ERMSAR 2012, Cologne, March 21-23, 2012

Overview of the ASTEC V2.0-rev1 validation

P. Chatelard (IRSN), S. Arndt (GRS), B. Atanasova (INRNE)

G. Bandini (ENEA), A. Bleyer (IRSN), T. Brähler (RUB)

M. Buck (IKE), I. Kljenak (JSI), B. Kujal (UJV)

ERMSAR 2012, Cologne, March 21-23, 2012 2

Introduction to the ASTEC validation strategy

Examples of the assessment of some ASTEC V2.0-rev1 modules by SARNET partners

– Core degradation module

– Containment module

– MCCI module

Summary of the ASTEC V2.0-rev1 assessment

Conclusion and perspectives

Contents

ERMSAR 2012, Cologne, March 21-23, 2012 3

ASTECcontext and objectives

IRSN-GRS cooperation since 1996 for development of an integral codeASTEC (Accident Source Term Evaluation Code) for present/future nuclear water-

cooled reactors (PWR, BWR, VVER, CANDU) source term severe accident calculation, from initiating event until radioactive release out of the containment:

– Evaluation of source term

– PSA level 2 studies (PSA-2)

– SA management (SAM) evaluation

– Support of experimental programmes

Progressive evolution in recent years towards a state-of-the-art tool for source term calculations:

– Most modeling is mechanistic, only sometimes simplified– Repository of knowledge of severe accident phenomenology

ASTEC = Reference European code in the SARNET network

New series of ASTEC versions (V2 series) since 2009– Mid-2009 : V2.0 First V2 validation by several partners (SARNET2 1st

period) – Mid-2010 : V2.0-rev1 Extended V2 validation by number of partners (SARNET2 2nd period) – End-2011 : V2.0-rev2 Validation to be continued in the frame of SARNET2 3rd period

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ASTEC V2A new series of versions (1/2)

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ASTEC V2.0-rev1validation strategy

Three-tier validation approach (made possible since ASTEC is very modular)– Separate-Effect-Tests focusing on only 1 physical phenomenon– Coupled-Effect-Tests focusing on a set of physical phenomena– Integral tests to check the coupling of physical models and that no essential phenomenon was

forgotten or neglected

Very large ASTEC V2 validation matrix covering all SA phenomena and including major (past, on-going) French, German and international exp. Programs (including VVER experiments), such as in particular:

– All Phebus FP experiments;– Many ISPs: 27 (BETHSY), 33 (PACTEL), 31-36 (CORA), 34 (FALCON), 35 (NUPEC), 37 (VANAM),

39 (FARO), 40 (STORM), 41 (ACE-RTF, CAIMAN), 44 (KAEVER), 45 (QUENCH-06), 46 (Phébus-FPT1), 47 (TOSQAN-MISTRA-ThAI), 49 (ThAI-Enaceff);

– OECD projects: LHF-OLHF, RASPLAV/MASCA, OECD-CCI;– Circuit experiments: BETHSY, ROSA, PACTEL, LOFT-FP, … as well as the TMI-2 scenario – On-going and future new experiments: LIVE on corium pools, PRELUDE, DEBRIS & PEARL on

reflooding, DISCO on DCH, ThAI on containment, EPICUR, CHIP & THAI on iodine, RUSET on ruthenium, VULCANO on MCCI…

The multi-partners validation of ASTEC V2.0-rev1 revision is briefly illustrated in the following through few calculation examples

3 different ASTEC modules have been selected for that purpose

ERMSAR 2012, Cologne, March 21-23, 2012 6

Example of core degradation module assessmentPhébus FP bundle experiments

Phébus FPT3 (work performed by ENEA)

Reasonable agreement on thermal behaviour as well as on both oxidation and relocation processes using the new ICARE 2D magma relocation model which is the one recommended by IRSN for plant applications

Bundle temperature at 0.6 m Total hydrogen production

ERMSAR 2012, Cologne, March 21-23, 2012 7

Example of core degradation module assessmentPhébus FP debris experiment

Material distribution at the end of the test

Phébus FPT4 (work performed by IKE-Stuttgart)

Very good agreement (all along the transient up to the end of the test) still using the ICARE advanced 2D magma relocation model

-0.04 -0.02 0.0 0.02 0.04

Radius / m

0.0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

He

igh

t / m

0.050.100.150.200.250.300.350.400.450.500.550.600.650.700.750.800.850.900.95

VolumeFraction

Time=15500s

lower edge ofdebris bed

lowest meltpenetration

0.0

0.1

0.2

0.3

molten pool

void

upper edgeof pool

-0.04 -0.02 0.0 0.02 0.04

Radius / m

0.0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

He

igh

t / m

0.050.100.150.200.250.300.350.400.450.500.550.600.650.700.750.800.850.900.95

VolumeFraction

Time=15500s

lower edge ofdebris bed

lowest meltpenetration

0.0

0.1

0.2

0.3

molten pool

void

upper edgeof pool

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

0 5000 10000 15000Time (s)

Tem

per

atu

re (

K)

50 mm

153 mm

193 mm

322 mm

heating power

Temperatures at the bed centerline

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Example of containment module assessment KAEVER experiments

Pressure evolution Dry aerosols concentrations

KAEVER K123 (test with CsI aerosol in non-saturated atmosphere)

(validation work performed by JSI)

Th. Hydraulics : Very good agreement on pressure & atmosphere temperat.

Aerosols : Very good trend and good order of magnitude for dry aerosols

But results are generally less good for wet aerosols

0 5000 10000 15000 20000 250000

1

2

3

4

K123 experiment ASTEC v2R1

Pre

ssu

re [

bar

]

Time [s]

15000 20000 2500010-6

1x10-4

10-2

100

K123 experiment ASTEC V2R1

Dry

aer

osol

con

c. [g

/m3 ]

Time [s]

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Example of containment module assessment MISTRA spray experiments

Atmosphere temperatures in radius R4 Sump water level

MISTRA MASP1 (validation work performed by GRS)

Main Th.Hydraulics effects of spray (pressure, atmosphere drops) are well matched by the CPA module from ASTEC V2.0-rev1

But temperature stratification is overestimated by ASTEC

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Example of containment module assessment PANDA SETH free-plume experiments

Test configuration for PANDA test n°18

Steam concentration along the central axis of DW2

PANDA test-18 (validation work jointly performed by IRSN & INRNE)

Reasonable agreement obtained with the CPA module of ASTEC V2.0-rev1 using a refined nodalisation in vertical direction and nodes to model upward plumes recommended nodalization for plant analyses

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Example of H2 combustion module assessment BMC experiments

Tested nodalisations Pressure evolution in room R7

where mixture was ignited

BMC Ix9 (validation work performed by RUB)

Sensitivity study on the nodalisation scheme using FRONT model in CPA:

1. Nodalisations A and B : cutting only in horizontal direction (resp. 4 or 8 zones)

2. Nodalisation C : idem A with an additional cutting in vertical direction

Nodalisation influences the convection and therefore the burning rate

Overall, ASTEC V2.0-rev1 results are in good agreement to the experiment

0.8

1.0

1.2

1.4

1.6

1.8

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

pre

ssu

re [b

ar]

time [s]

Nodal_A

Nodal_B

Nodal_C

experiment

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Example of MCCI module assessment CCI experiments

Vertical erosion depth Final cavity shape

CCI-5 (validation work performed by UJV)

Quite good results have been achieved with the MEDICIS module of ASTEC V2.0-rev1, using a set of input parameters very consistent with the IRSN recommendations for plant applications

ERMSAR 2012, Cologne, March 21-23, 2012 13

Summary of the ASTEC V2.0 assessment

Th.hydraulics in circuits– Good results on SETs and reasonable results on integral tests (including

CESAR-to-CATHARE detailed benchmarks on SGTR scenarios)

Core degradation

– Good results for both early-phase models (heat-up, H2 production, …) and late phase models (2D relocation, molten pool, corium in lower head, …)

– Poor results in case of a reflooding of a degraded core

FP release– Very good results for volatile and semi-volatile FPs and reasonable results

(slight underestimation) for the low-volatile FPs

FP transport– Reasonable results on FP transport and chemistry

But the importance of the gas chemistry kinetics has been underlined, in particular with respect to the final ST (for instance, iodine partition at the break)

ERMSAR 2012, Cologne, March 21-23, 2012 14

Summary of the ASTEC V2.0 assessment

Containment

– Reasonable results on both thermal-hydraulics and aerosols behaviour

– Poor results on pool-scrubbing phenomena

DCH

– Current models are still too parametric and too geometry-dependent

Iodine and ruthenium chemistry

– Modelling at the State of the Art Global trends are well reproduced No reason to change the strategy yet adopted for several years in that field

which consists in a continuous modelling improvement as a direct feed-back from on-going interpretation of new experiments

MCCI

– Basic relevance of the set of models and assumptions

– Need for model improvements on coolability aspects

ERMSAR 2012, Cologne, March 21-23, 2012 15

Feed-back from the code assessmenton code the development process

First step: at short term, the main benefit for SARNET-WP4 partners using ASTEC comes from the periodical release by IRSN and GRS of improved V2.0 versions (revisions or patches)

Last delivered revision : V2.0-rev2 in December 2011– Improvement of the condensation processes in swollen level volumes– Transfer of the COCOSYS model of dry aerosol re-suspension in containment– Improvements of iodine reactions (in particular Ag/I in the sump)– …

Next planned revision : V2.0-rev3 to be delivered end of 2012– Extension of the RCS gas chemistry kinetics to the Cs-I-O-H-B-Mo system– Improved model for iodine interaction with paints under irradiation– 1st models for corium coolability during MCCI (top cooling and bottom cooling) – …– Moreover, besides new models, improvements are also expected from the

continuous interpretation of the experimental programmes underway or planned in SARNET2, ISTP, OECD or in French frame

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Towards future ASTEC V2 versions

Second step (medium term): Development of the next generation of ASTEC V2 versions New models under a new code structure

According to the V2.0-rev1 assessment, main ASTEC modelling efforts shall be spent in priority on the following open modelling issues:

– In-vessel SA phase Reflooding of severely degraded cores

RCS

gas chemistry kinetics– Ex-vessel SA phase MCCI, pool-scrubbing and DCH

Moreover, besides new physical models or improvements of existing ones, significant evolutions of the general code structure (and in particular of the core degradation module and its coupling to other ASTEC modules) have been identified few years ago at IRSN as a mandatory step to remove some current V2.0 limitations for plant analyses

To answer these requirements, the preparation of the future V2.1 version (future ASTEC major version) has already started at IRSN and GRS

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ASTEC V2.1 main features

End 2013: ASTEC V2.1 version– Integrating most of the SARNET2 knowledge– New CESAR/ICARE coupling (unique t/h in the whole RCS, no more switch after front

end phase), including also a 2D extension of the in-core thermal-hydraulics– Full capabilities for shutdown states and air ingress situations after vessel failure

(complete Ru behaviour also in RCS and advanced models for fuel oxidation under air atmosphere) and improved capabilities for vessel external cooling

– First version of a mechanistic model for reflooding of degraded cores– Extended RCS gas chemistry kinetics (according to available data)– Transfer of the COCOSYS model of DCH– Generalisation of the MDB use (centralized material database) to any ASTEC module– Integrating specific core models for BWR (canisters, sub-channels, …) and CANDU

First version applicable to the major part of Fukushima-Daiichi NPP accidents First version really applicable to spent fuel pool accidents

– Progress towards a “diagnosis” version Interfacing with atmospheric dispersion tools to enhance capabilities of direct comparison with

on-site measurement

– …

ERMSAR 2012, Cologne, March 21-23, 2012 18

Conclusion and perspectives

ASTEC V2 : a reference tool for Gen.II / Gen.III safety analyses

– ASTEC is and will remain a repository of the knowledge gained from international R§D, while progressively integrating the feed-back from the interpretations of Fukushima-Daiichi NPP accidents

– Axes for future ASTEC modelling improvements beyond V2.1 version are fully consistent with the recently updated SARP ranking

See ERMSAR-2012 paper on severe accidents research priorities

Other long-term objectives– Following-up the ASTEC extension to other reactors

Gen.IV SFR, ITER, …

– Progress towards a severe accident simulator

ERMSAR 2012, Cologne, March 21-23, 2012 19

Appendices

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ASTEC nodalisation for MISTRA MASP1and PANDA Test-18 simulations

MISTRA MASP1 PANDA test n°18

0

1

2

4

3

5

6

7

N3

N1

N4

N5

N6

N7

N8

N9

N10

N2

0 R1 R2 R3 R4 R5

R4Z060R2Z060 R0Z060

R4Z110 R2Z110 R0Z110

R4Z158R2Z158 R0Z158

R5Z158

R4Z205R2Z205 R0Z205

R5Z205

R4Z260R2Z260 R0Z260

R5Z260

R4Z363R2Z363 R0Z363

R5Z363

R4Z314R2Z314 R0Z314

R5Z314

R4Z413R2Z413 R0Z413

R5Z413

R4Z463R2Z463 R0Z463

R5Z463

R4Z513R2Z513 R0Z513

R5Z513

R4Z563R2Z563 R0Z563

R5Z563

R4Z613R2Z613 R0Z613

R5Z613

R4Z663R2Z663 R0Z663

R5Z663

R4Z713R2Z713 R0Z713

R5Z713

1,285

3,472

3,592

5,376

5,496

7,280

2,12*1,90

1,73 0,71

0,10

0,85

1,35

1,80

2,30

2,90

3,38

3,88

4,38

4,88

5,38

5,88

6,38

6,88

7,38

zones

R0* zones

R5* zones

R4* zones

R2* zones

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Sketch of the BMC facility

ERMSAR 2012, Cologne, March 21-23, 2012 22

According to the interpretations with ASTEC of CCI and VULCANO tests with siliceous concrete (CCI-3, CCI5, VULCANO VB-U5), main recommendations for MCCI full scale analyses are :

The use of Bali correlation for convective heat transfer coefficient seems to be appropriate;

The recommended value for the parameter (Tsol/Tliq interpolation parameter to evaluate the solidification temperature) must range within 0.3 – 0.4;

The proper value for the fraction of radiative power towards concrete above the corium seems to be in the range 0.0 – 0.2;

The slag heat transfer coefficient should be angular dependent. Recommended bottom/lateral values are 100.-200./1000 W/m2K;

The recommended value of layer volume swelling factor is 1.2

Set of best-estimate MCCI parameters for plant analyses