Thermal fatigue estimation due to thermal stratification in the RCS branch line using one-way FSI scheme

Abstract

The scheme and procedure for thermal fatigue estimation of a thermally stratified branch line were developed. Oneway FSI (fluid and structure interaction) scheme was applied to evaluate the thermal stratification piping. Thermal flow analysis, stress analysis and fatigue estimation were performed in serial order. Finally, detailed monitoring locations and mitigation scheme for the integrity maintenance of piping were recommended. All wall mesh and transient temperature distribution data obtained from the CFD (computational fluid dynamics) analysis were directly imported into the input data of stress analysis model without any calculation for heat transfer coefficients. Cumulated usage factors for fatigue effect review with nodes were calculated. A modified method that combines ASME Section III, NB-3600 with NB-3200 was used because the previous method cannot consider the thermal stratification stress intensity. As the results of evaluation, the SCS (shutdown cooling system) line, branch piping of the RCS (reactor coolant system) line, shows that the CUF (cumulative usage factor) value exceeds 1.0, ASME Code limit, in case thermal stratification load is included. The HPSI (high pressure safety injection) line, re-branch piping, shows that temperature difference between top and bottom of piping exceeds the criterion temperature, 28℃, and that the CUF value exceeds 1.0. Therefore, these branch pipings require a detailed review, monitoring or analysis. In particular, it is recommended that the HPSI piping should be shifted backward to decrease the influence of turbulent penetration intensity from the RCS piping.

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.…”