MASCA MAJOR FINDINGS AND THEIR IMPLICATION ON ACCIDENT PROGRESSION SCENARIO Presented by V.Strizhov MASCA Seminar France, Aix-en-Provence June 10 - 11,

MASCA MAJOR FINDINGS AND THEIR IMPLICATION

ON ACCIDENT PROGRESSION SCENARIO

Presented by V.Strizhov

MASCA SeminarFrance, Aix-en-Provence

June 10 - 11, 2004

Nuclear Safety Institute IBRAERussian Academy of Sciences

PRG-2 June 8 - 9, 2004 For MASCA Use only 2

Ingot views after tests

• Corium C-22• Carbon content – 0.3 wt.%

Small amount of carbon caused stratification of the melt


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


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


Kinetics of layers’ formation

0 20 40 60Tim e (m in)

0.4

0.6

0.8

1

1.2

1.4

U/Z

r

Top layerM iddle layer

1

73

2

0 20 40 60Time (min )

0

0.4

0.8

1.2

1 .6

Ca

rbo

n c

on

ce

ntr

ati

on

(m

as

s%

)

Top layerM iddle layer1

7

2

3


Steady state distribution

0 0.2 0 .4 0 .6 0 .8Initial carbon concentration (m ass% )

0.4

0 .8

1 .2

1 .6

U/Z

r a

t/a

t


6

8

11

73

2

4

9

10

0 0.2 0.4 0.6 0.8Initial carbon concentration (m ass% )

0

0.4

0.8

1.2

1.6

2

Ca

rbo

n c

on

ce

ntr

ati

on

(m

as

s%

)


4

3

25

1186 9

10


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


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


Iron concentration in oxide phase

30 40 50 60 70 80 90 100

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4 F

e c

on

cen

tra

tion

, w

t.%

Final oxidation Zr degree

~2% Fe ~5% Fe ~10% Fe


Section of phase diagram

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.00.0

0.2

0.4

0.6

0.8

1.0

FeU+Zr

O

U/Zr=1.1 – 1.2C32 initial corium


Peculiarities of steel behavior in the RCW test

1. Steel charge;2. ZrO2 case for the steel charge;3. Upper tungsten heater;4. ZrO2 thermal insulation;5. Lattice of copper tubes of the upper

cold crucible;6. Upper inductor;7. ZrO2 heat shield;8. Thermal insulation (ZrO2 powder);9. ZrO2 protective bush;10. Magnetic cores;11. Start-up tungsten heater;12. Thermal insulation (UO2 and С-100

corium powder);13. Lattice of copper tubes of the lower

cold crucible;14. Lower inductor;15. C-32 corium loading;16. Loading of FP simulants;17. Pyrometric tube;18. C-32 corium groats;19. ZrO2 dome

1

2

3

4

6

7water

water

8

9

10

11

12

13

16

14

15

5

19

1 7

18

Gri Uo2 (20 )t mm

Br bot (40 )iq mm

1 lev H1 (130mm)

2 lev H1 (220mm)

3 lev H1 (320mm)

4 lev H1 (380mm)

4 lev H2 (380mm)

5 lev H1 (470mm)


The Material Balance of the RCW experiment

The initial loading Mass (kg)

Components collected after the test Mass (kg)

The С-32 corium 66.415 The ingot mass 53.180

UO2 plates 1.480 Oxidic part 45.250

FP simulants 0.570 Including:

Metallic part 7.930

Mass of components outside the ingot 43.819 Stainless steel 12X18H10T in the upper section

4.643 Non-melted briquettes and UO2

plates 19.929

Stainless steel 0.060 Thermal insulation (50 % of С-100 corium + 50 % of uranium dioxide)

24.830 Including:

Thermal insulation (50 % of the С-100 corium + 50 % of uranium dioxide)

23.830

Total weight 97.938 Total weight 96.999

Disbalance 0.939


The Central Cut of the Ingot

1. The corium lower non-melted briquettes;

2. The lower metallic part;3. Zone of a partially melted

corium;4. Roundish metallic parts in

the central zone;5. The ingot oxidic part;6. Epoxy;7. The upper metallic part;8. The ingot surface;


Partitioning of U, Zr and Fe in Metallic Parts along the Ingot Height

0 10 20 30 40 50 60 70Concentation (mass%)

3

2

1Bottom

Middle

Top

ZrU

SS


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

40 50 60Cn

0

40

80

120

160

200

240

Hei

gh

t (m

m)

in area of largemetallic parts

10

11

7

8

1

3

2

54

13

14

15


Comparison of small scale tests data and RCW test data

0.00 0.05 0.10 0.15 0.20

10

15

20

25

30

35

40

45

50

55

60

65

Me/(Me+Ox)

Co

nce

ntr

atio

n, w

t.%

U Zr Fe(SS)

0.00 0.02 0.04 0.06 0.08 0.10 0.120

10

20

30

40

50

60

70

80

Co

nce

ntr

atio

n, m

ass

%M

st/(M

st+M

cor)

U Zr Fe(SS) U(RCW) Zr(RCW) SS(RCW)

C-32 Data C-70 Data


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


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


Influence of temperature and corium composition

Simulants of fission products Test number Mo Ru Sr Ba Ce La

Final corium oxidation Cn = 65

MA3 2500oC 82.0 58.0 0.057 0.013 0.093 0.090 FP#1 2600С 16 16 0.16 0.13 <0.05 0.42 FP#6 2600С 14.2 24 0.069 0.025 0.037 0.046 FP#3 2700С 6.1 11 0.13 0.1 <0.1 0.15

Final corium oxidation Cn = 85

MA4 2500oC 37 56 0.026 0.031 0.032 0.021 FP#7 2600С 61.7 76.2 0.13 0.1 <0.14 0.24 FP#8 2600С 50.6 73.3 0.21 0.15 0.3 0.02

• 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


Partitioning coefficient of Mo and Ru

2500 2550 2600 2650 2700

5

10

15

20

25

30

Pa

rtiti

on

ing

Temperature, oC

Mo Ru

2500 2550 260030

35

40

45

50

55

60

65

70

75

80

85

90

95

Pa

rtiti

on

ing

Temperature, oC

Mo Ru

Final corium oxidation degree of 65% Final corium oxidation degree of 85%


Partitioning coefficient of Sr and Ba

2500 2550 2600 2650 2700

0.00

0.05

0.10

0.15

0.20

Pa

rtiti

onin

g

Temperature, oC

Sr Ba

2500 2550 2600

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Pa

rtiti

on

ing

Temperature, oC

Sr Ba

Final corium oxidation degree of 65% Final corium oxidation degree of 85%


Results of FP analysis for RCW test

0.0 0.2 0.4 0.6 0.8 1.0

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

Co

nce

ntr

atio

n,

wt.

%

Elevation, rel units

La Ce

0.0 0.2 0.4 0.6 0.8 1.00.08

0.09

0.10

0.11

0.12

0.13

0.14

0.15

0.16

0.17

0.18

0.19

Co

nce

ntr

atio

n,

wt.

%

Elevation, rel.units

Sr Ba

La and Ce Sr and Ba

•Distribution of FP was not uniform through the ingot•Change of corium composition•Non uniform temperature distribution


Peculiarities of FP Partitioning in the RCW test

ko of the metallic part FP upper middle lower

Sr 0.14 0.24 0.20 Ba 0.09 0.17 0.02 La 0.26 0.33 0.19 Ce ≤0.02 ≤0.15 ≤0.15 Ru 0.55 0.61 42.90 Mo 5.36 5.00 39.29

Mass concentration of elements, % Sample Sr Ba Ru Mo La Ce

1. Upper 0.015 0.013 0.017 0.15 0.020 <0.01 2. Middle 0.026 0.025 0.019 0.14 0.026 <0.01 3. Lower 0.002 0.003 1.33 1.10 0.015 <0.01

Partitioning coefficient (2500 – 2600K)

Ru, Mo: 15 – 25Sr, Ba: 0.07 – 0.15Ce, La: 0.05 – 0.15


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


Structure of VVER-1000 lower head

Assembly support

Pressure vessel

Supporting plate

Perforated bottom


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


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.

MASCA MAJOR FINDINGS AND THEIR IMPLICATION ON ACCIDENT PROGRESSION SCENARIO Presented by V.Strizhov MASCA Seminar France, Aix-en-Provence June 10 - 11,

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