1. France, Aix-en-Provence
Nuclear Safety Institute IBRAE Russian Academy of Sciences
MASCA MAJOR FINDINGS AND THEIR IMPLICATION ON ACCIDENT PROGRESSION SCENARIO
Presented by
V.Strizhov
MASCA Seminar
France, Aix-en-Provence
June , 2004

2. Ingot views after tests
Corium C-22
Carbon content – 0.3 wt.%
Small amount of carbon caused stratification of the melt
PRG-2 June 8 - 9, 2004
For MASCA Use only

3. Ternary phase diagram
Experiments conducted with the mixtures of U-Zr-O oxidized above 10% did not reveal stratification
Experiments showed that corium behaviour between solidus and liquidus temperatures is of great importance
Formation of liquids phases based on the zirconium (Zr0.97U0.03)O0.25
Solid matrix (U0.75Zr0.25)O1.8
PRG-2 June 8 - 9, 2004
For MASCA Use only

4. Kinetics of layers formation Steady state distribution
Focus of studies
Kinetics of layers formation
Steady state distribution
U/Zr ratio between upper and lower parts of the ingot
Carbon concentration
Post test examination results
Light and gray phases
Relation between phases
PRG-2 June 8 - 9, 2004
For MASCA Use only

5. Kinetics of layers’ formation
PRG-2 June 8 - 9, 2004
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6. Steady state distribution
PRG-2 June 8 - 9, 2004
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7. Major findings
Kinetics of layers’ formation for C-32 corium containing 0.3 wt% showed that the time for the scale of STFM facility is about 30 minutes;
Two distinct layers were found
Upper layer contains ~2 times more zirconium than the middle layer, carbon content increased up to 1.5 wt%.
middle layer enriched with uranium with low carbon content of up to 0.1 wt%.
Results were consistent with AW tests and allowed complete understanding of observed phenomena
PRG-2 June 8 - 9, 2004
For MASCA Use only

8. Interactions of corium with steel (iron)
Small scale tests
Steel was added in a solid state
Two layers were formed during the tests
Large scale RCW test
Liquid steel was added after the corium melt was formed
Complex configuration of layers was found
PRG-2 June 8 - 9, 2004
For MASCA Use only

9. Iron concentration in oxide phase
PRG-2 June 8 - 9, 2004
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10. Section of phase diagram
U/Zr=1.1 – 1.2
C32 initial corium
PRG-2 June 8 - 9, 2004
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11. Peculiarities of steel behavior in the RCW test
Steel charge;
ZrO2 case for the steel charge;
Upper tungsten heater;
ZrO2 thermal insulation;
Lattice of copper tubes of the upper cold crucible;
Upper inductor;
ZrO2 heat shield;
Thermal insulation (ZrO2 powder);
ZrO2 protective bush;
Magnetic cores;
Start-up tungsten heater;
Thermal insulation (UO2 and С-100 corium powder);
Lattice of copper tubes of the lower cold crucible;
Lower inductor;
C-32 corium loading;
Loading of FP simulants;
Pyrometric tube;
C-32 corium groats;
ZrO2 dome
PRG-2 June 8 - 9, 2004
For MASCA Use only

12. The Material Balance of the RCW experiment
PRG-2 June 8 - 9, 2004
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13. The Central Cut of the Ingot
The corium lower non-melted briquettes;
The lower metallic part;
Zone of a partially melted corium;
Roundish metallic parts in the central zone;
The ingot oxidic part;
Epoxy;
The upper metallic part;
The ingot surface;
PRG-2 June 8 - 9, 2004
For MASCA Use only

14. Partitioning of U, Zr and Fe in Metallic Parts along the Ingot Height
PRG-2 June 8 - 9, 2004
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15. Peculiarities of RCW test
Initially only part of steel interacted with corium
Mass of steel interacted about 1.02 kg
Mass of corium 50.3 kg
Steel to corium mass ratio 0.02 (similar to STFM tests with addition of about 5 g of steel)
Remaining steel interacted with the corium of about 50% of zirconium oxidation
Transient character of interactions
PRG-2 June 8 - 9, 2004
For MASCA Use only

16. Comparison of small scale tests data and RCW test data
C-32 Data
C-70 Data
PRG-2 June 8 - 9, 2004
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17. Some conclusions
Steady state characteristics of corium steel interactions were studies in a series of small and medium tests (STFM and MA series up to 20% of steel content in corium)
RCW test indicated that transient condition may play an important role during relocation of molten steel
Steel addition methods (solid/liquid)
Role of diffusion
Jet fragmentation
PRG-2 June 8 - 9, 2004
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18. Partitioning of FP simulants
Small scale tests
Influence of metal phase composition
Influence of Temperature and corium composition
Dependence upon U to Zr ratio
Peculiarities of FP Partitioning in the RCW test
Large scale RCW test
Distribution of FP in oxide phase
Distribution of FP in metal phase
PRG-2 June 8 - 9, 2004
For MASCA Use only

19. Influence of temperature and corium composition
Partitioning coefficient for metal FP such as Mo and Ru decreases with temperature increase
Partitioning coefficients Sr, Ba, Ce and La increases
Number of tests was too small to make definite conclusion
PRG-2 June 8 - 9, 2004
For MASCA Use only

20. Partitioning coefficient of Mo and Ru
Final corium oxidation degree of 65%
Final corium oxidation degree of 85%
PRG-2 June 8 - 9, 2004
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21. Partitioning coefficient of Sr and Ba
Final corium oxidation degree of 65%
Final corium oxidation degree of 85%
PRG-2 June 8 - 9, 2004
For MASCA Use only

22. Results of FP analysis for RCW test
La and Ce
Sr and Ba
Distribution of FP was not uniform through the ingot
Change of corium composition
Non uniform temperature distribution
PRG-2 June 8 - 9, 2004
For MASCA Use only

23. Peculiarities of FP Partitioning in the RCW test
Partitioning coefficient (2500 – 2600K)
Ru, Mo: 15 – 25
Sr, Ba: – 0.15
Ce, La: – 0.15
PRG-2 June 8 - 9, 2004
For MASCA Use only

24. Implications of MASCA to VVER accident progression scenarios
Analysis of core degradation scenarios
Determine degree of zirconium oxidation
Determine masses of materials relocated to the lower head
The list of scenarios includes
Station blackout scenario
LOCAs scensrios
Parameters of coria
Zirconium oxidation degree was bound to be between 30 and 40%
Mass of corium about 95% of total mass
Mass of steel 40 – 50 tons
PRG-2 June 8 - 9, 2004
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25. Structure of VVER-1000 lower head
Assembly support
Pressure vessel
Supporting plate
Perforated bottom
PRG-2 June 8 - 9, 2004
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26. Phenomena in the lower head
Debris bed
Melting and relocation of low temperature components (assemblies support)
Filling of pores with molten steel
Melting of corium
Formation of layered structure
Molten pool
Steady state conditions (Applicable for IVR case)
Transient condition
PRG-2 June 8 - 9, 2004
For MASCA Use only

27. Summary
Experiments with the molten steel and corium revealed important peculiarities of interactions
Extraction of uranium from suboxidized corium
Different layer’s configuration
Transient conditions may play a role (formation of three layers)
Debris experiments indicated that molten steel spreads through the porous debris if superheating above the melting point is sufficient (about 200 K)
Partitioning of fission products revealed that metallic FPs are concentrated in the metal phase while oxidic FP concentrated in the oxide phase. The partitioning likely depends upon temperature, the effect is not significant for reactor application.
PRG-2 June 8 - 9, 2004
For MASCA Use only