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Parametrical study on MCCI reactor cases under dry cavity conditions forassessment of parameters of importancePhilippe Dejardin

ERMSAR 2012, Cologne March 21 – 23, 2012

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TABLE OF CONTENT

• Objectives and methodology

• Cases definitions, results and findings- Base cases & foreseen parametric cases

- Additional parametric cases

• Conclusions and recommendations

22 03 12Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importanceSession 4 “Ex-vessel corium behaviour” – Paper 4.4


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TABLE OF CONTENT







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OBJECTIVES & METHODOLOGY

• Objectives- Derive parameters of importance for reactor cases under dry MCCI conditions

- Achievement of clear conclusions and recommendations for future work

- Contribution to the international effort

• Methodology- Use of the ASTEC / MEDICIS module in stand-alone

- Definition of a parametric study considering both siliceous and limestone-common-sand concretes types under dry cavity conditions

- Base cases + several foreseen parametric cases investigating 3 axes of interest• Intrinsic initial parameters of the reactor cavity

• Scenario-dependent parameters affecting the initial state of the MCCI

• Physical model parameters involved in some MCCI phenomena


Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance

Session 4 “Ex-vessel corium behaviour” – Paper 4.4 22 03 12

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TABLE OF CONTENT







Concrete compositio

n

SIL LCS

Al203 2.66% 2.54%

CaO 9.97% 35.31%

CO2 0.81% 22.51%

H2O 9.58% 7.54%

SiO2 76.98%

32.10%

Corium compositio

n

Masses [T]

UO2 80.0

ZrO2 16.2

Zr 8.0

Fe 14.2

Cr 3.4

Ni 2.4

3.0 m

9.0 m

3.5 m

Z

r

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REACTOR CASES - BASE CASE / DEFINITION

• Cavity geometry and concrete composition

• Corium initial conditions- 80 tons UO2 / 20 tons Zr (60% ox.) / 20 tons stainless steel

- Stratified initial configuration with initial temperature = 2400°C• Solid oxide layer at the bottom / Liquid metal layer at the top

• Boundary conditions- Decay heat evolution with MCCI onset 1.5 h after SCRAM

- Constant cavity environment: 1700°C / 1.5 bar abs

• Physical model parameters- Stratification evolution parameter: b_HS = 0.027 m/s

- γ = 0.2 T_solidif = 0.2 T_solidus + 0.8 T_liquidus



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FORESEEN PARAMETRIC CASES - DEFINITIONS

CaseInitial cavity parameters Scenario dependent parameters

Physical model parametersconcrete geometry corium composition boundary conditions

type density T_abla Δh_abla radiusstainless steel mass

ZrO2/Zr oxidation

ratio

cavity temperature

delay between

SCRAM and MCCI

b_HS gamma

[kg/m^3] [K] [J/kg] [m] [tons] [%] [K] [h]

[BC] SIL 2436 1570 1.95E+06 3.0 20 60 1700 1.5 0.027 0.2

[P1] SIL 2436 1570 1.95E+06 2.0 20 60 1700 1.5 0.027 0.2

[P2] SIL 2436 1570 1.95E+06 3.0 30 60 1700 1.5 0.027 0.2

[P3] SIL 2436 1570 1.95E+06 3.0 20 30 1700 1.5 0.027 0.2

[P4] SIL 2436 1570 1.95E+06 3.0 20 90 1700 1.5 0.027 0.2

[P5] SIL 2436 1570 1.95E+06 3.0 20 60 1500 1.5 0.027 0.2

[P6] SIL 2436 1570 1.95E+06 3.0 20 60 1200 1.5 0.027 0.2

[P7] SIL 2436 1570 1.95E+06 3.0 20 60 1700 5.0 0.027 0.2

[P8] SIL 2436 1570 1.95E+06 3.0 20 60 1700 10.0 0.027 0.2

[P9] SIL 2436 1570 1.95E+06 3.0 20 60 1700 1.5 0.018 0.2

[P10] SIL 2436 1570 1.95E+06 3.0 20 60 1700 1.5 0.054 0.2

[P11] SIL 2436 1570 1.95E+06 3.0 20 60 1700 1.5 0.027 0.0

[P12] SIL 2436 1570 1.95E+06 3.0 20 60 1700 1.5 0.027 0.5

• Calculation matrix – SIL concrete



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BASE CASES & FORESEEN PARAMETRIC CASES - RESULTS(1/2)



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BASE CASES & FORESEEN PARAMETRIC CASES - RESULTS (2/2)• Homogeneous –

isotropic globalablation behaviour

• Example for SIL base case- Radial / axial ratio ~

1.2

- Slight anisotropy due to initial radial ablation by top metal layer

- BMMT after 7.08 days (3.5 m) axial ablation ~ 2 cm/h




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• Rather homogeneous ablation and long BMMT times (4 to 9.5 days for 3.5 m)- No occurrence of a stratified configuration with a bottom metal layer

- Important conclusion regarding safety as base cases developed based on best estimate values of the different parameters + foreseen parametric cases considering plausible variations of these parameters

- To be nuanced in view of remaining uncertainties and possible parameters combinations

• Gas content in concrete is expected to play a fundamental role- Rather high H2O content (9.58 wt%) in considered SIL concrete compared to some other

studies for which a stratified configuration was observed cliff-edge effect suspected

- Strong recommendation = to study the impact of the gas content (H2O and CO2)

BASE CASES & FORESEEN PARAMETRIC CASES - CONCLUSIONS




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TABLE OF CONTENT







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ADDITIONAL PARAMETRIC CASES - DEFINITIONS

• Several additional parametric cases based on previous recommendation- Base case of SIL concrete adapted to consider a theoretical

concrete composition with varying H2O content (instead of 9.58%)

- H2O content varied between 4 and 10 wt%

- Other species normalized over the remaining fraction

- Very low CO2 content in theoretical concrete considered (< 1%)

- Global composition is theoretical and may not be representativeof an actual reactor case

• All other parameters identical to the base case for the SIL concrete

Theoretical concrete

composition

Example: Mod. SIL

5%

Al203 2.795%

CaO 10.473%

CO2 0.850%

H2O 5.000%

SiO2 80.882%




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ADDITIONAL PARAMETRIC CASES - RESULTS (1/3)

• Cliff-edge effect between 5.5 and 7.0 wt% of H2O

• 2 driving phenomena- Impact on the gas

superficial velocity

- Impact on the metal inventory

• Remark- Stratification stabilized

as opposite evolution precluded in calculation



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• Short term example with 5 wt% of H2O content

- Predominant axial ablation

- Faster MCCI kinetics leading toBMMT after only 20.5 h

- Explanation of fast axial ablationto be found in the geometrical effectlinked to the very thin metal layerthickness• Contact with cavity walls for a short

duration

• Continuous contact with basemat

• Axial ablation kinetics- Stratified 3.5 m in 20.5 h

~ 17 cm / hERMSAR 2012, Cologne March 21 – 23, 2012



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• Medium term example with 6.5 wt% of H2O content

- Predominant axial ablation stoppedat around 0.8 days configuration switch after ~ 2 m of ablation

- Rest of ablation is “homogeneous” BMMT retarded until 3.09 days

• Axial ablation kinetics- Stratified 2 m in 0.8 days

~ 10.4 cm / h

- Homogeneous 1.5 m in 2.29 days ~ 2.75 cm / h




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TABLE OF CONTENT







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CONCLUSIONS AND RECOMMENDATIONS

• Two main conclusions- Rather homogeneous ablation without any stratification for all the best estimate cases

foreseen more favourable from a safety point of view as longer BMMT times

- Fundamental role of the concrete gas content on the occurrence of a stratified configuration additional parametric cases with theoretical concretes having lower H2O contents evidence of a cliff-edge effect regarding the BMMT time

• One main recommendation- Study further the impact of the concrete gas content in future work (H2O and CO2).

• First step has been performed regarding the cliff-edge effect linked to the H2O content

• Including increasing our knowledge of concrete gas content in actual power plants


22 03 12


Session 4 “Ex-vessel corium behaviour” – Paper 4.4

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