INSTAB - VTT

INSTABCouplings and instabilities in reactor systems

Markku Puustinen, Jani Laine, Antti Räsänen, Lauri Pyy,Eetu Kotro, Vesa Tanskanen, Elina Hujala

Lappeenranta University of Technology

SAFIR2018 Interim Seminar, March 23-24, 2017, Espoo

INSTAB – Motivation

Condensation pool is an in-containment heatsink in BWRsSteam discharges are received fromsafety/relief valves and blowdown pipesWater discharge from containment spray andResidual Heat Removal (RHR) return lines

Thermal stratification of the condensationpool limits the volume of water absorbingheat• Full capacity of the pool not used

containment overpressure risk

The INSTAB project studies the stability ofstratification and mixing mechanisms in pool

SAFIR2018 Interim Seminar 3

Upper dry well

Blowdown pipes

Lower dry well

Wet well

INSTAB – Enhancement of safety

Earlier LUT POOLEX and PPOOLEX projects have addressedthe blowdown pipe performance• direct contact condensation (DCC) leads to instability –

chugging – which causes large dynamic mechanical loads

INSTAB focus in 2015-2016 has been on• modelling of stratification and mixing in relation to operation

of Safety/Relief Valve (SRV) spargers and Residual HeatRemoval (RHR) nozzles

• supporting the development of the Effective Heat Source(EHS) and Effective Momentum Source (EMS) models,originally developed by KTH• already successfully developed for blowdown pipes

• supporting CFD code modelling of direct contactcondensation situations at LUT and VTT


INSTAB – PPOOLEX test facility

Height 7.45 m, diameter 2.4 m,volume 31 m3

• Max pressure 0.5 MPa• Steam from the nearby PACTEL

facility (1 MW)

Pressure, differential pressure,temperature, flow, strain and relativehumidity measurements• kHz range measurements and data

acquisitionTriple high speed camera and stereoParticle Imaging Velocimetry (PIV)systems


INSTAB – Sparger tests: stratification erodes awayPool water above sparger “mouth” warms up ~uniformlySimultaneously, the thermocline moves downwardsNo chugging, condensation of small steam jetsComplete mixing of the water pool through an erosion processwas achieved in the end


INSTAB – Erosion is due to large-scale turbulence


Flow field in the vicinity of thethermocline can be resolvedby PIVLarge eddies exist around theelevation of the thermocline

INSTAB – Direct Contact Condensation modeldevelopment with NEPTUNE_CFD

CFD modelling of DCC requires that the interfacial area densitybetween the liquid and vapour phases is resolved• either by using a very dense computational grid, or• by applying a special interfacial instability modelInterfacial area density has been modelled in the NEPTUNE_CFDcode with the help of a plausible and simple solution of Rayleigh-Taylor instability (RTI), originally introduced by Pellegrini et al.• The model seems to perform qualitatively well enough


Simulations of a plexiglass blowdownpipe case in PPOOLEX have beendone in order to further investigate theeffect of the RTI model on calculationresults of DCC

INSTAB – Highlights from CFD calculations

The condensation rate is higher and the shapes of fully expanded bubbles aredifferent in the case with the Rayleigh-Taylor instability model (left) compared to thecase without it (right)

• In general the RTI model seems to give results closer to reality with a lowresolution mesh


INSTAB – Pressure data interpretation

Pressure data from earlierPPOOLEX tests were fastFourier transformed (FFT) andcompared to the bubbleoscillation results of theNEPTUNE_CFD simulationsIt is possible to identify fromthe test data frequenciescaused by the blowdown pipe,test vessel and bubblesthemselvesThis helps DCC modellersfocus on reproducing bubblecondensation correctly


Frequency in FFT [Hz] Possible source of frequency0.5–3.5 chugging frequency11–12 vessel41–45 natural frequency of the bubble80–83 vessel150 vessel

250–300 bubble/blowdown pipe

INSTAB – Highlights from RHR nozzle tests

To obtain data for extending the EMS and EHS models toRHR system nozzles a series of tests was done inPPOOLEX

The effects of nozzle orientation, T in the pool, injectionwater temperature and injection water mass flow rate onmixing efficiency were studied• Thermally stratified condition was created by injecting

steam into the pool water via the sparger pipe• Two regions with clearly different water

temperatures and a narrow thermocline regionbetween them developed in the pool

Compete mixing was achieved with the horizontalorientation of the RHR nozzle


INSTAB – Highlights from RHR nozzle tests

With the vertical orientation of the RHR nozzle mixing was otherwise successfulbut incomplete above the nozzle elevation


INSTAB – CONCLUSIONS

INSTAB tests have generated a large database onsuppression pool phenomena• Data on stability of pool stratification and

efficiency of pool as heat sink• Strong contribution to the development of the

EMS and EHS models for blowdown pipes,SRV spargers and RHR nozzles

DCC modelling in CFD (Fluent, NEPTUNE_CFD, OpenFOAM) evaluated onthe basis of the PPOOLEX tests• Rayleigh-Taylor instability modelling for the interface is very promising

Closures for the EMS/EHS models: in 2017-2018,• PPOOLEX spray tests will be conducted• separate effect tests, where momentum induced by steam injection through

a sparger is measured directly


Thank you for your attention


INSTAB – Plans for steam jet testing

In 2017, a separate effect test facility will beconstructed and momentum created by steamdischarge through sparger holes will be measureddirectly in order to provide closures for the EMSmodel development work for spargers

Once the EMS and EHS models have beenvalidated for spargers, they can be implementedalso to other codes than GOTHIC


Flexible junction

Pipe fixed and allowed torotate around this point

Steaminjection

Forcemeasurements

~1000

~500

Open ceiling

~300

INSTAB - VTT

Documents

Transcript of INSTAB - VTT