GOTHIC is an integrated, general purpose thermal hydraulic software package for design, licensing, safety and operating analysis of Nuclear Power Plant containments, confinement buildings and system components. It bridges the gap between the lumped parameter codes frequently used for containment analysis (such as MELCOR, MAAP, COCOSYS, ASTEC codes) and Computational Fluid Dynamics codes. Within a single model, GOTHIC can include regions treated in conventional lumped parameter mode and regions with three-dimensional flows in complex geometries. The heat transfer correlations built into GOTHIC cover the portion of the boiling curve which spans single phase heat transfer up to pre-Critical Heat Flux (CHF) heat transfer. The implemented boiling curve is truncated to exclude post-CHF heat transfer as it has not been adequately verified and was considered by the developers to have little application in general containment analysis. As such, one area that the code is not currently qualified for is post-CHF heat transfer, which could occur for example in the case of In-Vessel Corium Retention, where cooling water enters in contact with the high temperature of the Reactor Pressure Vessel wall. The presented research focuses on creating an external subroutine that solves this limitation, enabling the GOTHIC code to account for CHF phenomena. The modeling of CHF would be very useful in order to enable the code to simulate the external Reactor Pressure Vessel (RPV) Cooling , as well as other types of severe accidents or analyses where post-CHF simulation is required. Several subroutine function switches were implemented in order to facilitate its usage for different types of heat structures and correlations. The subroutine determines the CHF values based on either: the 2006 Groeneveld Look-up Tables, Lookup Tables for Large Diameter Vertical Tubes, Look-up Tables for Large Diameter Horizontal Tubes, or the correlation used by the MELCOR code for critical heat flux situations. It shall be noted that the developed subroutine and its implementation were performed without the need to have access to the GOTHIC source code. In a previous paper, the GOTHIC code was used to perform a containment safety analysis for the Atucha-I NPP (CNA-I) for an in-vessel retention type of analysis. Highly conservative vapour generating boundary conditions were used in order to simulate the boiling between the cavity water and the RPV surface, and to bypass the GOTHIC limitation. The newly developed subroutine was used for the analysis of two postulated Atucha-I in-vessel retention scenarios, a Large Break Loss Of Coolant Accident (LBLOCA) and a Station Black-Out (SBO), with the simulation of heat transfer between RPV and cavity water. Specifically for in-vessel retention situations, a separate user selectable option for the subroutine was developed, in which the Critical Heat Flux is determined based on experiments performed at the ULPU facility from the University of California, Santa Barbara, USA, which were combined with the 2006 Groeneveld Look-up Tables primarily in order to have a pressure dependence. This was performed because for the Atucha-I analysis, the pressure was higher than in the ULPU facility.

GOTHIC 是一个集成的通用热力液压软件包，用于核电站安全壳、隔离建筑和系统组件的设计、许可、安全和运行分析。它弥补了经常用于安全壳分析的集总参数代码（例如 MELCOR、MAAP、COCOSYS、ASTEC 代码）与计算流体动力学代码之间的差距。在单个模型中，GOTHIC 可以包括以传统集总参数模式处理的区域和具有复杂几何形状的三维流动的区域。GOTHIC 中内置的传热相关性涵盖了沸腾曲线的一部分，该部分跨越单相传热到临界热通量 (CHF) 前传热。所实施的沸腾曲线被截断以排除后 CHF 传热，因为它尚未得到充分验证，并且被开发人员认为在一般安全壳分析中几乎没有应用。因此，该规范目前不适用的一个领域是后 CHF 传热，这可能发生在容器内 Corium Retention 的情况下，其中冷却水进入与反应堆压力容器的高温接触墙。所提出的研究侧重于创建一个解决此限制的外部子程序，使 GOTHIC 代码能够解释 CHF 现象。CHF 的建模对于使代码能够模拟外部反应堆压力容器 (RPV) 冷却以及其他类型的严重事故或需要进行 CHF 后模拟的分析非常有用。实现了几个子程序功能开关，以方便其用于不同类型的热结构和相关性。该子程序根据以下任一确定 CHF 值：2006 Groeneveld 查找表、大直径垂直管查找表、大直径水平管查找表或 MELCOR 代码在临界热通量情况下使用的相关性。应该注意的是，开发的子程序及其实现是在不需要访问 GOTHIC 源代码的情况下执行的。在之前的一篇论文中，GOTHIC 代码用于对 Atucha-I 核电厂 (CNA-I) 进行容器内滞留类型分析的安全壳安全分析。使用高度保守的蒸汽生成边界条件来模拟腔水和 RPV 表面之间的沸腾，并绕过 GOTHIC 限制。新开发的子程序用于分析两种假设的 Atucha-I 容器内滞留场景，即冷却液大断裂事故 (LBLOCA) 和站停电 (SBO)，并模拟 RPV 和腔水。专门针对容器内滞留情况，为子程序开发了一个单独的用户可选选项，其中临界热通量是根据在美国加州大学圣巴巴拉分校 ULPU 设施进行的实验确定的，这些实验与2006 Groeneveld Look-up Tables 主要是为了有压力依赖性。