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PPOOLEX EXPERIMENTS ON THE DYNAMICS OF FREE WATER SURFACE IN THE BLOWDOWN PIPE
Jani Laine, Markku Puustinen, Antti Räsänen,
This report summarizes the results of the thermal stratification and mixing experiments carried out with the scaled down PPOOLEX test facility designed and constructed at Lappeenranta University of Technology. Steam was blown into the dry well compartment and from there through the vertical DN200 blowdown pipe to the condensation pool filled with sub-cooled water. The main objective of the experiments was to obtain verification data for the development of the Effective Momentum Source (EMS) and Effective Heat Source (EHS) models to be implemented in GOTHIC code by KTH. A detailed test matrix and procedure put together on the basis of pre-test calculations was provided by KTH before the experiments. Altogether six experiments were carried out. The experiments consisted of a small steam flow rate stratification period and of a higher flow rate mixing period. The dry well structures were heated up to approximately 130 °C before the stratification period was initiated. The initial water bulk temperature in the condensation pool was 13-16 °C. During the low steam flow rate (85–105 g/s) period steam condensed mainly inside the blowdown pipe. As a result temperatures remained constant below the blowdown pipe outlet while they increased towards the pool surface layers indicating strong thermal stratification of the wet well pool water. In the end of the stratification period the temperature difference between the pool bottom and surface was 15–30 ºC depending on the test parameters and the duration of the low flow rate period. In the beginning of the mixing phase the steam flow rate was increased rapidly to 300–425 g/s to mix the pool water totally. Depending on the used steam flow rate and initial pool water temperature it took 150–500 s to achieve total mixing. If the test was continued long enough the water pool began to stratify again after the water bulk temperature had reached ~50 °C despite of steam mass flux belonging to the chugging region of the condensation mode map. During the mixing period the steam/water-interface oscillated inside the blowdown pipe with amplitude of 29–999 mm and with an average frequency of ~1 Hz.
condensation pool, steam/air blowdown, thermal stratification and mixing