An Optimal Design Approach for the Decay Heat Removal System in PGSFR

Sodium-cooled Fast Reactor (SFR) is one of the generation IV (Gen-IV) nuclear reactors. Prototype Gen-IV SFR (PGSFR) is a SFR being developed in Korea Atomic Energy Research Institute (KAERI). Decay Heat Removal System (DHRS) in the PGSFR has a safety function to make shutdown the reactor under abnormal plant conditions. Single DHRS loop consists of sodium-to-sodium decay heat exchanger (DHX), helical-tube sodium-to-air heat exchanger (AHX) or finned-tube sodium-to-air heat exchanger (FHX), loop piping, and expansion vessel. The DHXs are located in the cold pool and the AHXs and FHXs are installed in the upper region of the reactor building. The DHRS loop is a closed loop and liquid sodium coolant circulates inside the loop by natural circulation head for passive system and by forced circulation head for active system. There are three independent heat transport paths in the DHRS, i.e., the DHX shell-side sodium flow path, the DHRS sodium loop path through the piping, the AHX shell-side air flow path. To design the components of the DHRS and to determine its configuration, key design parameters such as mass flow rates in each path, inlet/outlet temperatures of primary and secondary flow sides of each heat exchanger should be determined reflecting on the coupled heat transfer mechanism over the heat transfer paths. The number of design parameters is larger than that of the governing equations and optimization approach is required for compact design of the DHRS. Therefore, a genetic algorithm has been implemented to decide the optimal design point. The one-dimensional system design code which can predict heat transfer rates and pressure losses through the heat exchangers and piping calculates the objective function and the genetic algorithm code searches a global optimal point. In this paper, we present a design methodology of the DHRS, for which we have developed a system code coupling a one-dimensional system code with a genetic algorithm code. As a design result, the DHRS layouts and the sizing of the heat exchangers have been shown.