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 drywell compartment and from there through the vertical DN100 blowdown pipe to the condensation pool filled with sub-cooled water.
The main objective of the experiments was to obtain verification data to be used by KTH in the validation of the Nariai and Aya model for prediction of oscillations in a blowdown pipe. The second objective was to obtain measurement data from those regions of the condensation mode map of Lahey and Moody which were not previously covered in the PPOOLEX tests. 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 (MIX-07…12) were carried out. The experiments consisted of a clearing phase, of a small steam flow rate stratification period and of a higher flow rate mixing period.
During the low steam flow rate (25–40 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 wetwell pool water. In the end of the stratification period the temperature difference between the pool bottom and surface was 18–22 ºC depending on the steam flow rate and the duration of the stratification period.
During the mixing period the steam flow rate was increased rapidly to 75–275 g/s to mix the pool water inventory. The pool water inventory was not mixed completely because of low exit jet velocity in the blowdown pipe. Also the distance between the pipe outlet and the pool bottom was now ~300 mm longer than in the mixing tests carried out in 2012 with the DN200 blowdown pipe, where total mixing was achieved. Thus, the jet did not reach the bottom of the pool to enhance mixing. During the mixing period the steam/water-interface oscillated inside the blowdown pipe with an amplitude of 33–200 mm and with an average frequency of ~2 Hz.
condensation pool, steam blowdown, thermal stratification, mixing