Abstract

Natural circulation, mixing, and stratification are important phenomena for the design and safety analysis of many advanced reactor designs with passive safety features as well as large open regions, such as pool reactor designs, spent fuel pools, and containments. Various modeling methods ranging from zero-dimensional (0-D) lumped volumes (or perfect mixing) to full three-dimensional (3-D) computational fluid dynamics (CFD) have been used. Historically, 0-D lumped volume approaches, combined with other modeling methods and assumptions, have been applied to perform so-called conservative analyses, but with the advancement of computational resources and best-estimate-plus-uncertainty methods, it is very desirable to have advanced, multidimensional modeling and simulation capabilities to improve the accuracy of reactor safety analyses, reduce modeling uncertainties, and eliminate the modeling distortions that can occur when simultaneously applying conservatisms. In the past decade there have been large investments in the pursuit of new, higher-fidelity modeling and simulation tools. However, GOTHIC^TM, which has been developed and maintained by Zachry Nuclear Engineering (formerly Numerical Applications, Inc.) since the mid-1980s, already provides these capabilities. GOTHIC is an industry-trusted, computationally efficient, coarse-grid multiphase CFD tool that also includes the important attributes of traditional system-level modeling tools, such as component-level models, control system capabilities, and neutron point kinetics models.

GOTHIC applies a domain decomposition approach, allowing various levels of fidelity from 0-D to full 3-D to be applied in a single model, giving the user the ability to focus computational resources in the regions of interest while still capturing the integrated system response and important feedback effects. The result is a general-purpose, multiphysics engineering design and analysis tool that can be used for both light water reactor (LWR) and non-LWR designs. This paper provides an overview of 3-D finite volume modeling in GOTHIC, including the governing equations, turbulence model, and solution methods. Additionally, a few of the verification and validation tests from GOTHIC’s full test suite are presented to demonstrate fundamental capabilities, including laminar flow in a channel of parallel plates, square and rectangular cavity natural convection, natural convection through vertical and horizontal openings, and natural convection associated with a heated horizontal cylinder in a rectangular cavity. Based on the comparisons with the analytical solutions and experimental results, it is demonstrated that the multidimensional model can perform very well for a wide range of applications.

摘要

自然循环、混合和分层是许多具有非能动安全特征以及大型开放区域（例如池式反应堆设计、乏燃料池和安全壳）的先进反应堆设计的设计和安全分析的重要现象。已经使用了从零维 (0-D) 集总体积（或完美混合）到全三维 (3-D) 计算流体动力学 (CFD) 的各种建模方法。从历史上看，0-D 集总体积方法与其他建模方法和假设相结合，已被应用于执行所谓的保守分析，但随着计算资源和最佳估计加不确定性方法的进步，非常需要具有先进的多维建模和仿真能力，以提高反应堆安全分析的准确性，减少建模的不确定性，并消除同时应用保守性时可能发生的建模失真。在过去十年中，在追求新的、更高保真度的建模和仿真工具方面进行了大量投资。然而，哥特式自 1980 年代中期以来，由 Zachry 核工程公司（前身为 Numerical Applications, Inc.）开发和维护的^TM已经提供了这些功能。GOTHIC 是一种业界信赖的、计算效率高的粗网格多相 CFD 工具，它还包括传统系统级建模工具的重要属性，例如组件级模型、控制系统功能和中子点动力学模型。

GOTHIC 应用域分解方法，允许在单个模型中应用从 0-D 到全 3-D 的各种保真度级别，使用户能够将计算资源集中在感兴趣的区域，同时仍能捕获集成的系统响应和重要的反馈效应。结果是一种通用的多物理场工程设计和分析工具，可用于轻水反应堆 (LWR) 和非 LWR 设计。本文概述了 GOTHIC 中的 3-D 有限体积建模，包括控制方程、湍流模型和求解方法。此外，还介绍了来自 GOTHIC 完整测试套件的一些验证和验证测试，以展示基本功能，包括平行板通道中的层流、方形和矩形腔自然对流，通过垂直和水平开口的自然对流，以及与矩形腔中加热的水平圆柱体相关的自然对流。基于与解析解和实验结果的比较，表明多维模型可以在广泛的应用中表现良好。