This paper describes construction and experimental research activities with two test facilities, PACTEL and PWR PACTEL. The PACTEL facility, comprising of reactor pressure vessel parts, three loops with horizontal steam generators, a pressurizer, and emergency core cooling systems, was designed to model the thermal-hydraulic behaviour of VVER-440-type reactors. The facility has been utilized in miscellaneous applications and experiments, for example, in the OECD International Standard Problem ISP-33. PACTEL has been upgraded and modified on a case-by-case basis. The latest facility configuration, the PWR PACTEL facility, was constructed for research activities associated with the EPR-type reactor. A significant design basis is to utilize certain parts of PACTEL, and at the same time, to focus on a proper construction of two new loops and vertical steam generators with an extensive instrumentation. The PWR PACTEL benchmark exercise was launched in 2010 with a small break loss-of-coolant accident test as the chosen transient. Both facilities, PACTEL and PWR PACTEL, are maintained fully operational side by side. 1. Introduction Since 1976, thermal-hydraulics of nuclear power plants has been studied experimentally at Lappeenranta University of Technology (LUT). During the years, several experiment facilities have been built to study the behaviour of light water reactors. Experimental work with the separate effect test facilities and the large integral test facility has generated a wide data base containing about 900 experiments. Along the years the cooperation with Technical Research Centre of Finland (VTT) induced the decisions to build many of the test facilities utilized at LUT, including the largest one, that is, the parallel channel test facility (PACTEL), described in [1–4]. In Finland, in addition to international cooperation, own research and continuous development of know-how has always been part of the national nuclear safety concept, especially when connected with the specific nuclear power plant types operated in Finland. Hence, the PACTEL facility was constructed in 1990 to have a large-scale test facility available for studies of thermal-hydraulics of a VVER-440 type nuclear power plant. The two units of the Loviisa power plant in Finland are of this type. PACTEL has been utilized in several versatile experimental applications along the years as presented, for example, in [1]. As a new EPR-type pressurized water reactor (PWR) is under construction in Olkiluoto in Finland, national research activities on PWR behaviour are being intensified. The
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