CFD Analysis of Thermally Stratified Flow and Conjugate Heat Transfer in a PWR Pressurizer Surgeline

Abstract

Temperature gradients in the thermally stratified fluid flowing through a pipe may cause undesirable excessive thermal stresses at the pipe wall in the axial, circumferential, and radial directions, which can eventually lead to damages such as deformation, support failure, thermal fatigue, cracking, etc., to the piping systems. Several nuclear power plants have so far experienced such unwelcome mechanical damages to the pressurizer surgeline, feedwater nozzle, high pressure safety injection lines, or residual heat removal lines at a pressurized water reactor (PWR). In this regard, determining with accuracy the transient temperature distributions in the wall of a piping system subjected to internally thermal stratification is the essential prerequisite for the assessment of the structural integrity of such a piping system. In this study, to realistically predict the transient temperature distributions in the wall of an actual PWR pressurizer surgeline with a complex geometry of three-dimensionally bent piping, three-dimensional transient computational fluid dynamics (CFD) calculations involving the conjugate heat transfer analysis are performed for the PWR pressurizer surgeline subjected to either out- or in-surge flows using a commercial CFD code. In addition, the wall temperature distributions obtained by taking into account the existence of wall thickness are compared with those by neglecting it to identify some requirements for a realistic and conservative thermal analysis from a safety viewpoint.

Final Report on CFD and Thermal-Mechanical Stress Analysis of PWR Surge Line under Transient Condition Thermal Stratification and an Evolutionary Cyclic Plasticity Based Transformative Fatigue Evaluation Approach without Using S~N Curve: Rev. 1

“…Development of computational fluid dynamics (CFD) model required to model the thermal condition of SL. There are many researchers contributed for CFD modeling of SL or similar component for modeling complex flow mixing and associated thermal stratification [50][51][52][53][54][55][56][57][58][59][60][61][62][63]. In this section we present a detailed parametric study of standalone CFD and coupled CFD and heat transfer (CFD-HT) analysis of SL.…”

“…The flow rate in SL varies according to plant operating procedures and can vary widely from plant to plant. A flow rate of 25-100 gpm is reported in the literature [50][51][52][53][54][55][56][57][58][59][60][61][62][63] We selected a similar flow rate for the parametric studies discussed in this section. To understand the effect of SL flow rate, stand-alone CFD simulations were performed with SL flow rates of 10 gpm, 50 gpm, 100 gpm, and 200 gpm.…”

A Deterministic and Probabilistic Framework for Forecasting of Time-Series Damage States and Associated End-of-lIfe of a Pressurizer Water Reactor Surge Line under Design-Basis and Grid-Load-Following Loading Conditions

“…As design life of NPPs is being extended, it is important to investigate the long-term effects that thermal stratification has on the safety of pressurizer surge lines and other similar components subjected to thermal stratification. Thermal stratification has been studied and reported extensively in the literature [4][5][6][7][8][9][10][11][12][13][14][15]. One common approach to studying this and related phenomena is to use a finite element code.…”

Numerical Simulation of Industrial Flows

“…CFD simulation of heat transfer processes has progressively become an accepted tool for design, optimization, modification and safety analysis of industrial equipment. The applications of CHT reported in the literature range from cases of basic character such as the simulation of impinging cooling jets (Uddin, 2008, Zu et al, 2009 or nozzle flows (Marineau et al, 2006) to more applied cases like heat exchangers (Sridhara et al 2005, Jayakumar et al, 2008, and to more advanced problems in nuclear reactors (Palko & Anglart, 2008, Jo & Kang, 2010, Péniguel et al, 2010 and fusion reactors (Encheva et al, 2007). Most of the examples mentioned above employ a URANS approach, implying that the Reynolds analogy between momentum transport and transport of heat through a turbulent Prandtl number is adopted in the simulations.…”