The nuclear fusion reactor ITER (International Thermonuclear Experimental Reactor) foresees a Pressure Suppression System (PSS) in order to manage a Loss of Coolant Accident (LOCA) in the Vacuum Vessel (VV). A LOCA scenario is postulated to occur in the cooling systems of plasma facing components. The Vacuum Vessel Pressure Suppression System (VVPSS) has a key safety function because a large internal pressure in the VV could lead to a breach of the primary confinement barrier.

Steam condensation would occur in ITER at sub-atmospheric pressure, differently than the applications in nuclear fission reactors. Steam direct contact condensation (DCC) in sub-atmospheric conditions have never been implemented before, therefore an experimental assessment of the VVPSS is necessary to simulate this phenomenon in ITER's thermal-hydraulic conditions.

Under the financial support of ITER Organization, an experimental program was performed at the Department of Civil and Industrial Engineering (DICI) of the University of Pisa in the past 3 years, using a small-scale experimental rig (1/22 scale factor).

In order to assess the scale laws elaborated by means of the experimental results obtained in this small scale facility, a Large Scale facility was built at University of Pisa. This facility is almost a full scale mock-up of ITER's VVPSS from the geometric point of view (1/1.09 scale factor) and it is 1/10 scale factor from the steam mass flow rate point of view.

This paper illustrates the results of the first test campaign. A 1/10 scale sparger system SPS-A (having a diameter equal to DN125 and 100 holes) was used with a maximum steam mass flow rate of 0.5 kg/s. This experimental configuration represents real operating conditions on the basis of the results of elaborated similitude analysis. The preliminary analysis of the experimental results confirms the agreement in terms of condensation regimes between the two reduced scale (1/22 and 1/10 scale) as foreseen by the elaborated scale laws.

核聚变反应堆ITER（国际热核实验反应堆）预见到压力抑制系统（PSS），以便管理真空容器（VV）中的冷却剂泄漏事故（LOCA）。假定在面向等离子体的组件的冷却系统中会发生LOCA情况。真空容器压力抑制系统（VVPSS）具有关键的安全功能，因为VV中的较大内部压力可能会导致违反主要限制屏障。

蒸汽凝结将在低于大气压的ITER中发生，这与核裂变反应堆中的应用不同。以前从未在低于大气压的条件下实施蒸汽直接接触冷凝（DCC），因此有必要对VVPSS进行实验评估，以在ITER的热工条件下模拟这种现象。

在ITER组织的财政支持下，过去3年中，比萨大学的土木和工业工程系（DICI）使用了小型试验台（1/22比例系数）进行了一项实验计划。

为了评估通过该小型工厂获得的实验结果制定的规模定律，比萨大学建立了大型工厂。从几何角度（1 / 1.09比例因子）来看，该设施几乎是ITER VVPSS的完整模型，从蒸汽质量流量的角度来看，它是1/10比例因子。

本文说明了第一个测试活动的结果。使用1/10比例的喷雾器系统SPS-A（直径等于DN125和100个孔），最大蒸汽质量流量为0.5 kg / s。根据详细的相似度分析结果，该实验配置代表了实际的运行条件。对实验结果的初步分析证实了精细比例定律所预言的两个缩小比例（1/22和1/10比例）之间的冷凝方式方面的一致性。