Post on 18-Jan-2016
CHOOSE EXPERTS, FIND
PARTNERS
Parametrical study on MCCI reactor cases under dry cavity conditions forassessment of parameters of importancePhilippe Dejardin
ERMSAR 2012, Cologne March 21 – 23, 2012
2
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
ERMSAR 2012, Cologne March 21 – 23, 2012
3
TABLE OF CONTENT
• Objectives and methodology
• Cases definitions, results and findings- Base cases & foreseen parametric cases
- Additional parametric cases
• Conclusions and recommendations
ERMSAR 2012, Cologne March 21 – 23, 2012
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
4
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
ERMSAR 2012, Cologne March 21 – 23, 2012
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
5
TABLE OF CONTENT
• Objectives and methodology
• Cases definitions, results and findings- Base cases & foreseen parametric cases
- Additional parametric cases
• Conclusions and recommendations
ERMSAR 2012, Cologne March 21 – 23, 2012
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
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
6
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
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
7
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
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
8
BASE CASES & FORESEEN PARAMETRIC CASES - RESULTS(1/2)
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
9
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
ERMSAR 2012, Cologne March 21 – 23, 2012
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
10
• 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
ERMSAR 2012, Cologne March 21 – 23, 2012
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
11
TABLE OF CONTENT
• Objectives and methodology
• Cases definitions, results and findings- Base cases & foreseen parametric cases
- Additional parametric cases
• Conclusions and recommendations
ERMSAR 2012, Cologne March 21 – 23, 2012
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
12
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%
ERMSAR 2012, Cologne March 21 – 23, 2012
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
13
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
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
14
ADDITIONAL PARAMETRIC CASES - RESULTS (2/3)
• 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
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
15
ADDITIONAL PARAMETRIC CASES - RESULTS (3/3)
• 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
ERMSAR 2012, Cologne March 21 – 23, 2012
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
16
TABLE OF CONTENT
• Objectives and methodology
• Cases definitions, results and findings- Base cases & foreseen parametric cases
- Additional parametric cases
• Conclusions and recommendations
ERMSAR 2012, Cologne March 21 – 23, 2012
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
17
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
ERMSAR 2012, Cologne March 21 – 23, 2012
22 03 12
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