Summary of the work at KTH:
Effective Heat Source (EHS) and Effective Momentum Source (EMS) models have been developed to enable predicting the long-term thermal behavior of a large water pool during a steam injection through blowdown pipes and spargers. Validation of the EHS/EMS models was done using experimental data from the PPOOLEX and SEF-POOL facilities at LUT, Finland, and the PANDA facility at PSI, Switzerland. The validated models have been applied to full-scale analysis of a Nordic BWR Pressure Suppression Pool (PSP) during a steam injection through spargers. The results show that strong thermal stratification of potential safety importance can develop in the pool during prototypic steam injection conditions. The analysis results suggest that further development of the EHS/EMS correlations and computational models is necessary in order to enable modeling of regimes and conditions, which have not yet been studied in experiments, but are critically important and can completely change the PSP stratification and mixing behavior. More specifically, non-condensable gases in case of steam injection through blowdown pipes can affect chugging phenomena and thus pool mixing. Steam injection regimes through spargers, the effect of the load reduction rings, azimuthal velocity distribution and turbulence generated at sparger head are also very influential factors according to the analysis. The effects of other safety systems such as sprays and strainers also has not been addressed in experiments. In this project, KTH will provide analytical support for design of the new experiments in the SEF-POOL and PPOOLEX facilities at LUT and in the PANDA facility at PSI (in the framework of the OECD/HYMERES-2 project). Obtained experimental data will be used by KTH for development and validation of the models in order to address the remaining important sources of uncertainty for prediction of the pool behavior.
Summary of the work at LUT:
A set of experiments with spargers were performed in the PPOOLEX facility. The experiments were mainly focused on the oscillatory bubble regime, and exploratory tests were done in chugging and stable jet regimes. The experimental data was used by KTH to address important phenomena governing the pool behavior and validate the computational models. A small-scale Separate Effect Facility (SEF-POOL) was built to measure directly the effective momentum induced by steam injection through a sparger. A total of 19 experiments were performed, which enabled the developed effective momentum correlations to be used in the simulations performed at KTH and an validation effort of CFD models at VTT. Important variables affecting the effective momentum magnitude in full-scale plant need to be further analyzed in order to provide closures for the EMS model development for spargers by KTH. Furthermore, data on direct contact condensation gathered with the help of sophisticated instrumentation is needed for the improvement of calculation models of CFD codes at VTT. For this purpose further development of the experimental facilities for obtaining systematic data relevant to PSP phenomena and conditions will be carried out in this project. Particularly, injection plates with chamfered holes will be manufactured to be used in tests in 2019. Design for new experiments that can adress the effect of momentum distribution in azimuthal direction, turbulence generated by steam condensation and chugging regimes in spargers will be developed in 2019-2021. Feasibility of a new experimental campaign in PPOOLEX facility will be evaluated, considering remaining uncertainties in the phenomena such as effect of spray activation in the drywell and/or wetwell on a thermally stratified pool, combined affect of spargear head and load reduction rings, etc.
Summary of the work at VTT:
Computational Fluid Dynamics (CFD) simulations will be performed for the direct-contact condensation and thermal stratification experiments of LUT. The simulations will be done by using the commercial ANSYS Fluent code. The EHS/EMS models developed at KTH will be implemented in the Fluent code by using user-defined functions. In the model, the sparger of the vent pipe in the pressure suppression pool will be described with mass, heat and momentum sources. In 2019, simulations of stratification and mixing experiments performed with the PPOOLEX facility will be performed with the Fluent code. The results will be compared to the experiments of LUT and to the results calculated by KTH. In addition, possibilities to implement an approach based on the EHS/EMS model in the Apros system code will be studied. In 2020–2021, CFD calculations will be performed to validate the implemented EHS/EMS model for stratification and mixing. In addition, the implementation of the approaches based on the EHS/EMS model in the Apros system code will be tested.