Thermohydraulics 1100-TERM

Day 1
Development of a new nuclear reactor design involves reliable analysis tools to investigate the feasibility of its conceptual design or to determine specific parameters needed for the design optimization. And the advanced modeling and simulation are expected to play a major role for the development of a new nuclear reactor. One of the fast and effective ways for the students to understand the design concept of a nuclear reactor and the underlining physics would be by learning relevant analysis tools for the investigation of a conceptual design. The class provides an overview of state-of-the-art research and development status in modeling and simulation technology for nuclear reactors.
Modeling and simulation of a nuclear reactor consist of multi-physics including neutron kinetics, thermal hydraulics, and fuel mechanics, among which thermal hydraulics play a major role for the safety and performance analysis. The students will acquire foundational knowledge of thermal hydraulic models adopted in the safety and performance analysis codes for nuclear reactors.

Day2
Advanced thermal hydraulic simulation of nuclear reactors is introduced using the CUPID code, which is a 3-dimension 2-phase flow analysis code developed by the lecturer when he worked for Korea Atomic Energy Research Institute (KAERI). Mathematical and physical models adopted in CUPID will be presented. Then, the application of CUPID for nuclear thermal hydraulic analysis will be introduced. Wide range of applications will be discussed from the CFD-scale analysis to resolve local phenomena to a safety analysis for the whole reactor coolant system. Multi-scale and multi-physics analysis methods are applied for the high-resolution safety analysis using CUPID. The concept of multi-scale and multi-physics analysis will be explained with their applications.

Day 3

This class provides the fundamental knowledge on how to solve the governing equations employed in the nuclear thermal hydraulics analysis. It begins with an introduction of the governing equations, expressed as partial differential equations, used in the safety and performance analysis codes. The numerical methods include discretization of the partial differential operators and solution schemes of the discretized linear equations. The finite difference method (FDM) and finite volume method (FVM) will be explained for the discretization of the governing equations. Different solution schemes are introduced for single- and two-phase flow applications. For the two-phase flow, phase coupling schemes are discussed to deal with the interfacial mass, momentum and energy transfers. To enhance understanding, numerical experiments are provided for simple one-dimensional (1D) and two-dimensional (2D) conceptual problems.
The course specifically emphasizes acquiring practical knowledge of numerical methods for nuclear thermal hydraulics. To achieve this, students will learn how to apply these numerical methods in real-world scenarios by developing pilot code for given exercise problems. The Fortran language will be used for writing this pilot code. In addition, students will learn how to write, compile, and execute a Fortran program.

Day 4
Current computers, including lap top and desk top PCs, are equipped with multi-core processors. Parallel computing, which utilizes multiple processors (cors) simultaneously, is essential for a practical application of advanced simulations. Parallel computing methods can be classified depending on whether it is based on "shared memory" or "distributed memory". The "shared memory" parallel comupting is relatively easy to implement, however it is not efficient for a large scale computation. On the other hand, "distributed memory" parallel computing is complex and difficult to implement, but it shows a good scalability for a large scale computation. The class provides an introduction to a "distributed memory" parallel computing method using the MPI library. Major MPI functions will be introduced and the students will learn how to generate a MPI parallel program through simple exercises. Calculation domain (grid or mesh) decomposition method, which is necessary for the MPI parallel computation, will be explained using a sample calculation mesh. The MPI parallel method will be implemented in the pilot code developed in the previous lecture. And the students will have a chance to test the parallel performance of the pilot code.

Day 5

This class provides a hand on exercise of the CUPID code. There will be a CUPID user guide before the exercise, which includes description of the major input, calculation mesh input, and output processing. A CUPID executable will be available with limited approval for the class so that the students could run the CUPID code if they bring their lap top computers. A set of test problems will be provided for the exercise with the description of the problem definition and relevant input parameters. The test problem includes single/two-phase flow verifications and validations against experiments related to nuclear thermal hydraulics.