This report summarizes the results of the preliminary spray tests carried out in the PPOOLEX facility at LUT. The test facility is a closed stainless steel vessel divided into two compartments, drywell and wetwell. For the spray tests the facility was equipped with a model of a spray injection system with four nozzles.
The main objective of the tests was to study interplay between suppression pool behaviour and the spray system operation. Particularly we were interested to find out if mixing of a thermally stratified pool with the help of spray injection from above is possible. An additional goal was to obtain data for improving simulation models related to spray operation in CFD and system codes as well as contribute to the development of the EMS and EHS models for sprays to be implemented in the GOTHIC code by KTH.
In the first two tests the initial stratified situation was created by injecting first warm and then cold water from the tap into the wetwell. In the third test the stratified situation was created with the help of small steam injection through the model of the sparger pipe in PPOOLEX by starting from a cold state. In all three tests, the spray injection flow rate was the maximum available from the water supply system of the laboratory i.e. about 128 l/min. When divided to the four spray nozzles it gives 32 l/min per nozzle.
In the first two tests, mixing of the topmost layers of the pool was achieved easily. The initial temperature difference between the bottom and surface was 28 °C and 33 °, respectively. It can be speculated that the whole water volume could have been mixed if the tests had been continued for a longer period of time.
In the third test, complete mixing of the initial 60 °C temperature difference between the pool bottom and the surface layer was achieved in about 4200 seconds as a result of internal circulation in the pool induced by the density difference between the cold spray water and warm pool water. The pool water level rose by 2 meters during the spray operation.
These preliminary spray tests in PPOOLEX indicate that it might be possible to mix a stratified pool with the help of spray injection from above. If spray injection was continued long enough internal circulation developed and finally mixed the pool.