MASCA PROJECT: MAJOR ACTIVITIES AND RESULTS
V.Asmolov, D. Tsurikov
RRC “Kurchatov Institute”, Moscow, Russia

Abstract
The MASCA Project implies a program of corium tests of different scale and various prototypiccomposition experiments (with corresponding pre- and post-test analyses) to investigate the influenceof chemical composition of the corium mixture on heat transfer in a stratified molten pool (U-Zr-OFe(SS)-C(B)) and partitioning of basic corium components and FP between layers. The MASCA
Project results would provide the technical support for the assessment of the in-vessel melt pool
retention strategy as well as of the ex-vessel phenomena.
The major Project activities included:1.

Development of technology to conduct the high temperature corium tests including design,
fabrication and assembly of a large-scale facility capable to heat up and retain molten coriumand steel at relevant temperatures under controlled conditions;2.

Performance of a confirmatory large-scale test to confirm the major findings.

3.

Performance of small- and middle-scale corium experiments to investigate separate
phenomena including:• Carbon impact on the corium stratification;• Stratification in the solidus-liquidus range;• Study of corium components partitioning in the stratified metal-oxide pool;• FP partitioning between different phases;• Molten metals migration through the oxide porous matrix;• Boron behaviour and its impact on the stratification;• Measurements of material properties.
4. Performance of salt tests to study heat transfer in the stratified molten pool.
The Project major findings are presented in the paper.

11. Background
The in-vessel retention of a severe accident in the vessel of a light water reactor (LWR) by
external cooling of the vessel has been recognized as an attractive accident management measure forboth current design reactors and new plant designs based on the passive safety systems.
Since in-vessel melt retention has become an important safety objective for nuclear reactors, it isimportant to evaluate and model the relevant phenomena that will contribute to melt retention under
prototypical accident conditions. At the same time, even if not aiming at in-vessel retention, there is aclear need to understand the convective molten pool behaviour, since melt pools have important
implications on the core relocation and the RPV failure mode that both, in turn, have further
consequences on the subsequent behaviour of corium outside the vessel, which depends strongly on
the melt composition and ejection mode. Furthermore the understanding of oxide-metal behavior isalso of interest for various ex-vessel situations involving corium pools or layers of molten corematerials.
The in-vessel retention related phenomenology includes a variety of heat transfer and materialinteraction phenomena [1] such as• Heat transfer in the debris bed and ceramic melt;• Chemistry of corium components including UO2, ZrO2, Zr and components of steel which
determine possible melt stratification;• Thermal and chemical interactions of corium and its components with the reactor pressure
vessel;• Ex−vessel boiling heat transfer in case of the reactor cavity flooding;• Mechanical behaviour of the vessel under loads caused by internal pressure and thermal
stresses.
Numerous experimental studies with simulant materials, such as COPO, ACOPO, BALI,RASPLAV-SALT and SIMECO, dealt with the problem of heat flux distribution around a
volumetrically heated molten pool at wide range of Rayleigh numbers. The main focus for thesestudies has been the thermal loading imposed by the core melt on the reactor pressure vessel (RPV)
lower head.
Thermal hydraulic studies of the melt pool behaviour have also included cases where a molten
metal (steel) layer could form on top of oxidic corium due to very limited solubility of steel in theoxides (the density of steel being lower than the density of core oxides). The heat-focusing effect of
this molten metal layer was of concern, because the vessel walls adjacent to the metal layer were
subjected to increased heat fluxes, which could lead to substantial localised melting of the walls.
Experimental programs have also been conducted to investigate the critical heat flux for theboiling process initiated on the outer surface of the vessel due to cavity flooding (external vessel
cooling).
Although many experimental data with simulant fluids are available, only limited experimental
data with UO2 melt were available [2, 3]. The scale of corium experiments was too small anddistortion of the results due to different factors could be significant. There are obvious differences
between prototypic core materials and simulant fluids which were used mostly in the previous
experimental studies. These aspects may influence the applicability of the heat transfer results
obtained with simulant fluids to reactor conditions and signify a need for the confirmatory
experimental and analytical studies of prototypic corium pool behaviour under external coolingconditions. The lack of data related to the behaviour of large convective pools formed by prototypicmolten core materials were the reason for the initiations of the new project arrangements.

2

Studies of the impact of real materials have been performed in the frame of OECD RASPLAV
project. It demonstrated that the homogeneous corium melt behaved comparably to simulant materials
in natural circulation, therefore previous evaluations based on simulant material data could be scaled
to prototypic reactor conditions. It was shown that such a behavior can be expected if molten poolcontained oxidic materials.
However, two of the four large-scale RASPLAV tests conducted with suboxidized corium
exhibited an unexpected behaviour. Post-test examinations showed that the melt pool, initially of ahomogenous composition and density, stratified into two layers of unequal density. The lower layer ofa denser material was richer in uranium while the upper lighter layer was richer in metallic Zr. Those
results indicated that the behavior of the corium molten pool likely depends upon its composition andzirconium oxidation degree [4]. RASPLAV project dealt with the corium of different oxidation
degree. Another subject of interest was the concern about the behavior of steel in contact with corium.
As heat focusing effect may change significantly the distribution of heat flux, interactions between
molten corium and steel under prototypic conditions is of great importance. In light of these results theinterest was to obtain more data with respect to prototypic core materials behaviour at hightemperatures.
The MASCA Project started in July 2000 was concentrated on the detailed investigation of thechemical behaviour of corium in contact with structural materials, with emphasis mainly on steel. The
MASCA Project implies a program of corium tests of different scale and various prototypiccomposition experiments (with corresponding pre- and post-test analyses) to investigate the influenceof chemical composition of the corium mixture on heat transfer in a stratified molten pool (U-Zr-OFe(SS)-C(B)) and partitioning basic corium components and fission products (FP) between layers. The
experiments were not directly aimed at reproducing the in-vessel situation because the main goal of
MASCA project is to study material interactions rather than molten corium pools as in RASPLAV.
2. Management and Organization
The Nuclear Energy Agency of the Organisation for Economic Co-operation and Development(NEA-OECD) has, since 2000, sponsored a collaborative project on Severe Accidents carried out in
Russia. This project, entitled the MASCA(MAterial SCAling) Project, had the basic objective toprovide data on the behaviour of molten core materials chemical interactions under severe accident
conditions.
Agreement on the OECD MASCA Project was prepared and signed by the OECD member-states
and Russia in July 2000. Signatories to the project included Belgium, Canada, Czech Republic,
Finland, France, Germany, Hungary, Republic of Korea, Italy, Japan, the Netherlands, Spain, Sweden,
Switzerland, the United Kingdom, and the United States.
The studies in the frame of the Project have been carried out by the Russian Research Centre
Kurchatov Institute (RRC KI, Moscow) in co-operation with a number of scientific and research &production associations of Russia: A.P. Alexandrov Research Institute of Technology (NITI, SosnovyBor), Luch Scientific Production Association (Podolsk), Nuclear Safety Institute (IBRAE) Russian
Academy of Sciences (Moscow).
The management and organisation of the MASCA Project is practically the same as RASPLAV
Project one. Overall control and direction of the project was vested in the Management Board (MB)that consisted of one member designated by each of the signatories. The primary function of the MB
was to approve the overall and the annual project workscope and budget. The Program Review Group(PRG) was formed from members designated by each signatory. The primary function of the PRG was
to be the technical advisor to the MB for project activities. The Program Review Group also provided
technical advice and recommendations for the Operating Agent (OA), who was responsible for3

implementing the project objectives in accordance with the project agreement and directions from theManagement Board.
3. MASCA Project Operations
The major goals of the MASCA Project are the following:• Investigation of the influence of chemical behaviour on heat transfer in stratified molten
pools (U-Zr-O-Fe(SS)-C(B));• Investigation of fission products (FP) behaviour in a molten pool and in particular• Partitioning of FP between layers in case of stratification;• Partitioning of FP between phases during melting and solidification;• Distribution of FP simulants in the melts;• Expansion of material properties data base;• Development of computer models describing relevant phenomena.
The Project goals have been achieved through corium tests of different scale, including pre- andpost-test analyses and development of computational models, additional measurements of thermophysical properties of the melts such as density, thermal conductivity and liquidus-solidus
temperatures. Separate effects were studied in series of small-scale and midle-scale experiments, anintegral test of the AW-200 type was performed to confirm major findings. The key MASCA Project
items and corresponding facilities are presented in Figure 1.
Figure 1. Major MASCA Project Activities

Melt
objective stratification
mechanism

facilities

SALT
TESTS

CORIUM TESTS

Item

STFM1
STFM2

Boron
Coriumbehaviourinteraction
and itswithimpact on
steelstratification(iron)

STFMB

MigrationofmoltenLarge-scale
FP
Material
metal
confirmatory
partitioning throughproperties
test
porousoxide
debrisSTFM
STFM
KORPUSRASPLAV-2 RASPLAV-2
TULPAN
RCW
RCW

RCW

TIGEL

Heat
transferinstratified
moltenpool

RASPLAVA-SALT-2

Thus the major MASCA Project activities included:1.

Development of technology to conduct the high temperature corium tests including design,
fabrication and assembly of a large-scale facility capable to heat up and retain molten coriumand steel at relevant temperatures under controlled conditions;2.

Performance of a confirmatory large-scale test to confirm the major findings.
4

3.
•
•
•
•
•
•
•

Performance of small- and middle-scale corium experiments to investigate separate
phenomena including:
Carbon impact on the corium stratification;
Stratification in the solidus-liquidus range;
Study of corium components partitioning in the stratified metal-oxide pool;
FP partitioning between different phases;
Molten metals migration through the oxide porous matrix;
Boron behaviour and its impact on the stratification;
Measurements of material properties.

4. Performance of salt tests to study heat transfer in the stratified molten pool.
In the corium experiments in MASCA Project the corium of the different compositions was used.
These corium compositions are presented in Table 1.
Table 1. Corium Compositions Studies in the MASCA Project
Coriumcomposition

Composition (mol. %/wt. %)Zirconiumoxidation (%)

U/Zr
ratio

UO2

ZrO2

Zr

C-22

22

62/81.8

8.4/5.0

29.6/13.2

1.6

C-32
C-50

32

54.5/76.2

14.5/9.3

31.0/14.5

1.2

50

62/80.4

19/11.3

19/8.3

1.6

C-75

75

56.4/75.2

33.2/20.2

10.4/4.6

1.3

C-100

100

62/78.1

38/21.9-

1.6

3.1 Carbon impact on the corium stratification
To study the stratification phenomenon in the frame of MASCA project a special attention was
paid to the possibilities of melt stratification and separation. Two mechanisms were considered:• Stratification induced by small amounts of impurities (carbon);• Separation of components in the solidus – liquidus temperature interval.
A series of 11 small-scale experiments were made to quantify the effect of corium stratification
due to small additives of carbon. The experiments were performed at the STFM test facility in a hottungsten crucible with dimensions ∅ 14 × 0.5 mm in diameter and 70 mm high. The boundary
conditions along the crucible height during experiments were isothermal within the same limits. In all
experiments the maximum exposure temperature was T = 2550oC. Heating up rate was fast and slow:
500 – 600o/min or 8o/min correspondingly. Cooling down rate was about 50o/min. All experiments
except of those which studied stratification kinetics exposure time was 60 min. For studying kinetic
effects the exposure time varied in the range 5, 15 and 60 min.
Experiments were conducted using C-32 corium and carbon content in the corium varied between
0.006 to 0.69 wt%. Stratification kinetics of the corium containing 0.3 – 0.36 wt% of carbon wasstudied in 4 experiments – STFM1(1, 2, 3, 7). The amount of carbon is approximately corresponded to
the RASPLAV-AW-1 test. Results of the experiments showed that carbon content in the upper layer
increases gradually and decreases simultaneously in the bulk corium. U/Zr ratio exhibits similar
behavior. The kinetics is fast enough, after first 15 minutes the process slows down significantly. It is
important to note that no impact of the heating rate (8oC/min and 500oC/min) onto the process ofcarbon redistribution was revealed.
5The experiments with the exposure time of 60 minutes were used to analyze the final state as afunction of initial carbon content which varied in the range between 0.085 wt% and 0.69 wt%. Resultsof experiments showed that if carbon content in the initial corium was less than 0.2 wt%, carbon
redistribution and change of U/Zr ratio in the corium along the ingot height melt was insignificant.
However if carbon concentration in the initial corium exceeded 0.2 wt% significant redistribution of
corium components and change of U/Zr ratio along the ingot height was observed: increase of carbon
and zirconium concentrations in the top layer and decrease in the middle layer. This was accompaniedby the growth of the zirconium based phase in the upper layer.
Two experiments – STFM1/5 and 6 were performed in the argon environment with addition of
CO gas (0.1 vol.%) to study the process of corium carbidization from the gas atmosphere. No
noticeable increase of the carbon content in the top layer was observed in C – 32 corium containing
0.36 wt% of carbon in comparison with the similar experiment #2 without CO gas addition. Some
increase of the carbon content in the top layer (up to 0.1 wt%) and in the bulk corium volume (up to
0.06 wt%) took place in the test #6 with low initial carbon content (0.006-0.009 wt%). This increase ofcarbon content was found to be insignificant and did not lead to corium stratification into two layers.
3.2 Stratification in the solidus-liquidus range
Six small tests (~ 0.5 kg) were conducted to study possibility of C - 32 corium stratification in thetemperature range of TSol – TLiq into the top liquid layer based on Zr(O)x and the bottom solid layer
based on (UZr)O2-x and to study the stability of corium configuration if such kind of stratification takes
place. These experiments were conducted using the same STFM facility. Briquettes and powder of
C-32 corium (U/Zr = 1.2 at./at., carbon content 0.006 – 0.009 wt%) were fabricated by pressing of thepowder mixture (UO2, ZrO2, ZrH2) in accordance with the technique developed for
RASPLAV-AW-200-4 experiment.
In STFM2/1-5 experiments tungsten crucibles were loaded with corium particles (1 – 4 mm),porosity of the loading was 30-50%. Heating up in all of the experiments was performed with the rateof 500-600oC/min at the T > TSol. Cooldown rate to TSol was 50oC/min.
The main results are the follows. For isothermal tests there was no onset of stratification attemperature 2150oC and 2300oC. For the test STFM#2/3 conducted at the temperature of 2200oC post
test examination exhibited increase of the light phase Zr(O)x concentration and corresponding decreaseof U/Zr ratio in the top layer. Enrichment of the top liquid layer with zirconium has occurred
simultaneously. Concentration of the light phase has decreased and the fraction of the grey phase
based on UZrO2-x has increased in the bottom solid layer. The ratio of the light and grey phases
fraction in the ingot top and middle parts reached the value of 3.5.
The compositions of phases found during the post test examination are shown in the Table 1. The
light phase mainly consists of zirconium Zr(O)x phase with small amount of uranium while grey phasepresents oxide phase (UZr)O2-x.
Table 2. Phase Compositions
Phase

Concentration (wt%)

Phase molecular formula

U

Zr

O

Light

9.21

85.19

4.79

(Zr0.96U0.04)O0.30

Gray

74.29

12.10

13.70

(U0.70Zr0.30)O1.93

Experiment #6 when corium was heated first to 2500oC and then cooled down to 2200oC andexposed for 60 minutes did not indicate significant differences in light phase composition in the top
6and middle layers were insignificant, coefficient of the light and grey phase fractions ratio in the layers
was 1.7, which is 2 times less than in the #3 experiment. Similar results were observed for the casewhen corium was exposed first at the temperature of 2200oC and then heated up to 2600oC. The
structure of the ingot was found to be rather uniform.
3.3 Study of Corium Components Partitioning in the Stratified Metal-Oxide Pool
The study of the interactions between corium and metals is an important part of the interactions incourse of accident. Due to significant melting temperature difference such an interaction can be
expected when corium is solid or liquid. Special test series involving different experimental facilities
and different experimental conditions has been performed to study the interactions between coriumand steel in liquid phase.
The objective of this experimental series was to obtain quantitative and qualitative characteristics
of uranium, zirconium and steel components partitioning between different phases. The following
facilities were used:• Small scale STFM facility with the loaded mass about 0.5 kg;• Middle scale RASPLAV-2 facility with the loaded mass of about 2 kg;• Large scale RCW facility with the loaded mass about 100 kg.
All these facilities were completely upgraded and modernized to conduct the tests with coriumand steel. The facilities rest on using inductive heating and cold crucible technique, which allowed
maintaining integrity of the facilities. The detailed descriptions of these facilities are presented in thereports.
In the experiments the following parameters varied: corium composition (variation of oxidation
degree and uranium to zirconium ratio), metal composition (experiments with the iron and stainlesssteel). A total of 16 small, 4 middle and 1 large- scale test were conducted.
For each test, the temperature was raised above the liquidus temperature of corium. The exposure
time for small-scale tests varies between 10 to 60 minutes. The chemical equilibrium was found to bereached because of the small scale of the samples and the stirring due to induction forces. Typical
exposure time for medium scale tests was 30 minutes. The metal and oxide samples were carefully
examined after the tests.
The large-scale test was conducted with the aim to study scaling effects and confirm the findingsof small and medium scale tests. Pretest analyses were performed to assess the power input scenario,
melt progression scenario and temperatures during test performance. For the conduction of RCW test
the same approach of cold crucible technology was used. The facility consists of two sections eachheated separately by its own inductor as it is shown in Figure 2. The facility consists of two sections
located vertically one above the other and integrated into one assembly. Each of the melting
compartments is located inside the bearing supporting cylindrical lattice made from water-cooled
copper tubes and copper headers for water input-output that form a cold crucible.
The corium briquettes and FP simulants were heated and melted in the lower section. After that,steel preform was melted in the upper section, and steel runs down through the discharge channel onto
the corium melt in the lower section where they interact. Power necessary for heating and melting ofloadings in each section is supplied from the self-contained inductors through the clearances among
pipes of the cold crucibles. The depth of the melting compartment in the lower section is 700 mm, theinner diameter is 176 mm. The lower section loading consisted of 26 layers of the C-32 corium ringbriquettes and of the loading of FP simulants. The corium briquettes were put on the powder thermal
insulation 40 mm thick (the mixture of UO2 and the C-100 corium powders). The loading of FP

7simulants was located in the loading middle part between the levels of 146 и 342 mm from the section
bottom.
Figure 2. The RCW Facility Schematics
17

1
2
3

1. Steel charge;

4

2. ZrO2 case for the steel charge;

5

3. Upper tungsten heater;

6

4. ZrO2 thermal insulation;
5. Lattice of copper tubes of the upper cold
crucible;
6. Upper inductor;

water

7

7. ZrO2 heat shield;

8

8. Thermal insulation (ZrO2 powder);1999. ZrO2 protective bush;10. Magnetic cores;
11. Start-up tungsten heater;

10

12. Thermal insulation (UO2 and С-100 corium
powder);11

13. Copper tubes of the lower cold crucible;

18

14. Lower inductor;

1215. C-32 corium loading;16

16. Loading of FP simulants;

13

17. Pyrometric tube;

14

water

15

18. C-32 corium groats;
19. ZrO2 dome

A layer eight millimeters thick of the powder thermal insulation (the mixture of UO2 and the
C-100 corium powders) was filled between the loading and the cold crucible pipes. The same mixture
filled up all clearances between the cold crucible pipes and inductor.
Thermal shields made of ZrO2 ceramics (the bushing, dome, shield on the pyrotube) were locatedin the upper zone of the melting compartment (above the melt surface level) to reduce thermal losses
upwards and to the walls. The dome was also covered with ZrO2 powder.
A pipe of the start-up tungsten heater 65 mm long located along the compartment axis was put
into the loading down to the depth ~ 100 mm. Tungsten heater was heated by the inductor field withthe frequency 8 – 10 kHz up to the temperature 2500 – 2600 °С. It heats, in its turn, the surrounding8briquettes by the radiationally-conductively up to the formation of electrically closed rings and theoccurrence of the necessary electric conductivity in those (at f = 10 kHz, Tinitial heat generation ≈ 1500 °С).
A melting compartment of the upper section is formed by a tungsten pipe-heater insulated fromthe cold crucible pipes by the layers of Al2O3 coating (the layer is 10 mm thick) and of ZrO2 powder(the layer is 14 mm thick). The compartment is supported by heat-insulating rings made from ZrO2
ceramics.
Inside the compartment, a stainless steel charge (a pipe ~ 9 mm thick) is placed into the casemade of ZrO2 ceramics. The case prevents the contact of melting steel with the heater tungsten.
The power input scenario was estimated in a series of the pre-test calculations before the test inorder to assess the characteristic power input and time table of events, which allowed to follow theheating and melting processes. The test was conducted in several phases, namely:
1.

Heat up at the moderate level of power up to the target tungsten temperature of about
2200oC;

2.

Removal of the starter heater from the crucible after the melt front reached cold walls;

3.

Sustained heating of corium at the appropriate power level to provide the corium heating andmelting;

4.

Heating of steel in the upper section and pouring of that into the melted corium;

5. Quasi-steady state operation.
The starter tungsten heater was removed after the beginning of the radial melting. The sustained
heating of the corium loading provided downward motion of the melting front. The thermocouples
located in the peripheral area indicated rapid temperature increase. As the heating efficiency increased
gradually, the input power was reduced during the third phase to maintain approximately constantmelting front velocity.
Post-test examination confirmed most of the results already obtained in smaller scale tests.
However, some differences in the final stratification and distribution of phases appeared. The main
distinction of the RCW test from the series of tests STF and MA lies in the scale factor. The mass
values of the corium and steel interacted in the RCW tests are 20 - 30 times higher than those in the
МА-1, 3 tests and ~ 150 times higher than those in the tests of the STF series.
Analysis of the obtained results demonstrated that the scale factor influences the interaction
kinetics. In the tests with low masses (~ 300 g of corium), the interaction process is completed withinτ ≤ 15 min, and the metallic part absorbed uranium up to the concentration 50 mass % relocates onto
the pool bottom. In the МА-1 test with the corium mass ~ 1500 g, during the interaction timeτ ≤ 30 min the metallic part that absorbed uranium up to the concentration ~38 mass% relocates onto
the pool bottom. In the RCW test with the molten corium mass ~ 45250 g, the lower part seems to besaturated with the uranium up to the concentration 40 – 50 mass %. Total mass of uranium migrated
into steel was 3.1 kg. An additional absorption of ~ 2.2 kg of uranium is necessary to achieve uranium
concentration ~ 50 mass % in all metallic parts. It is necessary to note that the method of steel
introduction into the melt (in the solid or liquid forms, in one part or several parts) as well as the ratioof steel mass to the surface of the contact with the corium may also influence the kinetics of thecorium interaction with metal.
In RCW test the scale factor allowing to observe different stages of steel fragmentation, saturationof that with uranium and zirconium and relocation of fragments onto the liquid pool bottom is thepeculiar feature of the RCW test in comparison with the tests STF and МА.

93.4 FP Partitioning between Different Phases
Experiments with the corium and steel performed in the frames of MASCA Project showedsignificant redistribution of major corium components such as uranium and zirconium between
metallic and oxide phases. Significant part of uranium, zirconium and oxygen pass into the steel melt
due to the interaction of structural steel with a suboxidised corium. The FP series of tests was aimed at
the investigations of mechanisms associated with the partitioning of low-volatile fission products
between stratified melts of the metallic and oxidic phases. Mo, Ru, Sr, Ba, Ce and La were chosen as
the simulants of fission products.
Three experimental facilities were used for study of FP behavior, large scale RCW facility, two
middle scale tests MA-3 and MA-4, and a series of small scale experiments performed at the STFM
facility. In the tests several parameters such as zirconium oxidation degree, ratio of iron (steel)introduced in the corium and U/Zr atomic ratio.
Initial loading of different components for different experiments are shown in Table 3. As FPs
were added in a different chemical forms in the brackets the recalculated amount for the pure species
are shown. Material balances made up for each test allowed to demonstrate that the average
concentration for each FP in the STFMFe test series was 0.4 ± 0.03 mass %. For MA tests it wasslightly higher about 0.53 mass % for each FP simulant.
Table 3. Initial Loading of FP Simulants (grams)
Facility

SrO

BaO

La2O3

CeO2

Mo

Ru

STFM-FP
MA-3
MA-4
RCW

1.15 (0.97)
10.64 (9.0)
9.46 (8.0)
135 (80)

1.15 (1.02)
10.05 (9.0)
8.93 (8.0)
89 (72.4)

1.15 (0.98)
10.55 (9.0)
9.38 (8.0)
94 (80)1.15 (0.94)
11.06 (9.0)
9.83 (8.0)
98 (80)

1.15
9.0
8.0
80

1.15
9.0
8.0
71

In the STFMFP series to ensure the uniform FP loading, a part of sintered coria was grinded
under nonoxidizing conditions down to the groats of ~ 500 µm typical size into which chosen elements
were added in the form of a powder mixture of Mo, Ru, BaO2, CeO2, SrCO3, La2O3 in the quantity of
0.4 mass % scaling to metals. Powder mixtures of corium with FP stirred uniformly were loaded into
tungsten crucibles of 30 mm inner diameter and ~ 130 mm height. The experiments were conducted in
the argon atmosphere in the following mode: fast heating to the temperature of complete melting
2400 – 2600° depending on the corium oxidation degree, 1 – 3 minute exposition and the inductor
switching off.
U, Zr, Zrfree, Fe were determined by the standard chemical methods. Fission products simulants
were determined by the plasma emission-spectrum method. The method sensitivity is as follows:
Mo - 0.001; Ru - 0.002; Ba and Sr - 0.0002; Ce - 0.01; and La - 0.001 mass %. The relative error is≤ 10 %. Simultaneously, the x-ray structural phase analysis was performed.
The analysis of fission products in the corium and the ingot metallic parts was performed by theplasma emission-spectrum method.
The following parameters varied in the STFMFP tests:• The zirconium oxidation degree. Initial oxidation degree of the corium mixture before thetest was about 45% for tests #1, #2, #3, #6, and about 70 for tests #7 and #8. Final oxidation
degree was about 65% for tests #1 through #6, and 80 – 85% for tests #7 and #8.
• One tests #6 was performed with the stainless steel.
• Temperature in the tests varied between 2600oC and 2700 oC.

10•

One test was conducted with the U/Zr ratio equal to 1.6 (FP#2), in all other experiments theratio was 1.2.

Two MA experiments were conducted at lower temperature about 2500oC and amount of steel
added to the corium was higher about 0.1 and 0.2.
The following parameters were chosen as main parameters, which determine the partitioning of
FP between phases: temperature, final corium oxidation degree, and U/Zr ratio. Moreover the
dependence upon steel (iron) to corium ratio was analyzed. Partitioning coefficient was calculated asratio of concentrations between metal and oxide phases.
Results of the studies on partitioning of fission products (Mo, Ru, Cr, Ba, La, Ce) in the oxideand metallic melt phases confirmed that metal simulants such as Mo and Ru are concentrated in themetal phase, while oxide component Sr, Ba, Ce, and La are distributed in the oxide corium.
3.5 Molten Metals Migration Through the Oxide Porous Matrix
A series of 10 small (~ 0.5 kg) and 1 medium scale (~ 7 kg) tests were dedicated to the study ofmolten metal migration through a porous corium debris bed.
Coria of different compositions namely C-32, C-70, C-100 compositions with the atomic ratio of
U/Zr = 1.2 were employed in the tests. Most part of experiments was conducted with the corium
particles loading with the sizes of particles 1.2 - 3.5 mm, and one test (the K-1 test) was with thecorium fragments of ~ 8 × 8 × 10 mm size.
The molten metals were presented by the steel of the St30 quality, stainless steel 12X18H10T,
and by the alloy of stainless steel (85 mass %) and zirconium (15 mass %)The corium fragments and particles were produced by cutting or crushing of the corium sinteredbriquettes (the C-32 corium was sintered under the temperature 1700°C, the C-70 and C-100 coria
were sintered under the temperature 2000°C). The particle fractions were prepared by the alteringbolting through the riddle with openings of 1.2 and 3.5 mm. illustrates the size distribution of thecorium particles.
One test was made with 1cm debris to show the effects of surface tension and wettability. The
metal consisted of either steel or a alloy of Zr and steel. The temperature was deliberately chosen in a
relatively low range (between 1900K and 2300K) above the melting temperature of the metallic alloy,
however lower than the corium melting temperature. In some cases, the melt progression through theparticle bed was observed whereas in other cases there was no metal penetration. Chemicalinteractions between the solid particles and the liquid metal were observed and samples were analyzed
to measure compositions.
Most tests were performed in the KORPUS facility in the argon atmosphere [5]. The heating
device consisted of a resistive graphite heater of a cylindrical geometry and up to 20 kW power. A
tantalum cup in which studied test assemblies were placed was located in the heater. As a rule, one test
assembly was placed into the heating device in each test. In one case three test assemblies, K-7, K-8,
and K-9, were tested simultaneously in one heating device. Test conditions for these assemblies were
the same ones. Energy to heat a test assembly was transferred by the radiation from the graphite heater
to the tantalum cup and from the Ta cup to the test assembly. As K test series was conducted in a
carbon heater three supporting tests were conducted to study the possible carbon influence on the test
results.
The T-8 test was performed in the TULPAN facility [5] to study the interaction of the C-32
corium particles with stainless steel in non isothermal conditions and in a larger scale. One of the goals
was to determine the depth to which molten steel may penetrate through the porous debris. The goals
11for the post-test examination was also to study interactions occurred during penetration. The TULPAN
facility represents a gas-vacuum induction furnace with a graphite heater. The inductor power at thefrequency 1000 Hz is up to 250 kW. The temperature gradient was maintained by the radiation fromthe outer surface of the test unit. TULPAN T-8 test conducted in the vertical temperature gradientindicated that the penetration of steel was observed up to the temperature about its melting point.
Results of experiments demonstrated several mechanisms for the penetration of molten metal in
the porous debris:
1.

Filling of the open porosity among particles by liquid metal. This process depends upon thedebris particle size, the wettability of the corium particles and surface tension which are inturn depend upon composition and temperature;2.

The interactions between molten metals and corium particles near the contact area between
phases. The depth of such penetration did not exceed ~ 3.2 mm.

3.

In some cases (under the temperature higher than 1800°C) the metal migration by themechanism “vaporization-condensation” on the surface of particles located deeply in theloading was found

3.6 Boron Behaviour and Its Impact on the Stratification
In case of a severe accident control rods fabricated with a use of boron carbide may be one of thebasic boron sources for the corium melt in the reactor vessel. A total mass of B4C, as it follows fromthe reference [6], may range for different reactor types from 270 kg (VVER-1000) up to 900 kg(BWR). This corresponds to 0.25 and 0.5 mass% of the core mass for each case. Earlier [7], on
studying carbon impact on the behaviour of the suboxidized C-32 corium, it was shown that themelting and further freezing resulted in the stratification of that into two layers at the concentration ofcarbon in the initial corium higher than 0.2 mass%.
Therefore, the existence of similar stratification phenomena in the corium may be also expectedin the presence of boron. On studying the impact of boron carbide, it is of an additional interest to
determine the opportunity for carbon and boron combined impact on the stratification processes in thesuboxidized corium as well as the partitioning of boron and carbon between the oxide and metallic
melt phases of the core.
Three small scale experiments have been conducted with the corium containing the boron carbide
in the STFM facility [8]. The first experiment have been performed in a tungsten crucible and was
similar to the experimental series with the carbon, all other experiments have been performed in a cold
crucible like the series with the corium and iron.
Corium was made from the initial components, namely: uranium oxide (UO2), zirconium oxide(ZrO2), zirconium hydride (ZrH2), and boron carbide (B4C). The initial materials in the form of
powders were thoroughly blended, pressed and sintered in the furnaces with metal heaters in theatmosphere of purified argon in protective casks made of tantalum. Then discs of corium were sinteredat the temperature about 1900 °C during 1 hour. Discs containing additionally 0.5 mass% of boron
carbide were sintered under the temperature ~ 2150 °C during 15 minutes. The actual content of basic
elements and carbon were analysed in the produced corium compositions.
Metal Fe was employed in the test studying boron partitioning between oxidic and metallic
phases. The presence of impurities Mn - 0.21, Si - 0.15, and C - 0.05 mass% were found in thecomposition of iron. The scenario for two experiments included heating up to the temperature 2550°C
within 20 minutes, exposure during 30 minutes and cooling down to 1800°C within 15 minutes. Post
test examination included chemical and phase composition analysis of the samples taken from theingot.
12

3.7 Measurements of Material Properties
The primary objective of the material properties measurements was to expand the databaseobtained during RASPLAV Project. New data were obtained for the C-32 corium and for metallic
phase formed during interaction of molten corium with the steel. The following material properties
were measured:•

Viscosity, density and liquidus temperature for C-32 corium•

Electric conductivity, thermal conductivity, viscosity, and the temperatures for phasetransitions as well as the spreading temperature for metallic phase.

The experimental techniques and the full set of data obtained were presented in the report
MP-TR-12 [9].
The viscosity of C-32 corium was measured using the method of damping of torsional oscillationof a cylinder filled with studied liquid similarly to the measurements performed during the RASPLAV
project. The values of kinematic viscosity for the corium C-32 were measured within the temperature
range 2380-2600 °C. It should be noted that measured viscosity for C-32 corium is very close to thatmeasured earlier for the C-22 corium. Up to 2200°C the system behaves as a solid body and ischaracterized by a low damping factor that is practically independent of the temperature. Under thetemperatures higher than 2370°C, the system is characterized by a high damping factor that decreases
slowly with the temperature increase. This behaviour is typical of normal liquids. Within thetemperature range 2200 - 2370°C, the system is characterized by a noticeable growth of the damping
factor with the temperature increase. This temperature range may be considered as a simultaneous
existence of a solid and liquid phases.
The special facility was developed, designed and fabricated to measure the density by modifiedhydrostatic weighing method. Data on the C-32 corium density were obtained within the temperature
range 2482 – 2585oC. During the RASPLAV Project the C-32 density was also measured
simultaneously with the surface tension. The value for density 7.49 + 0.44 g/cm3 for the temperature of
2470 – 2580oC was obtained which is consistent with the current data.
The liquidus temperature of the corium was measured by three different techniques. These
techniques were developed within RASPLAV&MASCA Projects:•

Viscosity technique•

Gas Bubble Technique•

Thermogram recording technique.

All these three different technique gave very close results presented in Figure 3
The material properties of metallic phase were measured for the samples cut out of the metallic
part of the ingot obtained in the T-7 test. The results of chemical analysis are presented in Table 4.
One of the most important characteristics of the material is electric conductivity. The
measurement of electric conductivity and its temperature dependence allows to judge about the natureof chemical linkage between the components of the studied material. The method employed for the
study consist of the measurements of the Volt-Ampere characteristic of the sample. The temperature
coefficient for specific resistance was determined by the least-squares method. Table 5 presents the
specific resistance of the studied sample under 20°C and the temperature coefficient. Figures in roundbrackets are the measurement errors (dispersion). The same table contains also the values of for pureiron [10], zirconium [11], and uranium [12]. It is seen that specific resistance of the alloy under study13

is very close to that of zirconium and the temperature coefficient of specific resistance – to that ofuranium.
Figure 3. Comparison of Liquidus Measurement by Three Different Techniques

0.1

6

0.5

dT/dτ

0.08

4.5

0.06

3

0.04

0.6

Decrement

PressuredT/dτ ( oC/s)

7.5

Decrement

0.12

Pressure (kPa)

9

0.4

0.3

0.2

2300

2325

2350

2375

2400

2425

Temperature (oC)2450

Table 4. The “Metallic Body” Chemical Analysis
Sample composition (mass %)U

Zr(Zr+Fe+U)free

Fe

C

Nb

O (diff.)

U/Zr(at./at.)

27.2

13.26

*

59.37

0.143

*

0.03

0.79

* - not measured
Table 5. Specific Resistance (ρ) and Temperature Coefficient of that (α) of the Alloyand Its Components
Material

T (oC)

ρ ⋅ 108(Ohm ⋅ m)α ⋅ 103 (1/K)

Reference

Alloy under study
Fe
Zr
U

20
20
27
25

43 (4.3)
9.8
43.5
25 - 34

2.38 (0.17)
6.2
3.8
2 – 2.8

This work
[37]
[38]
[39]

For the thermal conductivity measurement the sample was placed between the heater and heatreceiver. The heater and heat receiver were fabricated from copper to minimize the temperature
gradients. The copper heater was heated by an electric coil. The technique for thermal conductivity
measurement is based on the solution of the non-steady-state heat conductivity equation. The tests
were performed with different power applied to the heater. In Table 6 averaged thermal conductivity
data are presented.

14

Table 6. Thermal Conductivity Data Obtained in Tests
T( C)

Thermalconductivity(W/(m⋅K))

Number ofexperimental
pointsDispersion due
to statistic(W/(m⋅K))

Dispersion due tosystematic error(W/(m⋅K))

Total
dispersion(W/(m⋅K))

1 113 - 201
2 49 - 134
3 152 - 216
4 84 - 174

13.68
12.32
13.39
13.53

989
2075
353
1381

0.39
0.98
0.21
0.42

1.3
1.3
1.3
1.3

1.3
1.6
1.3
1.4

84 – 216

13.53

2753

0.41

1.3

1.4

#

o

The viscosity measurements were performed for the samples synthesized artificially from puremetals. This compound consisted of the uranium, zirconium and iron. The gross formula of thecomposition (U0.44Zr0.56)0.2Fe0.8 is close to that of the sample produced in the T-7 test. The method of
damping of torsional oscillation of a cylinder filled with the melt was used to measure the “metallic
body” viscosity. Up to the temperature 1380ºC, the system behaves as a solid body and ischaracterized by a low damping decrement. Under the temperature higher than 1600ºC, the system ischaracterized by a high decrement factor that does not practically depend on the temperature. This area
may be construed as a liquid with a low fluidity activization energy. The intermediate area of1380 - 1600ºC is characterized by the non-monotone behaviour of the damping decrement and may beconstrued as a two-phase area with simultaneous presence of the solid and liquid phases. Kinematic
viscosity was calculated in the area of the theory applicability. Figure 4 illustrates kinematic viscosity
versus the temperature.
Figure 4. The “Metallic Body” Viscosity versus the Temperature1

viscosity*106 (m2/s)

0.8

0.6

0.4

0.2

0
1500

1600

1700

1800

1900

temperature (C)

2000

2100

The technique for the determination of Tspread of metallic phase consisted in the observation of thesample condition through the optical micropyrometer which allows the observation of the liquid phaseappearance in the form of a film or drops, trickling of that on the surface up to complete melting. The
15

experiment was conducted in the inert atmosphere to prevent the change of chemical composition ofsamples. The temperature increased with a constant rate. The samples of the metallic phase were takenfrom the ingot obtained at the RCW facility.
Table 7. Results on Density, Chemical and X-Phase Analyses of the RCW Ingot
Samples
SampleDensity,
g/cm3

#1
top

9.03

#2
middle
part

9.85

#3
bottom

10.72

Chemical composition, mass%
U

Zr

Fe

Gr

Ni

C

Phase composition and gridparameter,nm(UZr)Fe2(a=0.699)+solid solution
23.09 10.20 43.2 11.55 8.01 0.058 of UO2(a=0.542) +traces ofZr(C,O)(UZr)Fe2(a=0.702)+
solid
38.89 13.53 31.6 8.36 5.43 0.042 solution of UO2(a=0.544) +tracesof Zr(C,O)(UZr)Fe2(a=0.7127)+phaseX+
51.96 20.10 16.6 4.04 2.93 0.19 solid solution of UO2(a=0.545) +Zr(C,O) (a=0.466)

The spreading temperature obtained varied from 17700C in the top sample to 24300C for the samples
taken from the bottom of the ingot.
3.8 Salt Tests
RASPLAV salt tests were an important part of the RASPLAV project. There were two major
goals of those tests, namely (1) justification of the major decisions for the preparation and interpretationof the corium tests, and (2) studies of complementary heat transfer phenomena, which can potentiallyinfluence the analysis and interpretation of tests. The list of phenomena of interest included (a) crust
formation along cooled boundaries of the pool from the eutectic salt mixture, and (b) crust formation from thenon-eutectic composition [13].
The RASPLAV Salt facility was designed to simulate and study thermal processes of interaction
between the molten corium and the reactor vessel wall using molten fluoric salts (NaF-NaBF4, LiF-NaFKF, LiF-NaF-ZrF4). The design of the RASPLAV Salt facility is similar to the RASPLAV corium
facility. The facility represents slice geometry with the characteristic radius of the semicircular sectionof 200 mm. The test wall 20 mm thick was cooled by the secondary salt mixture. The test wall was
instrumented with thermocouples, which allowed to measure temperature and heat flux through the test
wall. Moreover, the moving frame with many thermocouples provided melt pool temperature throughout
the melt volume and boundary layers. Molten salt forming the lower pool was LiF-NaF-ZrF4 with themelting temperature of 558°C, while for the upper pool the composition LiF-NaF-KF with melting
temperature of 454°C was used. The difference in the melting points of both salts was 104°C large enough toallow simulation of peculiarities in the heat transfer. Upon completion of the RASPLAV Project the
RASPLAV-A-Salt was updated to perform the test series specified within the framework of the
MASCA Project.
In the frames of MASCA projects test series at the RASPLAV salt facility were conducted in the two
liquid layers configuration. The objectives of tests were as follows:• Simulation of the focusing effect of the heat flux when the heating of the upper payer is dueto the convective heat transfer from the bottom pool. For these cases the situation with and without

16

top crust is considered. For the first case the convection pattern in the upper layer is uncoupledwith the convection in the lower layer. The second case presents coupled convection in both layers.
Study of the focusing effect as a function of dimensionless numbers such as Biot (Bi) andNusselt (Nuup, Nusd) numbers.
Verification of correlations for upward and downward heat transfer under variable conditions
at the top pool surface from isothermal to almost adiabatic.

••

4. Findings
4.1 Melt Stratification Mechanism
Different possibilities for corium stratification were studied in a series of small-scale experiments.
Stratification observed in the large scale RASPLAV AW-1 test can be explained by small amount ofcarbon 0.3 – 0.4 wt.%. Small-scale experiments indicated that there is some threshold value of about
0.2 wt.% above which carbon produce a top layer enriched with zirconium. Carbon content in theupper layer increases up to 1.5 wt.%, while in the bulk oxide phase the amount of carbon does notexceed 0.1 wt.% [7]. This effect can be explained by the formation of zirconium carbides andoxicarbides.
Figure 5. Carbon Concentration (a) and U/Zr Ratio (b) in the Top and Middle Layers
versus Exposure Time at the Temperature of 2550oC
1.4

1.6

1.2

2

1.2

Top layer
Middle layer

17

Top layer
Middle layer

1

U/Zr

Carbon concentration (mass%)

3

0.8

1

0.8

3

7

0.4
0.6

2
0.4

0
0

20

Time (min)

40

0

60

20

Time (min)40

60

Stratification kinetics was fast enough; the characteristic time varies between 6 and 12 minutes.
As characteristic dimensions of the RASPLAV-AW facility were approximately 4 – 5 times larger
then expected characteristic time for large-scale tests might be 20 times larger (between 2 and 4
hours).
Another mechanism for melt stratification was the influence of the heating up rate which maylead to separation of corium components. This mechanism was partially confirmed by experiments
performed in the STFM-2 series. At the temperature of 2200oC the upper part of ingot was enrichedwith zirconium based phase ZrOx with relatively small amount of uranium. At this temperature level
the ratio of areas occupied by light and gray phases reached the value of 1.4 (Experiment STFM#2/3)
while the average value at higher temperature was about 0.5 – 0.6. However experiments showed that
this stratification was unstable; increase of temperature up to 2500oC led to practical disappearance ofthe differences between upper layer and bulk corium.

174.2 Interactions of Corium with Steel (Iron)
In a series of small and middle scale tests with iron and stainless steel it was clearly demonstrated
that molten steel (iron) extracts some metallic zirconium and uranium from suboxidized corium
leading to the increase of metal phase mass and density and consequently to a possible change of layer
configuration [14, 15, 16, 17, 18]. Uranium transport to the metallic phase is closely related to theexistence of free zirconium in the initial suboxidized corium. The amounts of U and Zr atoms
transferred to the metallic phase depend upon metal mass and corium oxidation degree.
Steel concentration increases with the increase of the relative steel content in the corium, but theconcentration of uranium and zirconium is decreasing with the increase of the steel (iron) content in
the tests.
Concentrations of U and Zr decrease with the increase of zirconium oxidation degree. There isalso some dependence upon metal content, however this dependence is rather weak. The ironconcentration increases gradually with the increase of the zirconium oxidation degree and also ironconcentration is increasing with the increasing of the mass of metal added to the melt.
A very small amount of iron goes into the oxide phase (less than 1% wt.). After interaction, thedegree of oxidation of the oxide phase is increased. Increasing of steel to corium ratio leads toincreasing of oxide phase oxidation degree approaching almost complete oxidation for large amountsof steel (iron) content in the test.
Density of metal phases depends mainly on the ratio of U to steel or iron while the most relevant
factor for oxide phase density is corium oxidation degree.
4.3 FP Partitioning
Sufficient improvement of the knowledge of fission product spatial and chemical distributions in
the melt pool was achieved in the MASCA Project. It was confirmed that there is a partition of thefission products between the metallic and oxidic phases. Elements with a stable oxide form under thetest conditions can be found essentially in the oxide phase, while the other elements are found in themetallic phase. In each respective phase, the elements are uniformly distributed. For the compositions
studied, the distribution of fission products between the oxidic and metallic liquids is in agreementwith the predictions of thermodynamic calculations [19]The FP partitioning coefficient between the oxidic and metallic phases Ko=Xmet/Xcor, depends onthe melt parameters such as temperature, corium oxidation degree, U/Zr ratio.
4.4 Migration of Molten Metal Through Porous Oxide Debris
Molten steel demonstrated good ability to penetrate into the corium if the temperature of steel
exceeds its melting point by 350 K. At the temperature of 1600°C steel penetrated only if the size ofpores is large enough. However at temperature higher than 1800°C, steel penetrate not only in thedebris formed by particles of 1.2 - 3.5 mm, but also through the corium briquettes with the low
porosity (about 10%). TULPAN T-8 test conducted in the vertical temperature gradient indicated thatthe penetration of steel was observed up to the temperature about its melting point [5].
However the composition containing the alloy of stainless steel and zirconium(85 % SS + 15 % Zr) demonstrated weak wettability and consequently the penetration ability even in
the cases when superheating above the melting point was 400 – 500°С. The wetting angle wasassessed to be ~ 150°.
Improvement of understanding about the zirconium and stainless steel alloy penetration into theporous medium of the corium particles, it seems expedient to continue studies in the line of thetemperature range increase (up to 2300°C) and employment of other alloys composition.
18

At low temperature, slightly above steel melting (1900K), a limited interaction was observed
between steel and partially oxidized corium debris (solid). There was formation of Fe-Zr and F-U
eutectic mixtures. For fully oxidized debris, no interaction was observed. Similar observations at
higher temperatures would be interesting to quantify the kinetics of interactions between liquid steel
and solid corium (tests described above have shown that the liquid-liquid interaction at hightemperature is rather fast to reach equilibrium).
Debris experiments have also shown that the progression of molten steel into the debris bed islimited by capillarity and wettability effects which become important for small particles (2-3 mm).
This shows that, at low temperature, the phenomena governing metal progression into the oxide debris
are more important than the chemical phenomena to determine the total amount of dissolved materials.
Such transient effects need further investigations.
4.5 Boron Behaviour and Its Impact on the Stratification
The performed tests have shown that boron carbide decomposes on contacting the suboxidized
C-32 corium under the temperature lower than 1800oC generating mainly zirconium oxycarbide anddiboride. On introducing small quantities of B4C into the corium composition, a significant nonuniformity in boron partitioning along the ingot height takes place due to the melting. The upper zone
is enriched in boron mainly in the composition of the refractory compound ZrB2 [8].
The introduction of 0.5 mass% of B4C into the C-32 corium results in the considerable increase of
the produced liquid-metal phase due to the interaction with the melt based on Fe. The produced
metallic ingot is enriched in boron and zirconium that results in significant reducing of its density.
This results in the fact that the oxidic corium composition shifts to that of the C-100 corium.
Several tests conducted with a boron carbide addition (which may come from molten controlrods) demonstrated peculiarities of the behavior of oxide and metal phases. For the suboxidized
corium the effect of boron carbide was similar to chemical effects observed in the RASPLAV tests
with carbon. Zirconium carbides and borides were observed in the post-test examination of ingots.
With an addition of iron, the effect of phase separation became more pronounced. The amount ofmetal phase became larger, new phases were also observed. This effect needs further investigations.
5. Conclusions
In the framework of MASCA Project the technology has been developed to conduct the hightemperature corium tests including design, fabrication and assembly of a large-scale facility capable toheat up and retain molten corium and steel at relevant temperatures under controlled conditions. The
experimental facilities used in MASCA are actually well suited for the study of any metal-oxide
mixture at high temperature because the interactions between the corium and the crucible are very low.
Sufficient improvement of the knowledge have been achieved on the following items:• Melt stratification mechanisms;• Stratification phenomenon in iron containing melts;• Fission product spatial and chemical distribution in the melt pool;• Molten metal migration into the debris bed;
• Boron effect on the stratification.
The discovered and quantified phenomena of component partitioning between the oxidic andmetallic phases during the interaction of suboxidized corium and steel can be used for thedevelopment and verification of corresponding models describing the molten pool behaviour. Precise
measurements of the material properties and the composition of metallic and oxidic phases provide
important data for validation of thermodynamic databases.
19

The MASCA Project results obtained with corium compositions prototypical of power reactors
would provide qualitative and quantitative data for assessments of the in-vessel melt pool retention
strategy as well as for ex-vessel phenomena.
Nevertheless new studies will be needed to reduce a number of uncertainties including
uncertainties on the phase equilibria for U-Zr-O-Fe mixtures, on the physical properties of mixtures
and alloys (liquidus and solidus temperatures, densities, thermal conductivity, viscosities), anduncertainties about the transposition of MASCA results to models for reactor cases, including scaling
effects, the influence of an oxidizing atmosphere and the impact of non-uniform temperatures.

20

References

1

T.Okkonen, In Vessel Core Debris Cooling Through External Flooding of the Reactor
Pressure Vessel, presented at the OECD/CSNI/NEA Workshop on Large Molten Pool Heat
Transfer, Grenoble, France, March 9-11, 1994. pp.29-42.

2

L.Baker, Jr. et al. Heat Removal from Molten Fuel Pools, Proceedings of the International
Meeting on Fast Reactor Safety and Related Physics, Chicago, Illinois, 1978.

3

G.Keyser, The SCARABEE BF1 Experiment with a Molten UO2 Pool and its Interpretation,
presented at the OECD/CSNI/NEA Workshop on Large Molten Pool Heat Transfer, Grenoble,
France, March 9-11, 1994. pp.207-225.

4

RASPLAV Application Report, OECD RASPLAV Seminar, Munich, 2000.

5

V. Asmolov, Yu. Degaltsev, O. Schakh, S. Abalin, I. Semenov, I. Isaev, K. Pechalin,
B. Gershman, A. Ignatochkin, A. Grafsky, V. Vlasov, Yu. Utkin, A. Kovalev, Study of the
Molten Metal Migration in the Oxide Porous Matrix, MP-TR-5, July 2003

6

B. Adroguer, Impact of B4C Control Rods on the Core Degradation under Severe Accident
Conditions, 9th PRG RASPLAV Meeting, Cadarache, 14-16 Oct. 1998.

7

V. G. Asmolov, Ye. V. Astakhova, Yu. G. Degaltsev, Ye. K. Dyakov, A. Yu. Kotov,
V. M. Repnikov, T. V. Trushkina, V. V. Vlasov, V. Yu. Vishnevsky, Yu. M. Utkin,
V. N. Zagryazkin, Study of Carbon and Separation Impact on Suboxidised Corium
Stratification, MR-TR-2, June 2001г.

8

V.G. Asmolov, Ye.V. Astahova, V.Yu. Vishnevskiy, E.K. Dyakov, V.N. Zagryazkin,
A.Yu. Kotov, V.M. Repnikov, Investigation of B4C Impact on U-Zr-O Corium Stratificationand the Processes of Its Interaction with the Melt Based on Fe, MP-TR-7, September 2002

9

V.Asmolov, S.Abalin, S. Beshta, A.Merzlyakov, V.Vishnevsky, A.Kotov, V. Repnikov,
Measurement of Physical Properties, MP-TR-12, June 2003

10

N.I. Koshkin, M.G. Shirkevich, Handbook on Elementary Physics, Moscow, Nauka, 1972,(Russ.)

11

V.E. Peletzkii, E.A. Belskaya, Electrical Resistance of Refractory Metals, Moscow,“Energoizdat”, 1981. (Russ.)

12

J.J. Katz, E. Rabinovitch, The Chemistry of Uranium, v.1, NY, 1951.

13

V.Asmolov, S.Abalin, A. Surenkov, I.Gnidoy, B.Barkovsky, N.Komissarova, D.Chuvilin,
Yu.Rybakov, V.Strizhov, V.Semenov, Study of Thermal Hydraulic Processes in a Stratified
Molten Pool, MP-TR-13, December 2003

14

V. Asmolov, V. Khabensky, S. Beshta, V. Gusarov, S. Vitol, Ye. Krushinov, Yu. Degaltsev,
V. Vlasov, Yu. Utkin, MA-1 Experiment: Post-Test Analysis Results, MP-TR-1, November
2001

15

V.G. Asmolov, V.B. Khabensky, S.V. Bechta, S.A. Vitol’, E.V. Krushinov, S.Yu. Kotova,
E.K. Kalyago,
N.E. Kamensky,
A.V. Lysenko,
V.G. Bliznyuk,
V.R. Bulygin,
E.V. Shevchenko, V.S. Granovsky, V.V. Martynov, V.V. Gusarov, V.I. Al’myashev,
M.D. Tolkachyov, M.R. Pavlov, V.V. Vlasov, Yu.G. Degaltsev, Yu.M. Utkin, The MA-2
Experiment: Zirconium and Uranium Partitioning between Oxide and Metallic Phases ofMolten Corium, MP-TR-6, March 2002
21

16

V.Asmolov, V. Khabensky, S. Beshta, Ye.Krushinov, S.Vitol, V.Gusarov, S.Yu. Kotova,
V. Almyashev, Yu.Degaltsev, The MA-3 and MA-4 Tests: Zirconium and Uranium
Partitioning between Oxide and Metallic Phases of Molten Corium, MP-TR-9, February 2003

17

V.G. Asmolov, Ye.V. Astahova, V.Yu. Vishnevskiy, Yu.G.Degaltsev, E.K. Dyakov, V.N.
Zagryazkin, A.Yu. Kotov, V.M. Repnikov, T.V. Trushkina, Yu.M. Utkin, V.O. Chernyshov,Study of the Liquid Steel Behaviour in the Molten Corium in STFMFe Test Series, MP-TR-8,
February 2003

18

V.G. Asmolov,
S.S. Abalin,
Yu.A.Veselkin,
V.Yu.
Vishnevskiy,
V.V. Vlasov,Yu.G. Degaltsev, Ye.K. Dyakov, I.F. Isaev, A.N. Kiselev, N.P. Kiselev, A.M. Kovalev,
A.G. Ol'khovsky, K.V. Pechalin, I.M. Semenov, V.F. Strizhov, T.V. Trushkina, V.S. Uglov,Yu.M. Utkin, V.V. Chudanov, A.E. Aksenova, V.A. Pervichko, I.M. Khazanovich, RCW
Post-Test Analysis Results, MP-TR-11, September 2003

19

V.G. Asmolov, Ye.V. Astahova, V.Yu. Vishnevskiy, E.K. Dyakov, V.N. Zagryazkin, A.Yu.
Kotov, V.M. Repnikov, V.S. Uglov, Yu.G. Degaltsev, Yu.M. Utkin, T.V. Trushkina,
Partitioning of Fission Products between the Corium Melt Metallic and Oxidic Phases
Resulting from the STFM-FP Tests, MP-TR-10, June 2003

22