Markku Puustinen, Jani Laine, Antti Räsänen, Eetu Kotro,
This report summarizes the results of the RHR nozzle tests carried out in the PPOOLEX facility at LUT in 2016. The test facility is a closed stainless steel vessel divided into two compartments, drywell and wetwell. For the RHR nozzle tests the PPOOLEX facility was equipped with a model of an RHR nozzle and an associated water injection line.
The main objective of the tests was to obtain additional data for the development of the EMS and EHS models to be implemented in GOTHIC code by KTH. Mixing of a thermally stratified pool with the help of water injection through an RHR nozzle was of special interest. Particularly the effects of nozzle orientation, ∆T in the pool, injection water temperature and injection water mass flow rate were studied.
In the tests there were two stratification phases and two mixing phases. During the stratification phases two regions with clearly different water temperatures and a narrow thermocline region between them developed in the pool. When the target temperature difference between the bottom and the top layer of the pool had been reached the mixing process was initiated by starting water injection into the pool through the RHR nozzle.
With the vertical orientation of the RHR nozzle mixing was otherwise successful but incomplete above the nozzle elevation. This was the case with both of the used water injection flow rates, 0.5 kg/s and 0.3 kg/s.
Compete mixing was achieved with the horizontal orientation of the RHR nozzle by using a large injection flow rate (1.0-1.05 kg/s). The pool mixed in about 4000 seconds. With a 0.3 kg/s injection flow rate the water volume above the thermocline started to cool down as soon as the mixing phase started whereas below the thermocline the mixing process proceeded very slowly and only a small fraction of the bottom volume mixed completely before the test was terminated because the wetwell became full of water.
These tests in PPOOLEX verified that orientation of an RHR nozzle plays an important role in the success of the mixing process of a thermally stratified pool. The nozzle injection flow rate, injection water temperature and ∆T in the pool have an effect on the mixing process but it is not as dominant as the nozzle orientation.