The Dynamic-Implicit-Additional-Source (DIAS) method for multi-scale coupling of thermal-hydraulic codes to enhance the prediction of mass and heat transfer in the nuclear reactor pressure VESSEL

Abstract

The paper describes a Dynamic-Implicit-Additional-Source (DIAS) method for a domain-overlapped multi-scale coupling of a system-code, sub-channel code, and CFD code aiming to improve the simulation of the thermal-hydraulics phenomena e.g. the heat, mass, solute transfer in the Nuclear Reactor Pressure Vessel (RPV). This method is developed to correlate the essential physical parameters predicted by the nuclear system thermal-hydraulic code with more precise data derived from sub-channel or Computational Fluid Dynamic (CFD) solutions, enabling the system-code to produce more realistic mass and heat transfer within the RPV. The DIAS-method is used in combination with the domain-overlapping coupling approach and it currently correlates four system-codes parameters: the coolant velocity, the pressure drop, the coolant temperature, and the boron concentration.The three-dimensional velocity and pressure fields predicted by a sub-channel or CFD codes are used to calculate the new friction and form loss coefficients on the fly (in the momentum equation) at all the overlapped edges in the system-code with increased accuracy. Additionally, the coolant temperature distribution predicted by the system-code is correlated based on the three-dimensional temperature field gained from the sub-channel or CFD codes by adding a dynamic-implicit heat source or sink to the energy equation. Such kind of source/sink was also added to the solubility equation of the system-code to predict the boron concentration based on the corresponding high-resolution fields provided by the high-resolution thermal-hydraulic solvers. All of the three newly added items are named as the Dynamic-Implicit-Additional-Source (DIAS) since they are not the traditional fixed-explicit appendixes to the original system of governing equation set but they are dynamically tuned and implicitly calculated along with the solution process.The complete DIAS-method was verified with an academic 3D coolant-mixing problem in a Reactor Pressure Vessel (RPV). Results obtained from the test cases indicate that the mass, heat and solute transfer in the RPV could be better predicted by the coupled codes with the DIAS method. Finally, the DIAS method is proved an efficient and powerful approach for multi-scale thermal-hydraulic coupling based on the domain-overlapping approach.