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Thermal Stratification and Mixing in a Nordic BWR Pressure Suppression Pool
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The pressure suppression pool of a Nordic Boiling Water Reactor (BWR) serves as a heat sink to condense steam from the primary coolant system in normal operation and accident conditions. Thermal stratification can develop in the pool when buoyancy forces overcome the momentum created by the steam injection. In this case, hot condensate forms a hot layer at the top of the pool, reducing the pool cooling and condensation capacity compared to mixed conditions. The Effective Heat Source and Effective Momentum Source (EHS/EMS) models were previously proposed to model the large-scale pool behavior during a steam injection. In this work, we use CFD code of ANSYS Fluent with the EHS/EMS models to simulate the transient behavior of a Nordic BWR pool during a steam injection through spargers. First, a validation against a Nordic BWR pool test is presented. Prediction of the pool behavior for other possible injection scenarios show that stratification can occur at prototypic steam injection conditions, and that the hot layer temperature above the injection point can be non-uniform. In cases with significant steam condensation inside the sparger pipes, the 95 oC pool temperature limit for the Emergency Core Cooling System (ECCS) pumps was reached ~7 h after the beginning of the blowdown.

Keywords [en]
Sparger; relief vales; steam injection; condensation; CFD; effective momentum
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-238705OAI: oai:DiVA.org:kth-238705DiVA, id: diva2:1261784
Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-12Bibliographically 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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Gallego-Marcos, IgnacioGrishchenko, DmitryKudinov, Pavel

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