Optimization methodology for large scale fin geometry on the steel containment of a public acceptable simple SMR (PASS)

Abstract

Heat removal capability through a steel containment is important in accident situations in order to preserve the integrity of a nuclear power plant which adopts a steel containment concept. A heat transfer rate will be enhanced by using fins on the external surface of the steel containment. The fins, however, create an increase in flow resistance that can deteriorate the heat transfer rate at the same time. This study investigates an optimization methodology of large scale fin geometry for a vertical base where a natural convection flow regime is turbulent. Rectangular plate fins adopted in the steel containment of a Public Acceptable Simple SMR (PASS) is used as a reference. The heat transfer rate through the fins is obtained from CFD tools. A heat transfer coefficient correlation of a vertical fin array considering both natural convection and radiation is suggested. The general functional form of a natural convection heat transfer coefficient is used as the fin effectiveness term considering temperature decrease along the fin height is modified. This is compared with our CFD results. A radiation heat transfer coefficient is obtained analytically by a view factor study. A total heat transfer coefficient is expressed as the sum of the convection heat transfer coefficient and the radiation heat transfer coefficient. Scaling analysis is conducted to show the existence of an optimum spacing which turns out to be 7cm in the case of PASS. In order to optimize fin geometry, an overall effectiveness concept is introduced as a fin performance parameter. The overall effectiveness is expressed as a function of fin geometric parameters, showing that an optimum thickness exists. However, the optimum thickness is changed as a fin height varies. Therefore, optimal fin geometry is obtained as a function of a fin height. With the assumption that the heat removal rate from the finned steel containment is the same as that from the original steel containment, we found out that containment volume and material volume can be reduced as a function of the overall effectiveness; the reduction is 43% of the containment volume and 13% of the material volume as a least-material containment.