High resolution calculation of heat transfer in HTGR reactor cavity cooling systems

The Reactor Cavity Cooling System (RCCS) plays a major role in the passive in-depth safety of High Temperature Gas-Cooled Reactors (HTGR). It aims at removing decay heat generated from the core after an emergency shutdown. The heat is removed by means of natural or forced circulation of air, water, or a combination of the two, depending on the design. The heat removal capacity of the RCCS during normal operation and accident scenarios needs to be precisely quantified to assess the safety margin associated with HTGRs. A thermal-fluid and accident analysis Phenomena Identification and Ranking Table (PIRT), which includes scenarios that affect RCCS performance, has recently been published. The PIRT ranks these scenarios by importance and level of knowledge. Most of the scenarios identified in the PIRT would benefit from a detailed Computational Fluid Dynamics (CFD) fluid and heat transfer analysis. This paper discusses the scenarios that would affect proper operation of the RCCS and ways in which detailed CFD modeling would increase the knowledge level for each scenario. The first step to develop the CFD model is to validate the model on existing benchmark cases. This paper presents the available benchmarks and the relevance of the measurements for CFD validation. Modeling techniques for CFD analysis of the RCCS are presented, as are the simulation results for selected benchmark cases.