Prsentation PowerPoint

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• Simulation of
• Molten Corium Concrete Interaction
• in a Stratified Configuration
• the COMET-L2-L3 Benchmark

Bertrand SPINDLER, CEA, Grenoble Kresna ATKHEN,
EDF, Villeurbanne Michel CRANGA, IRSN,
Cadarache Jerzy FOIT, FZK, Karlsruhe Monica
GARCIA MARTIN, UPM, Madrid Werner SCHMIDT, AREVA,
Erlangen Tuomo SEVON, VTT, Espoo Claus SPENGLER,
GRS, Cologne
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Late phase of MCCI stratified configuration

• Molten Corium Concrete Interaction (MCCI)
• In some scenarios of Severe Accident, corium is
  assumed to spread over the concrete basemat of
  the reactor pit
• Ablation of the concrete occurs, with complex
  phenomena of thermohydraulics and
  physico-chemistry MCCI
• Investigations concerning MCCI are still going on
• Late phase of MCCI
• Decrease of the ablation rate due to
• the decrease of the residual power
• the increase of the heat transfer areas
• Decrease of the gas flow rate issued from the
  concrete decomposition
• Decrease of the oxide phase density due to light
  oxides from the concrete decomposition
• Stratified configuration is expected
• Metal phase at the bottom (mainly Fe, Cr, Ni)
• Oxide phase at the top (mainly UO2, ZrO2, SiO2,
  CaO, Al2O3)

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Late phase of MCCI stratified configuration

• Stratified configuration
• Main uncertainty heat transfer between the two
  layers
• Consequence axial and radial ablation rates not
  well known
• Few experimental programs
• The BETA test at FZK with a large test matrix
• New tests at FZK COMET-L2 and COMET-L3
• The COMET-L2-L3 benchmark
• COMET-L2 as for post-test simulation
• COMET-L3 for blind test simulation

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The COMET-L2-L3 benchmark

• Frame
• SARNET WP 11.2 Molten corium concrete/ceramic
  interaction
• Participants
• CEA, AREVA, EDF, FZK, GRS, IRSN, UPM, VTT
• Schedule
• COMET-L2 March to August 2006
• COMET-L3 September 2006 to January 2007
• Only 1.5 month delay at the end
• Planned final meeting canceled

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COMET-L2, -L3 tests

• MCCI tests at FZK
• Stratified oxide-metal configuration with metal
  at the bottom
• Input power in the metal layer (induction
  heating)
• No input power in the oxide layer
• COMET-L2
• February 2005
• Used for post-test simulations
• COMET-L3
• November 2005
• More oxide, higher heat flux, than COMET-L2
• Water aspersion after a first period of dry
  erosion
• Used for blind simulations

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COMET-L2, -L3 tests
Scheme of the facility and of the concrete test
section
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COMET-L2, -L3 tests
Scheme of the thermocouples instrumentation in
the plane NW-SE
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COMET-L2 test
430 kg metal 90 Fe, 10 Ni 35 kg oxide 56
Al2O3, 44 CaO Mean power 200 kW Initial
temperature 2023 K Power off after 1015 s
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COMET-L3 test
425 kg metal 90 Fe, 10 Ni 211 kg oxide 56
Al2O3, 44 CaO Mean power 220 kW Initial
temperature 1940 K Top flooding at 800 s Power
off after 1878 s
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COMET-L2, -L3 tests

• Initial period of about 100 s until end of
  initial overheat, with isotropic ablation
• Steady state regime with faster axial ablation
  rate
• Agreement with the results of the BETA tests
• COMET-L3 low influence of flooding

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COMET-L2, -L3 benchmark

• Participants and code
• AREVA with COSACO
• CEA with TOLBIAC-ICB (base case and
  modifications)
• EDF with TOLBIAC-ICB
• FZK with WECHSL
• GRS with MEDICIS and with WEX
• IRSN with MEDICIS (base case and modifications)
• UPM with MELCOR (COMET-L3 only)
• VTT with MELCOR
• Same input data
• Models depending of the codes

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COMET-L2 post test simulations

• Metal temperature versus time (no measurements
  for comparison)

initial period with overheat
power off
Large dispersion (150 K), but 6 results between
1750 and 1780 K
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COMET-L2 post test simulations

• Oxide temperature versus time (no measurements
  for comparison)

Large dispersion 450 K at 1000 s
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COMET-L2 post test simulations

• Axial ablation depth versus time

Experiment no symetry
steady state regime
initial period with overheat
Large dispersion in the initial period Similar
ablation rate in the steady state regime Maximum
ablation depth underestimated
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COMET-L2 post test simulations

• Radial ablation depth versus time

Radial ablation depth overestimated
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COMET-L2 post test simulations
Final shape of the cavity
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COMET-L3 blind simulations

• Metal temperature versus time (no measurements
  for comparison)

initial period with overheat
power off
Lower dispersion compared to COMET-L2
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COMET-L3 blind simulations

• Oxide temperature versus time

Lower dispersion compared to COMET-L2
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COMET-L3 blind simulations

• Top surface temperature versus time, with
  measurement

top flooding
Before flooding dispersion 800 K
measurements in between the calculations
After flooding dispersion 1500 K only one
code at water temperature
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COMET-L3 blind simulations

• Heat flux density from metal to oxide layer
  versus time

• Initial phase positive or negative
• Steady state before flooding positive
• After flooding positive or negative

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COMET-L3 blind simulations

• Heat flux density at the top surface

top flooding
Flooding effet very different depending on the
code
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COMET-L3 blind simulations

• Cumulated hydrogen production versus time

Factor 5 between the final minimum and maximum
results
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COMET-L3 blind simulations

• Axial ablation depth versus time

Less dispersion than for COMET-L2
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COMET-L3 blind simulations

• Radial ablation depth versus time

Overestimation, or in agreement with the
measurements
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COMET-L3 blind simulations
Final shape of the cavity
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Overview of the codes and models

• COSACO by AREVA
• Crust formation and solidification in the pool
  for oxide
• Coupling with CHEMAPP for physico-chemistry
• Heat transfer with slag layer for metal
• Isotropic heat flux distribution
• MEDICIS in ASTEC by IRSN
• Pool-crust interface temperature between solidus
  and liquidus
• IRSN close to liquidus GRS solidus
• Heat transfer with slag layer
• Greene correlation for heat transfer between the
  two layers
• Multiplying factor for radial heat transfer
  (IRSN)
• MELCOR by Sandia National Laboratory
• Pool-crust interface temperature is solidus
  temperature
• Heat transfer with slag layer
• Greene correlation for heat transfer between the
  two layers

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Overview of the codes and models

• TOLBIAC-ICB by CEA
• Phase segregation model with pool-crust
  interfacial temperature equal to liquidus
  temperature
• Coupling with GEMINI code for physico-chemistry
• Reference isotropic heat flux distribution
• Multiplying factor for radial heat transfer
  (COMET-L2-L3)
• WECHSL by FZK
• Heat transfer with film or bubble or transition
  model
• Crusts at the interfaces
• Heat transfer between the two layers with a
  correlation by Haberstroh and Reinders modified
  for gas percolation
• WEX in ASTEC by GRS
• Modified version of WECHSL
• Different empirical fitting of the heat transfer
  models

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Summary

• Large scatter of the code results for the
  different variables
• Large scatter for the same code by different
  users with different models
• Very different behavior of the heat transfer
  between the two layers
• MCCI phenomena still not well understood
• Results specific to the COMET-L2-L3
  configuration ?
• Consequences of these uncertainties on reactor
  cases ?
• Next step for an answer to theses questions
• new benchmark proposed in the frame of SARNET
• for reactor cases