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Pool Stratification and Mixing Induced by Steam Injection through Spargers: CFD modelling of the PPOOLEX and PANDA experiments
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
Paul Scherrer Institute (PSI), Switzerland.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Spargers are multi-hole injection pipes used in Boiling Water Reactors (BWR) and Advanced Pressurized (AP) reactors to condense steam in large water pools. During the steam injection, high pool surface temperatures induced by thermal stratification can lead to higher containment pressures compared with completely mixed pool conditions, the former posing a threat for plant safety. The Effective Heat Source (EHS) and Effective Momentum Source (EMS) models were previously developed and validated for the modelling of a steam injection through blowdown pipes. The goal of this paper is to extend the EHS/EMS model capabilities towards steam injection through multi-hole spargers. The models were implemented in the CFD code of ANSYS Fluent 17.0 and calibrated against the PPOOLEX and PANDA experiments with spargers analysed by the authors in [1] (Gallego-Marcos, I., et al., 2018). Modelling guidelines are established for the adequate simulation of the pool behaviour. A new correlation is proposed to model the turbulent production and dissipation caused by buoyancy. Sensitivity studies addressing the effect of different assumptions on the effective momentum magnitude, profile, angle and turbulence are presented. Calibration of the momentum magnitude showed that it varies between 0.2 to 1.2 times the steam momentum at the injection holes. Differences of this fraction between the PPOOLEX and PANDA simulations are discussed. Analysis of the calculated flow above the cold stratified layer shows that the erosion of the layer is induced by the action of turbulence rather than mean shear flow.

Keywords [en]
Thermocline, turbulence production buoyancy, Richardson, C3e coefficient, oscillatory bubble regime.
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-238714OAI: oai:DiVA.org:kth-238714DiVA, id: diva2:1261888
Note

QC 20180911

Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-09Bibliographically approved
In thesis
1. Steam condensation in a water pool and its effect on thermal stratification and mixing
Open this publication in new window or tab >>Steam condensation in a water pool and its effect on thermal stratification and mixing
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Pressure Suppression Pool (PSP) of a Boiling Water Reactor (BWR) is a large heat sink designed to limit the containment pressure by condensing steam released from the primary coolant system. The development of thermal stratification is a safety concern since it leads to higher containment pressures than in completely mixed conditions, and can affect the performance of systems such as the emergency core cooling and containment spray, which the use PSP as a source of water.The goal of this thesis is to develop and validate models for the prediction of the PSP behavior during a steam injection in a Nordic BWR. The framework of the Effective Heat Source and Effective Momentum Source (EHS/EMS) models is used to provide the integral heat and momentum sources induced by the steam condensation. The EHS/EMS can be implemented in a containment thermal-hydraulic or a CFD code, where the pool is modelled with a single-phase liquid solver.EHS/EMS models are developed for the low steam mass flux regimes appearing in (i) large diameter blowdown pipes connecting the drywell to the wetwell pool; and (ii) multi-hole sparger pipes connecting the primary system to the pool.Empirical correlations are developed to predict the effective momentum induced by chugging in the blowdown pipes. The correlations are implemented in GOTHIC, where a containment model is proposed to enable capturing the feedback between pool conditions and drywell pressure. Validation is performed against the PPOOLEX experiments.Conceptual designs are proposed for a set of large-scale pool experiments with spargers in the PPOOLEX and PANDA facilities. Correlations are proposed for the erosion velocity of a cold layer, and ranges are estimated for the angle, profile and turbulence of the momentum sources created by steam injection. CFD simulations of the experiments is done to calibrate the momentum sources in the oscillatory bubble regimes. A concept of the Separate Effect Facility (SEF) is proposed to provide a measurements of the effective momentum. Empirical correlations for the bubble radius, velocity, heat transfer coefficient, etc. are also developed and compared to available data from the literature.Application of the developed CFD and EHS/EMS models to full-scale containment behavior shows that thermal stratification can occur during prototypic steam injection conditions. Recommendations are given on how to avoid this.

Place, publisher, year, edition, pages
Sweden: KTH Royal Institute of Technology, 2018. p. 69
Series
TRITA-SCI-FOU ; 2018:48
Keywords
Steam injection, EHS/EMS, blowdown pipes, spargers, chugging, oscillatory bubble, CFD, condensation pool, stratification, mixing
National Category
Energy Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-238732 (URN)978-91-7873-028-5 (ISBN)
Public defence
2018-12-07, FB54, AlbaNova University Centre, Rogslagstullbacken 21, 114 21 Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Swedish Radiation Safety Authority
Note

QC 20181109

Available from: 2018-11-09 Created: 2018-11-09 Last updated: 2018-11-12Bibliographically approved

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