particularly, the copper-chlorine cycle) or direct high-temperature electrolysis. To decrease significantly the development costs of a SCW NPP and to increase its reliability, it should be determined whether SCW NPPs can be designed with a steam-cycle arrangement that closely matches that of mature SuperCritical (SC) fossil power plants (including their SC turbine technology). The state-of-the-art SC steam cycles in fossil power plants are designed with a single-steam reheat and regenerative feedwater heating and reach thermal steam-cycle efficiencies up to 54% (i.e., net plant efficiencies of up to 43% on a Higher Heating Value Basis). It would be beneficial if SCWRs could involve a regenerative feedwater heating and nuclear steam reheat to be able to adapt the current SC turbine technology and to achieve similar high thermal efficiencies as the advanced fossil steam cycles. The nuclear steam reheat is easier to implement inside pressure-tube or pressure-channel reactors compared to pressure-vessel reactors. Atomic Energy of Canada Limited (AECL) and Research and Development Institute of Power Engineering (RDIPE or NIKIET in Russian abbreviations) are currently developing concepts of the pressure-tube SCWRs. Therefore, no-reheat, single-reheat, and double-reheat cycles of future SCW NPPs were analyzed in terms of their thermal efficiencies. On this basis, several conceptual steam-cycle arrangements of pressure-tube SCWRs, their corresponding T-s diagrams and steam-cycle thermal efficiencies are presented in this paper together with major parameters of the copper-chlorine cycle for the co-generation of hydrogen. Also, bulk-fluid temperature and thermophysical properties profiles were calculated for a non-uniform cosine Axial Heat-Flux Distribution (AHFD) along a generic SCWR fuel channel, for reference purposes.