Development and implementation of effective models in GOTHIC for the prediction of mixing and thermal stratification in a BWR pressure suppression pool
2011 (English)In: Proceedings of the 2011 international congress on advances in nuclear power plants: ICAPP2011, American Nuclear Society, 2011Conference paper (Refereed)
As a passive safety system, the function of steam suppression pools in a BWR plant isparamount to the containment performance. The pressure suppression pool wasdesigned to have the capability as a heat sink to cool and condense steam releasedfrom the core vessel and/or main steam line during loss of coolant accident (LOCA)or opening of safety relief valve in normal operation of BWRs. For the case of smallflow rates of steam influx, thermal stratification could develop on the part aboveblowdown pipe exit and significantly impede the pool’s pressure suppression capacity.During a steam blowdown, the steam condenses rapidly in the pool and the hotcondensate rises in a narrow plume above steam injection plane and spreads into athin layer at the pool’s free surface. The increasing temperature of the surfacedefining the steam partial pressure in the vapor space causes increment ofcontainment pressure. Once steam flow rate increases significantly, momentumintroduced by the steam injection and/or periodic expansion and shrink of large steambubbles due to direct contact condensation can destroy stratified layers and lead tomixing of the pool water.Accurate and computationally efficient prediction of the pool thermal-hydraulics inthe scenarios with transition between thermal stratification and mixing, presents acomputational challenge. Lumped parameter codes have no capability to predicttemperature distribution of water pool during thermal stratification development.Scaling approaches and 1D codes generally have a lack of ability to capture historyeffects in complex plant transients, while high-order-accurate CFD (RANS, LES)methods are not practical due to excessive computing power needed to calculate 3Dhigh-Rayleigh-number natural circulation flow in long transients.In this paper we discuss a middle ground approach to modeling of mixing and thermalstratification development during steam injection in a tank of water. The approachemploys GOTHIC containment code as a computational vehicle which has features ofboth 1D/lumped parameter models for description of plant thermal hydraulic systemand CFD-like models for prediction of distributed parameters in the pool. The effectof steam injection on the mixing and stratification is provided by the effective heatsource (EHS) model and the effective momentum source (EMS) model. Proposedmodels are based on the experimental observations and analysis which suggest thatthe heat flux through the blowdown pipe and the momentum out of the pipe outlet aretwo driving factors which affect stratification and mixing process. The EMS modelprovides the effect of steam injection in terms of momentum responsible forestablishment of large scale circulation in the pool, while the aim of the EHS model isto simulate the thermal effect of steam injection by the effective heat transferred to thepool. The POOLEX experimental facility (Lappeenranta University of Technology inFinland) data is used to develop and validate the EHS and EMS models. Thecomparison of simulation results to experimental data are discussed in the paper.
Place, publisher, year, edition, pages
American Nuclear Society, 2011.
IdentifiersURN: urn:nbn:se:kth:diva-53589OAI: oai:DiVA.org:kth-53589DiVA: diva2:470387
2011 International congress on advances in nuclear power plants - ICAPP 2011, Nice, France, 2-5 May, 2011
QC 201203302011-12-282011-12-282012-03-30Bibliographically approved