Quality Improvements of Thermodynamic Data applied …€¦ · · 2015-11-09Quality Improvements of Thermodynamic Data applied to Corium Interactions for Severe Accident Modelling

ERMSAR 2013, Avignon, October 2-4, 2013

Quality Improvements of Thermodynamic Data applied toCorium Interactions for Severe Accident Modelling in

SARNET2S. BAKARDJIEVA, P. BEZDICKA - UACH, Rez (CZ),M. BARRACHIN - IRSN,Cadarache (FR),S. BECHTA*, V. KHABENSKY - Aleksandrov RIT/NITI, Sosnovy Bor, (RU),M. KISELOVA, V. TYRPEKL*** - UJV, Rez (CZ),D. BOTTOMLEY,T. WISS, D. MANARA - ITU Karlsruhe (DE),C. JOURNEA, P. PILUSO, L. BRISSONNEAU, - CEA-DEN, Cadarache (FR),B. CHEYNET, E. FISCHER, - Thermodata, St. Martin d'Hères (FR),O. DUGNE, - CEA-DEN, Marcoule (FR),M. FISCHER , - AREVA-NP, Erlangen (DE),V.GUSAROV** - Inst. Silicate Chem.-RAS, St. Petersburg (RU),M. SHEINDLIN, - IVTAN-RAS, Moscow (RU)

*now at KTH Stockholm (Swe),** now at Joffe Physical Technical Institute (RU),*** now at ITU Karlsruhe (DE).


OUTLINE

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Introduction

Testing

– NUCLEA Database

– Small scale testing

ITU (refractory phase melting data),

UJV & UACH, Rez (ex-vessel system testing, COMETA),

IVTAN – Laser flash (CaO)

– Large scale testing

VULCANO facility VBS-U3 test (silicaceous concrete, + metallic & oxidic corium)

NITI, Sosnovy Bor: CORPHAD–PRECOS Projects (IMCC furnace)

AREVA GmbH- EPICOR Tests (RASPLAV-3 facility- NITI)

– Applications to the Database

UO2-ZrO2-FeO, UO2-CaO

Conclusions


Introduction

In a severe accident, corium composition and its propertiesdetermine its behaviour and interactions with the reactorvessel and later with the concrete basemat.

This requires a detailed knowledge of the high temperaturephases and chemical reactions

Such HT data are often difficult to obtain or poorly known.

Obtaining such data is the objective of this MCCI workpackage (WP6) of SARNET 2 Network of Excellence.

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NUCLEA Database

NUCLEA is a thermodynamic database for nuclearapplications, with a self-consistent database with 18 elementsand more than 300 assessed binary or ternary systems.

NUCLEA contains18 (Al-Si-Mg-Ca-U-Zr-O-Fe-Ni-Cr-Ag-In-B-C-Sr-Ru-La-Ba)+ 2 elements (H, Ar). Critical assessments madeon many compounds and systems

Thermochemical equilibrium state of a system calculated withGEMINI2 code, (Gibbs Energy minimisation approach) at anystep.

This requires a detailed knowledge of the high temperaturephases and chemical reactions.

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Experiments at ITU - laser flash facility

Examination of UO2-ZrO2-FeO system by laser flash pyrometry

(FeO from 10 to 80 mol%)- an important in-vessel degradation system

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ITU's Laserflash pyrometryfacility



Examination of the UO2-ZrO2-FeO system by laser flash pyrometry

(xUO2-xZrO2-(1-2x)FeO; FeO from 10 to 80 mol% - an important in-vessel degradationsystem)

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Thermogram from laser flash heating of a45%UO2-45% ZrO2-10mol%FeO sample.The blue trace is the reflected laser scattering (RLS)- indicates liquid phase is present.The black line shows the laser power profile.

3020K inflexion -1st freezing of UO2–rich-ZrO2

phases2700K inflexion – freezing of (remaining)

equimolar UO2-ZrO2 phases2400K inflexion– freezing of UO2-ZrO2-FeO

phases.~1640K – no inflexion from FeO-dominated

phases



Examination of 45%UO2-45%ZrO2-10mol%FeO by laser flash pyrometry

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Optical macroscopy 45%UO2-45% ZrO2-10mol%FeO after 3 laser flash shots (left). SEM micrograph (right)shows the molten zone and unmelted material beneath; table gives EDS analysis of 3 melt zones


Experiments at UJV & UACH Rez - Cometa Facility

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Scheme of the COMETA facility.1 melting chamber with illuminators2 supporting movable frame3 cold crucible4 inductor5 high frequency generator6 drive mechanism for moving frame (2)7 ball-&-screw couple of the moving mechanism8 ventilator of the gas –purification system9 filter10 water-cooling system11 aerosol sampler12 radiation pyrometer or videocamera13 PC-based information and measuring system.

Samples from 18 experiments were examined upto 3273Kin the SARNET 2 project: U-Zr-O, U-Fe-Zr-O, U-Fe-Zr-Si-Ca-O, U-Fe-Zr-Si-Ca-Al-O systems for in-and ex-vesselsystems in oxidising conditions. Concrete compositionschosen in conjunction with VULCANO test.

ERMSAR 2013, Avignon, October 2-4, 2013 9

Photos of the ingots from URAN 24 and 25 experiments. Thecircles indicate the areas for post –test sampling and analyses

UJV titleCEAtitle

Atmosphere Composition [wt%] T [°C] Note

URAN 24 / 25 VB-U6 air

39,2 % UO2 20,2 % SiO2

28,4 % ZrO2 3,7 % Fe2O3

7,3 % CaO 1,2 % Al2O3

~ 1900-2100

(max.

2186 / 2120)

Expt. performd 2x,

U24 explosion,

zonal (slow)

crystallization

Table showing conditions of URAN 24 & 25 tests



Experiments at UJV-Cometa Facility

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Micro-structure of the URAN 25 quenched sample. Note the primary dendrites of U,Zr-rich phasesfrom the liquid + very fine secondary dendrites projecting into remaining liquid,whose composition is shifting steadily towards a light liquid composition of MeO2 (Me=Fe, Al)


Micro-structure of the URAN 25 ingot sample, showing:a) high melting MO2 (M=U,Zr) crystals (with zonal enrichment of Zr in the centre) and,b) fine dendrites of the crystallized associate phases MeO1.5, where Me = Al, Fe) and,c) (dark) residual phase enriched in Si & Ca.



Micro-structure of the URAN 25 ingot sample, showing:a) high melting MO2 (M=U,Zr) crystals (with zonal enrichment of Zr in the centre) and,b) fine dendrites of the crystallized associate phases MeO1.5, where Me = Al, Fe) and,c) (dark) residual phase enriched in Si & Ca.

Division into 2 phases dependent on the Si content was noted: a) areas with a low Ca3SiO5 content and with (U,Zr)O2

crystalline phases and crystallized phases of the (U,Zr)O2-SiO2 eutectic system; 2) areas with higher content ofCa3SiO5 containing (U,Zr)O2 but with Ca2SiO4 dendritic crystals and Fe3O4+Ca(U,Zr)O4 phases appeared.No influence of Al2O3 on phase composition during cooling was observed.



Experiments at CEA, VULCANO Facility

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The VULCANO furnace facility at CEA Cadarache



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VBS-U3 post-test dismantlingleft: cross-section of ablated concrete test section;right: the estimated ablation profiles in different radial directions

The VBS-U3 test used a siliceousconcrete:12.89% wt Ca(OH)2,16.2% wt CaCO3,65.89%wt SiO2,2.87%wt free H2O,2.15wt% Al2O3.

Added metallic load was:15kg PWR stainless steel(69.62 wt%Fe, 18.20 wt%Cr, 9.20 wt%Ni, 0.028 wt%S, 0.038wt%P,1.92 wt%Mn, 0.92 wt%Si, 0.075 wt%C)+ 91 kg of oxidic corium(69 wt% UO2,17 wt % ZrO2, 6 % wt SiO2,7% wt Fe2O3, 1% CaO).Liquidus temperature of 2460 K.



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Note the uneven ablation profile of VBS-U3 witha) corium & degraded concrete crust.b) corium is mainly oxidic but base is metallicc) particularly large amount of metallic phase with locally enhanced radial & axial ablation.d) a wall of metallic phase on one side.e) large cavity in the oxidic corium pool.

VBS-U3: Cross-section of theasymmetric corium pool ablation ofthe concrete test section, showingthe local analysis where furthersampling was made and some ofthe key results



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VBS-U3- Metallic drop floating on anoxidic pool; densities are indicated withthe phases

a) solutal convection occuring ie. different phases are slowly mixing, despite the different compositionaldensities.b) corum-rich (oxidic) zones in the pool had typically 82 mol % (U,Zr)O2, thus oxidic density >metallic drop.concrete–rich oxidic melts, metallic drop had only 49mol% (U,Zr)O2 thus metallic droplet density > concreterich melt.c) Metallic nodule (above) is clearly seen sitting in the middle of a concrete rich melt, supports this.d) Furthermore, stratification in a reactive pool is likely thus constantly changing compositionpossible.



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VBS-U3- Metallic dropfloating on an oxidic pool;densities are indicated withthe phases

Conclusiona) overall geometry indicates greater ablation rates by metallic than by oxidic melts,b) following ranking of local ablation rates in the concrete:

axial ablation by oxide < lateral ablation by oxide<axial ablation by metal < lateral ablation by metal


Experiments at NITI, Sosnovy Bor:CORPHAD–PRECOS Projects

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1 water-cooled calorimeter;2 water-cooled pyrometer shaft;3 pyrometer coupled with videocamera;4 data acquisition system;5 device for insertingmeasurements into video frames;6 monitor/video recorder;7 crucible vertical drive.

IMCC Furnace diagram



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Micrographs of samples 1 & 2 from 50%UO2-50%CaO melt with ingot SEM/EDX analysispoints

A polished section from 50%UO2-50mol%CaO



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Thermogram of pure CaO heated by laser flash technique

CaO melting temperature =2900± 15С (cf. theo. mp of >3100K).previous values much lower

CaO is difficult to measure since:a) also optically (IR & visible)

transparent above ~2000Kb) melting temp. is close to the

boiling temp. hence canvolatilize rapidly duringmeasurement,


AREVA NP GmbH - EPICOR Tests

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Formation of a dense metal phase

In all EPICOR tests, the initial composition and state of the sub-oxidic systemwas the same with a U/Zr atomic ratio of 0.83 (BWR), a melt temperature of2450(±50)°C, and a corium oxidation index of C-35.

EPICORFor validation of the In-Vessel Melt Retention (IVR) strategy in BWR, AREVANP examined formation of dense metallic phases which can lead to a largeincrease in local heat fluxes, with the risk of early IVR failure.Using an improved “cold crucible” technique, two series of tests, with a lowU/Zr-ratio and high contents of Zr, steel, ±1.4 wt% B4C content were performed.

Oxidation index


AREVA NP GmbH - EPICOR Tests

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Analysismetallic melt:borides and intermetallics: B2Zr, U(Zr)Fe(Ni,Cr)2, Zr(U)Fe(Cr,Ni)2, &Fe3Cr; no carbide-based phases were found.oxidic melt:solid solutions based on (U,Zr)O2 and (Zr,U)O2; -Zr, andZr(U)Fe(Cr,Ni)2-based intermetallic phases were found.

Test ER-4 ingota) schematic cross-section after

solidification with oxidic melt belowand metallic “lense” above,surrounded by an oxidic crust

b) metallic part, with shrinkage poreand venting channel.

a b


Improvements of the NUCLEA databasea) Modelling of UO2-ZrO2-FeO system

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Comparison of experimental withNUCLEA calculations in the UO2-ZrO2-FeO system showing theliquidus and solidus temperaturesversus FeO content in the xFeO-(1-x)/2UO2-(1-x)/2ZrO2 system

AnalysisGenerally good agreement between exptl. &theo. values,esp. FeO mp. at ~1600K and for the mixedZrO2-UO2 phases.some phase segregation in the mid-range(40-80 mol%FeO) as the refractory UO2-ZrO2

behaviour dominates (U-rich phasesseparate to produce very high initialfreezing).Note no FeO freezing seen at <20mol%


Improvements of the NUCLEA databaseb) Modelling of the UO2-CaO phase diagram

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Updated version of the UO2-CaO pseudo-binary system (neutral atmosphere.Phase transition temperatures are measured by different methods (XRF,SEM/EDX and chemical analysis of corium samples).CaO melting temperature is determined by IVTAN (laser flash Pyrometry). Thehigh experimental value has confirmed the theoretical predictions and retained inthe NUCLEA database.


Improvements of the NUCLEA databasec) AREVA – effect of B in corium layer Inversion

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Densities of the oxidic &metallic liquids; B4C content0-1.37 wt% of the initialoxide mass.Model assumption all boroncarbide partitions into themetallic melt and stays there as

a substance.Note no inversion point forB4C = 1.37%

In addition- calcs. considerably overestimate (by

up to 12 wt%) the U-content inmetallic liquid compared to exptl.findings.

- On the contrary, the Zr-content inmetal is substantially underestimated(by up to 5 wt%) compared toexperiment.


Improvements of the NUCLEA database

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• Very distinctive anisotropy that is until now has no established cause although severalmechanisms appear possible (eg crust structure differences on vertical and horizontalsurfaces.

• Finding of chromium trioxide (CrO3) suggest unexpectedly highly oxidised conditions locally,close to a reduced form (CaSiO0.5). If this is reproduced, it would suggest greater variationand very localised chemical processes occurring in the melt.

• Effects and the longer term impact are impossible to assess by simpler 2-D modelling ortests.

• Future tests: the modelling of reinforced concrete and the effect of rebar in creating unevenheat fluxes at the interface. This needs 3D testing.

e) UJV & UACH Rez, UO2-SiO2-CaO ex-vessel coria

• They show separation into heavy [(U,Zr)O2-based] & light melts with high and low Ca contents.Areas with low Ca3SiO5 content form additional (U,Zr)O2-containing phases (+ SiO2)phases;Areas with higher Ca3SiO5 content form additional Ca2SiO4- containing dendrites with(U,Zr)O2, Fe3O4 and Ca(U,Zr)O4 phases.

• Light liquids appear between the primary (U,Zr-rich) dendrites of formula MeO1.5 (Me= Fe,Al).• Al2O3 appeared to play little role in the phase formation.

d) CEA Cadarache- Complex ex-vessel coria


Improvements of the NUCLEA database

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• Very distinctive anisotropy observed has no established cause - several mechanismspossible (eg crust structure differences on vertical vs. horizontal surfaces.

• Finding of chromium trioxide (CrO3) suggest unexpectedly highly oxidised conditions locally;this suggests greater variation and very localised chemical processes occurring in the melt.

• Effects and the longer term impact are impossible to assess by simpler 2-D modelling ortests.

• Future tests: the modelling of reinforced concrete and the effect of rebar which results in anuneven heat fluxes at the interface. This needs 3D testing.

e) UJV & UACH Rez, UO2-SiO2-CaO ex-vessel coria

• They show separation into heavy [(U,Zr)O2-based] & light melts with high and low Cacontents.

Areas with low Ca3SiO5 content form additional (U,Zr)O2 crystalline phases and(U,Zr)O2-SiO2 eutectic crystallized phases;Areas with higher Ca3SiO5 content form additional (U,Zr)O2 and Ca2SiO4 dendriticcrystals but also Fe3O4 and Ca(U,Zr)O4 phases.

• Light liquids appear between the primary (U,Zr-rich) dendrites of formula MeO1.5

(Me= Fe,Al).• Al2O3 appeared to play little role in the phase formation.

d) CEA Cadarache- Complex ex-vessel coria


Conclusions

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• Research in WP6 molten corium concrete interaction (MCCI) for the SARNET2 project andassociated ISTC projects has shown significant progress in understanding physicalchemistry of high temperature corium melts and in quality improvement of data used forthermodynamic modelling of severe accident phenomena.

• Large facility testing in MCCI erosion has demonstrated (non-predictable) anisotropy effectsand shows how variable the local conditions can be. Crust stability or structure, gravityeffects need to be understood.

• Cold crucible experiments (under MASCA /OECD programs) have confirmed componentpartitioning between oxidic and metallic liquids and that they have density effects directlyinfluencing layered molten pool behaviour. In particular effects of B4C on chemicalequilibrium and densities of the U-Zr-Fe-O system have been established.

• Examples of the applications of this data to validate the thermodynamic models & databanks(NUCLEA-GEMINI-2) have been given (eg. CaO-UO2 & UO2-ZrO2-FeO phase diagramimprovement). These can improve severe accident predictions.

Documents

Quality Improvements of Thermodynamic Data applied …€¦ · · 2015-11-09Quality Improvements of Thermodynamic Data applied to Corium Interactions for Severe Accident Modelling