Abstract
In the operating nuclear power plant, piping and components installed in the in-service testing (IST) systems connected to the reactor coolant system are potentially exposed to fatigue caused by thermal stratification flow, possibly threatening its integrity. The emergency core cooling system (ECCS) is one of candidates for which the thermal stratification phenomenon can occur. During the ECCS operating period, buoyancy due to density difference may have significant influence on thermal-hydraulic characteristics of the mixing flow. Therefore, in this study, the need to consider proper buoyancy models in governing equations, especially turbulent transport equations, for accurate prediction of single phase thermal stratification by ECCS injection was numerically studied using ANSYS CFX R17.2.
Highlights
Nuclear power plant operators conduct in-service testing (IST) to verify the safety functions of safety-related pumps and valves, and to monitor the degree of vulnerability over time during reactor operation [1]
The objective of Test 1 is to clarify the phenomenon of temperature stratification on the cold legs and the upper region of downcomer of the reactor vessel, which are important for the evaluation of the pressurized thermal shock (PTS) during the coolant injection by the emergency core cooling system (ECCS), and to obtain the measured data for the main parameters with the aim of validating the simulation code and the numerical modeling
In author’s previous study [6], it was confirmed that the fluid/wall temperature distributions were differently predicted in the cold leg and downcomer;; depending on the Reynolds averaged Navier-Stokes (RANS) based turbulence models
Summary
Nuclear power plant operators conduct in-service testing (IST) to verify the safety functions of safety-related pumps and valves, and to monitor the degree of vulnerability over time during reactor operation [1]. Piping and components installed in the IST-related systems connected to the reactor coolant system are potentially exposed to fatigue caused by thermal stratification flow, possibly threatening its integrity. Numerical analysis using different computer fluid dynamics (CFD) software has been performed to assess the effect of the emergency core coolant injection on single-phase flow mixing in the cold leg [2-4]. There was a significant difference between the predicted and the measured fluid temperature data at several measurement locations. Effect of buoyancy turbulence option, available in ANSYS CFX R17.2, on the prediction accuracy for single phase thermal stratification in the cold leg and downcomer was examined
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