The Design Point (DP) performance of a Nuclear Power Plant (NPP) is fairly straightforward to establish for a given mass flow rate, turbomachinery compressor Pressure Ratio (PR) and reactor Core Outlet Temperature (COT). The plant components are optimum for that point but this is no longer the case if the plant’s operating conditions are changed for part-load performance. Data from tests or previous operating experiences are useful in determining typical part load performance of components based on characteristic maps. However, when individual components are linked in a plant, the range of operating points for part load performances are severely reduced. The main objective of this study is to derive Off-Design Points (ODPs) for the Simple Cycle Recuperated (SCR) and Intercooled Cycle Recuperated (ICR) when considering a temperature range of −35 to 50°C and COTs between 750 to 1000°C, using a modelling & performance simulation tool designed specifically for this study, which calculates the best operational equilibrium ODPs that are critical to the economics of the NPP. Results show that the recuperator High-Pressure (HP) side and reactor pressure losses alter the actual operating parameters (mass flow rate and compressor PR). The SCR yielded a drop in plant cycle efficiency of 1% for a 4% pressure loss in comparison to the ICR (5%) for the same amount of recuperator HP losses. Other parameters such as the precooler and recuperator Low-Pressure (LP) losses still retain the same operating inlet PRs and mass flow rates regardless of the magnitude of the losses. In the absence of characteristic maps in the public domain, the ODPs have been used to produce characteristic trend maps for first order ODP calculations. The analyses intend to aid the development of cycles for Generation IV NPPs specifically Gas Cooled Fast Reactors (GFRs) and Very High Temperature Reactors (VHTRs), where helium is the coolant.

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