Thermal-Hydraulic Analysis of a Once-Through Steam Generator Considering Performance Degradation

A small modular reactor (SMR) has received much attention due to its high flexibility and modularity in design, less on-site construction, short construction time, and high cost-effectiveness [1]. Several countries have entered into a global race for the commercialization of SMRs, and considerable research and development have been implemented. Among the various reactor designs, many SMRs have adopted an integral type pressurized water reactor (PWR) to enhance the nuclear safety and system reliability [2,3]. In the integral reactor design, a single reactor pressure vessel contains primary system components such as fuel and core, steam generators, pumps, and a pressurizer. For the component integration into a reactor vessel, it is important to design each component as small as possible. Thus, it is a common practice to employ a once-through steam generator in the integral reactor design due to its advantages in compactness [4]. Fig. 1 shows the exterior view of a once-through steam generator using helically coiled tubes considered in the present study. In general, gradual degradation in thermal-hydraulic performance of the steam generator occurs with time, and it changes slowly the operating point of the steam generator during plant lifetime. For long-term operation, therefore, it is necessary to predict the operating points according to the degradation rate. For this performance prediction, the thermal-hydraulic performance of the helically coiled tube once-through steam generator is numerically evaluated in this paper. The intention of this paper is to investigate the operation strategies of the steam generator with degradation in performance.