Abstract One of the key safety components for nuclear fusion plants is the suppression tank, which is designed to protect the Vacuum Vessel (VV) against accidental pressurization events, e.g. Loss Of Coolant Accident (LOCA). In this framework the attention is focused on the Vacuum Vessel Pressure Suppression System (VVPSS), made of water tanks in which the pure steam, or eventually mixed with incondensable gases, is injected and consequently the overpressure is dumped profiting of Direct Contact Condensation (DCC). The design constraints of fusion reactor dictate that the pressure resulting (long-term) from any accidental or baking condition should be always kept lower than 0.15 MPa. The study of the phenomena evolving during DCC in LOCA conditions is the major novelty, especially in consideration of the lack of similar studies in the available literature. In this context, a wide series of experimental tests was carried out at Pisa University (UNIPI), Department of Civil and Industrial Engineering (DICI), in a Small Scale Test Facility (SSTF), designed and instrumented for investigating DCC at sub-atmospheric pressure, by varying water pool temperature, pressure and steam mass flow rate. The adoption and assessment of suitable numerical codes, to reliably simulate such a cutting-edge multiphase multicomponent scenario, have a crucial role for contributing to the phenomena understanding and for possible safety analysis of full-scale components. On this basis, a preliminary evaluation of the cartesian three-dimensional SIMMER IV code capabilities in simulating DCC at sub-atmospheric conditions was carried out, taking as reference one UNIPI test. SIMMER IV code was able to set up precise initial low-pressure boundary conditions and simulate superheated steam condensation in subcooled water pool, with condensation efficiency comparable to the experimental one. Moreover, SIMMER IV code predicted a longitudinal steam plume dimension and injected steam velocity consistent with experimental data.

中文翻译：

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SIMMER IV代码抑制罐亚大气压蒸汽凝结的数值分析

摘要 核聚变装置的关键安全部件之一是抑制罐，它旨在保护真空容器 (VV) 免受意外增压事件的影响，例如冷却剂损失事故 (LOCA)。在此框架中，注意力集中在真空容器压力抑制系统 (VVPSS) 上，该系统由水箱制成，其中注入纯蒸汽或最终与不可冷凝气体混合，从而消除超压，从而受益于直接接触冷凝 (DCC) ）。聚变反应堆的设计约束要求任何意外或烘烤条件产生的（长期）压力应始终保持低于 0.15 MPa。研究在 LOCA 条件下 DCC 期间演变的现象是主要的新颖性，特别是考虑到现有文献中缺乏类似的研究。在此背景下，在比萨大学 (UNIPI) 土木和工业工程系 (DICI) 的一个小型测试设施 (SSTF) 中进行了一系列广泛的实验测试，该设施设计和仪器用于研究亚大气压下的 DCC压力，通过改变水池温度、压力和蒸汽质量流量。采用和评估合适的数值代码，以可靠地模拟这种尖端的多相多组件场景，对于促进现象理解和全尺寸组件可能的安全分析具有至关重要的作用。在此基础上，对笛卡尔三维SIMMER IV码在亚大气压条件下模拟DCC的能力进行了初步评估，以一项 UNIPI 测试为参考。SIMMER IV 代码能够设置精确的初始低压边界条件并模拟过冷水池中的过热蒸汽冷凝，冷凝效率可与实验相媲美。此外，SIMMER IV 代码预测了与实验数据一致的纵向蒸汽羽流尺寸和注入蒸汽速度。