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Steam condensation in a water pool and its effect on thermal stratification and mixing
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.ORCID iD: 0000-0002-5794-2651
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 [en]
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: urn:nbn:se:kth:diva-238732ISBN: 978-91-7873-028-5 (print)OAI: oai:DiVA.org:kth-238732DiVA, id: diva2:1261953
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
List of papers
1. Modelling of pool stratification and mixing induced by steam injectionthrough blowdown pipes
Open this publication in new window or tab >>Modelling of pool stratification and mixing induced by steam injectionthrough blowdown pipes
2018 (English)In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 112, p. 624-639Article in journal (Refereed) Published
Abstract [en]

Containment overpressure is prevented in a Boiling Water Reactor (BWR) by condensing steam into thepressure suppression pool. Steam condensation is a source of heat and momentum. Competition betweenthese sources results in thermal stratification or mixing of the pool. The interplay between the sources isdetermined by the condensation regime, steam mass flow rate and pool dimensions. Thermal stratificationis a safety issue since it limits the condensing capacity of the pool and leads to higher containmentpressures in comparison to a completely mixed pool with the same average temperature. The EffectiveHeat Source (EHS) and Effective Momentum Source (EMS) models were previously developed for predictingthe macroscopic effect of steam injection and direct contact condensation phenomena on the developmentof stratification and mixing in the pool. The models provide the effective heat and momentumsources, depending on the condensation regimes. In this work we present further development of theEHS/EMS models and their implementation in the GOTHIC code for the analysis of steam injection intocontainment drywell and venting into the wetwell through the blowdown pipes. Based on thePPOOLEX experiments performed in Lappeenranta University of Technology (LUT), correlations arederived to estimate the steam condensation regime and effective heat and momentum sources as functionsof the pool and steam injection conditions. The focus is on the low steam mass flux regimes withcomplete condensation inside the blowdown pipe or chugging. Validation of the developed methodswas carried out against the PPOOLEX MIX-04 and MIX-06 tests, which showed a very good agreementbetween experimental and simulation data on the pool temperature distribution and containmentpressure.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
thermal stratification, GOTHIC, chugging, frequency and amplitude, time average, effective momentum source
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-217309 (URN)10.1016/j.anucene.2017.10.019 (DOI)000419409100053 ()2-s2.0-85032947808 (Scopus ID)
Note

QC 20171108

Available from: 2017-11-07 Created: 2017-11-07 Last updated: 2018-11-09Bibliographically approved
2. Pool stratification and mixing during a steam injection through spargers: analysis of the PPOOLEX and PANDA experiments
Open this publication in new window or tab >>Pool stratification and mixing during a steam injection through spargers: analysis of the PPOOLEX and PANDA experiments
Show others...
2018 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 337, p. 300-316Article in journal (Refereed) Published
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. A steam injection induces heat, momentum and mass sources that depend on the steam injection conditions and can result in thermal stratification or mixing of the pool. Thermal stratification reduces the steam condensation capacity of the pool, increases the pool surface temperature and thus the containment pressure. Development of models with predictive capabilities requires the understanding of basic phenomena that govern the behavior of the complex multi-scale system. The goals of this work are (i) to analyze and interpret the experiments on steam injection into a pool through spargers performed in the large-scale facilities of PPOOLEX and PANDA, and (ii) to discuss possible modelling approaches for the observed phenomena. A scaling approach was developed to address the most important physical phenomena and regimes relevant to prototypic plant conditions. The focus of the tests was on the low steam mass flux and oscillatory bubble condensation regimes, which are expected during a long-term steam injection transient, e.g. in the case of a Station Black Out (SBO). Exploratory tests were also done for chugging and stable jet conditions. The results showed a similar behavior in PPOOLEX and PANDA in terms of jet induced by steam condensation, pool stratification, and development of hot layer and erosion of the cold one. A correlation using the Richardson number is proposed to model the erosion rate of the cold layer as a function of the pool dimensions and steam injection conditions.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Pool stratification, Oscillatory bubble, Thermocline erosion, Richardson, Turbulence, Chugging
National Category
Energy Systems
Identifiers
urn:nbn:se:kth:diva-232461 (URN)10.1016/j.nucengdes.2018.07.004 (DOI)000441759300026 ()2-s2.0-85050149931 (Scopus ID)
Funder
Swedish Radiation Safety Authority
Note

QC 20180822

Available from: 2018-07-23 Created: 2018-07-23 Last updated: 2018-11-09Bibliographically approved
3. Pool Stratification and Mixing Induced by Steam Injection through Spargers: CFD modelling of the PPOOLEX and PANDA experiments
Open this publication in new window or tab >>Pool Stratification and Mixing Induced by Steam Injection through Spargers: CFD modelling of the PPOOLEX and PANDA experiments
Show others...
(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
Thermocline, turbulence production buoyancy, Richardson, C3e coefficient, oscillatory bubble regime.
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-238714 (URN)
Note

QC 20180911

Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-09Bibliographically approved
4. Effective momentum induced by steam condensation in the oscillatory bubble regime
Open this publication in new window or tab >>Effective momentum induced by steam condensation in the oscillatory bubble regime
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The spargers used in Boiling Water Reactors (BWR) discharge steam from the primary coolant system into a pool of water. Direct steam condensation in subcooled water creates sources of heat and momentum determined by the condensation regimes, called “effective sources” in this work. Competition between the effective sources can result in thermally stratification or mixing of the pool. Thermal stratification is a safety concern in BWRs since it reduces the steam condensation and pressure suppression capacity of the pool. In this work, we present semi-empirical correlations to predict the effective momentum induced by steam condensation in the oscillatory bubble regime, relevant for the operation of spargers in BWRs. A Separate Effect Facility (SEF) was designed and built at LUT, Finland, in order to provide the necessary data. An empirical correlation for the effective momentum as a function of the Jakob number is proposed. The Kelvin Impulse theory was also applied to estimate the effective momentum based on information about the bubble dynamics. To do this, new correlations for the bubble collapse frequencies, maximum bubble radius, velocities, pressure gradient and heat transfer coefficient are proposed and compared to available data from the literature. The effective momentum induced by sonic steam jets appears to be constant in a wide range of studied Jakob number. However, further experimental data is necessary at larger Jakob numbers and steam mass fluxes.

Keywords
Effective momentum; Kelvin Impulse; bubble radius; collapsing frequency; heat transfer coefficient
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-238704 (URN)
Note

QC 20181109

Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-12Bibliographically approved
5. Thermal Stratification and Mixing in a Nordic BWR Pressure Suppression Pool
Open this publication in new window or tab >>Thermal Stratification and Mixing in a Nordic BWR Pressure Suppression Pool
(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
Sparger; relief vales; steam injection; condensation; CFD; effective momentum
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-238705 (URN)
Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-12Bibliographically approved

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