Accident Management Issues within the ARTIST Project

Paul Scherrer Institut • CH-5232 Villigen PSI • LTH SAMI_2001 / 20.04.23 / DA42

PAUL SCHERRER INSTITUT

Accident Management Issues within the ARTIST Project

S. Güntay, S. Güntay, A. DehbiA. Dehbi, D. Suckow, J. Birchley, D. Suckow, J. Birchley

Laboratory for Thermal-HydraulicsPaul Scherrer Institut Villigen, Switzerland

OECD Workshop on the Implementation of Severe Accident Management Measures

Villigen, SwitzerlandSeptember 13, 2001



Motivation behind ARTIST Project

– ARTIST: Aerosol Trapping in Steam Generator

– No credit given for FP retention in secondary side of a SG.

– Up to now: only one large scale SGTR experiment at Westinghouse: droplet carryover in DBA-type accident.

– Theoretical & laboratory-scale separate effect experiments:

evidence of high aerosol removal in SGTR due to:

• Turbulent deposition inside ruptured tube• Inertial & turbulent impaction on secondary structures• Thermophoresis between hot gas and colder walls• Condensation-diffusiophoresis in water pool



Expected DF‘s according to Available Simple Models and Experiments

Location

DF Uncertainty

Inside 0.3 m tube

3 Not known

Inside 1 m tube

10 Not known

In SG break stage

10-60 Not known

In SG far field bundle

3-10 Not known

Separator

Not known Not known

Dryer

Not known Not known

Flooded bundle, 4 m

20 50%



Scaling of SG Bundle Size using CFD

• Computational Fluid Dynamics (CFD) simulations conducted to:

– Estimate momentum dissipation near break– Decide on ARTIST bundle size (large enough number of tubes &

economically feasible)

• Simulation conducted with 3 types of breaks (fish-mouth, axisymmetric)

• Results:– Velocity drops by > 1 order of magnitude after 5 tube rows– Thus: momentum dissipation and aerosol removal in vicinity of

break can be reproduced in ARTIST 1 to 1.

• Pictures (1,2)



Main Geometric Parameters in ARTIST

Parameter Unit Beznau ARTIST

Number of tubes - 3238 (U tube) 264(staight)

Number of dryers - 12 1

Number of separators - 12 1

Max. tube length m 9.0 3.8

Tube ID mm 16.7 16.7

Surface/volume ratio m2/m3 102.2 87.2

Porosity - 0.67 0.71



ARTIST Consortium ExperimentsARTIST Consortium Experiments

• ARTIST: International project – Running time: 2003-2007– Many potential partners: NRC, AVN, IPSN, FRAMATOME-ANP,

CSN, HSK, Skidpower, etc.

• 7 Phases, addressing fission product retention in – Severe accidents (aerosols) – DBA (droplets)



ARTIST Consortium (cont‘d)ARTIST Consortium (cont‘d)

• Phase I: In-tube aerosol retention. Sonic flows. Velocities in tube: 200-300 m/s.

• Phase II: Aerosol retention in bundle break stage, dry conditions. Sonic flows. Velocities at exit of break: 200-300 m/s

• Phase III: Retention in bundle far-field, dry conditions. Impaction & thermophoresis. Low velocities: 0.1-1 m/s.

• Phase IV: Aerosol retention in separator & dryer. Small velocities, less than 1 m/s.



ARTIST Consortium (cont‘d)ARTIST Consortium (cont‘d)

• Phase V: Aerosol retention in flooded bundle.

• Phase VI: Droplet retention in separator & dryer. DBA-type experiment.

• Phase VII: Integral tests. Retention in the whole SG



Selected SAM Issues in ARTIST

• ARTIST facility also suitable for particular AM issues

• Two sets of issues identified so far:

– Impact of water level on droplet formation at the water pool surface (size, flux of droplet flow)

– Potential for more accurate determination of

• Break location

• Water level in the SG.



Droplet Generation at Pool Surface

• AM in SGTR involves flooding SG to scrub aerosols

• Gas bubbling in SG pool creates droplet flow new source of release

• Retention in separator & dryer depends on droplet inertia importance of droplet size

• Droplet size, flux determined by flow regime upstream of water surface

– Turbulent flow large drops easier to retain

– Bubbly flow small drops harder to retain

• Aerosol vs. droplet retention? conflicting goals. Need for optimization.



Droplet Generation at Pool Surface (cont‘d)

• With high water level:

– Bubbly flow at surface

– small bubbles

– small droplets

• Net effects:– High aerosol retention in pool– High droplet source to

separator and dryer

DropletAerosol

Gas




• With low water level

– Turbulent gas flow at surface

– Large bubbles

– Large droplets

• Net effects:– Low aerosol retention in pool– Low droplet source to

separator and dryer

DropletAerosol

Gas




• Proposed experiment: – Determine drop size & flux as function of:

• Water level

• Gas flow rate

– Determine effect of support plate on droplet size & flux

• Main objective of experiment: characterize optimum flooding level which minimizes source due to:– Aerosols

– Droplets



Break & Water Level Determination

• Current practice: following SGTR, flooding up to 2/3 of separator (assumption: break at U bend, for lack of better guess)

• Level estimated by wide-range p measurement of collapsed level

• Uncertainty of 1 m on water level. Large. Need to preclude overfilling with potential leakage through SRV

• Investigations in ARTIST proposed on following topics (related):– Determination of break level

– Reduction in water level uncertainty



Break & Water Level Determination (cont‘n)

• Proposed experiment:– Gas discharge from a break in ARTIST

– Vary: break location, flow rate, water level

– Pressure measurement taken along flooded bundle

– Determine correlation between break location & p profile

• Once correlation between break location & p is found, correlate water level in the bundle versus:– Break flow rate

– Break location– Collapsed water level

• Objective of experiment: reduce uncertainty on water level estimation.



Summary• ARTIST: wide-ranging project which addresses key safety issues in

SGTR

• Strong international interest and participation

• ARTIST-Consortium experiments (2003-2007): 7 phase project, dealing with aerosol/droplet retention. Separate effects & integral tests.

• Possibility to use ARTIST for further AM tests. Potential test matrix proposes investigation in two directions:

– Determination of optimum flooding level to minimize source due to aerosol+ droplets

– Lowering uncertainty on water level estimation in SGTR events

Documents

Accident Management Issues within the ARTIST Project