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  • VTT RESEA

    RCH N

    OTES 2311

    Molten Core Concrete Interactions in N

    uclear Accidents. Theory and D

    esign of an Experimental Facility

    Tt julkaisua myy Denna publikation sljs av This publication is available from

    VTT TIETOPALVELU VTT INFORMATIONSTJNST VTT INFORMATION SERVICEPL 2000 PB 2000 P.O.Box 2000

    02044 VTT 02044 VTT FI02044 VTT, FinlandPuh. 020 722 4404 Tel. 020 722 4404 Phone internat. + 358 20 722 4404Faksi 020 722 4374 Fax 020 722 4374 Fax + 358 20 7226 4374

    ISBN 951 38 6743 9 (soft back ed.) ISBN 951 38 6744 7 (URL: http://www.vtt.fi/inf/pdf/)ISSN 1235 0605 (soft back ed.) ISSN 1455 0865 (URL: http://www.vtt.fi/inf/pdf/)

    ESPOO 2005 VTT RESEARCH NOTES 2311

    In a hypothetical severe accident in a nuclear power plant, the molten coreof the reactor may flow onto the concrete floor of containment building.This would cause a molten core concrete interaction (MCCI), in which theheat transfer from the hot melt to the concrete would cause melting of theconcrete. In assessing the safety of nuclear reactors, it is important toknow the consequences of such an interaction.

    This publication includes a description of the basic theory of moltencore concrete interactions. A literature survey and some calculations ofthe physical properties of concrete and corium concrete mixtures at hightemperatures have been conducted. In addition, an equation is derivedfor conservative calculation of the maximum possible concrete ablationdepth. The publication also includes a literature survey of experimentalresearch on the subject of the MCCI and discussion of the results anddeficiencies of the experiments. The main result of this work is thegeneral design of an experimental facility to examine the interaction ofmolten metals and concrete.

    Tuomo Sevn

    Molten Core - Concrete Interactionsin Nuclear Accidents

    Theory and Design of an Experimental Facility

    Solid concrete

    Atmosphere

    Melt pool

    Gasbubbles

    Coriumcrust

    Moltenconcrete

    Solid concrete

    Atmosphere

    Melt pool

    Gasbubbles

    Coriumcrust

    Moltenconcrete

    http://www.vtt.fi/inf/pdf/http://www.vtt.fi/inf/pdf/

  • VTT TIEDOTTEITA RESEARCH NOTES 2311

    Molten Core Concrete Interactions in Nuclear

    Accidents Theory and Design of an Experimental

    Facility

    Tuomo Sevn VTT Processes

  • ISBN 9513867439 (soft back ed.) ISSN 12350605 (soft back ed.) ISBN 9513867447 (URL: http://www.vtt.fi/inf/pdf/) ISSN 14550865 (URL: http://www.vtt.fi/inf/pdf/) Copyright VTT 2005

    JULKAISIJA UTGIVARE PUBLISHER

    VTT, Vuorimiehentie 5, PL 2000, 02044 VTT puh. vaihde 020 722 111, faksi 020 722 4374

    VTT, Bergsmansvgen 5, PB 2000, 02044 VTT tel. vxel 020 722 111, fax 020 722 4374

    VTT Technical Research Centre of Finland, Vuorimiehentie 5, P.O.Box 2000, FI02044 VTT, Finland phone internat. +358 20 722 111, fax +358 20 722 4374

    VTT Prosessit, Lmpmiehenkuja 3 A, PL 1604, 02044 VTT puh. vaihde 020 722 111, faksi 020 722 5000

    VTT Processer, Vrmemansgrnden 3 A, PB 1604, 02044 VTT tel. vxel 020 722 111, fax 020 722 5000

    VTT Processes, Lmpmiehenkuja 3 A, P.O.Box 1604, FI02044 VTT, Finland phone internat. + 358 20 722 111, fax + 358 20 722 5000

    Technical editing Anni Kriinen Otamedia Oy, Espoo 2005

    http://www.vtt.fi/inf/pdf/http://www.vtt.fi/inf/pdf/

  • 3

    Sevn, Tuomo. Molten Core Concrete Interactions in Nuclear Accidents. Theory and Design of an Experimental Facility [Sydnsulan ja betonin vuorovaikutukset ydinvoimalaonnettomuuksissa: Teoriaa ja koelaitteiston suunnittelu]. Espoo 2005. VTT Tiedotteita Research Notes 2311. 83 p.

    Keywords nuclear power plants, nuclear safety, reactor core, meltdown, concrete structures, containment buildings, spalling, cracking, simulation, MELCOR

    Abstract In a hypothetical severe accident in a nuclear power plant, the molten core of the reactor may flow onto the concrete floor of containment building. This would cause a molten core concrete interaction (MCCI), in which the heat transfer from the hot melt to the concrete would cause melting of the concrete. In assessing the safety of nuclear reactors, it is important to know the consequences of such an interaction.

    As background to the subject, this publication includes a description of the core melt stabilization concept of the European Pressurized water Reactor (EPR), which is being built in Olkiluoto in Finland. The publication includes a description of the basic theory of the interaction and the process of spalling or cracking of concrete when it is heated rapidly. A literature survey and some calculations of the physical properties of concrete and coriumconcrete mixtures at high temperatures have been conducted. In addition, an equation is derived for conservative calculation of the maximum possible concrete ablation depth. The publication also includes a literature survey of experimental research on the subject of the MCCI and discussion of the results and deficiencies of the experiments.

    The main result of this work is the general design of an experimental facility to examine the interaction of molten metals and concrete. The main objective of the experiments is to assess the probability of spalling, or cracking, of concrete under pouring of molten material. A program of five experiments has been designed, and pre-test calculations of the experiments have been conducted with MELCOR 1.8.5 accident analysis program and conservative analytic calculations.

  • 4

    Sevn, Tuomo. Molten Core Concrete Interactions in Nuclear Accidents. Theory and Design of an Experimental Facility [Sydnsulan ja betonin vuorovaikutukset ydinvoimalaonnettomuuksissa: Teoriaa jakoelaitteiston suunnittelu]. Espoo 2005. VTT Tiedotteita Research Notes 2311. 83 s.

    Keywords nuclear power plants, nuclear safety, reactor core, meltdown, concrete structures,containment buildings, spalling, cracking, simulation, MELCOR

    Tiivistelm Vakavassa ydinvoimalaitosonnettomuudessa reaktorin sulanut sydn voi valua suojara-kennuksen betonilattialle. Tst voi seurata sydnsulabetoni-vuorovaikutus, jossa lm-p siirtyy kuumasta sulasta betoniin, mik aiheuttaa betonin sulamisen. Arvioitaessa ydinvoimaloiden turvallisuutta on trke tuntea tllaisen vuorovaikutuksen seuraukset.

    Tss tutkimuksessa aiheen taustaksi kuvataan Olkiluotoon rakennettavan EPR-paine-vesireaktorin sydmen sulamisonnettomuuden hallintakonsepti. Tutkimuksessa kerro-taan sydnsulabetoni-vuorovaikutuksen perusteista sek betonin nopean lmmittmi-sen aiheuttamasta spalling-ilmist eli lohkeilusta. Betonin ja coriumbetoni-seosten fysikaalisia ominaisuuksia korkeissa lmptiloissa selvitetn kirjallisuuden ja laskujen avulla. Lisksi johdetaan yhtl betonin suurimman mahdollisen sulamissyvyyden las-kemiseksi. Julkaisu sislt mys kirjallisuusselvityksen sydnsulabetoni-vuorovai-kutusten kokeellisesta tutkimuksesta sek pohdintaa kokeiden tuloksista ja puutteista.

    Tutkimuksen trkein tulos on yleissuunnitelma koelaitteistolle, jolla voidaan tutkia su-lan metallin ja betonin vuorovaikutusta. Kokeiden trkein tavoite on selvitt spalling-ilmin todennkisyytt, kun sulaa materiaalia kaadetaan betoniastiaan. Tutkimuksessa suunnitellaan viiden kokeen ohjelma ja kokeista on tehty laskelmia MELCOR 1.8.5 -onnettomuusanalyysiohjelmalla sek konservatiivisilla ksinlaskuilla.

  • 5

    Preface

    This text has been written as a masters thesis for the department of Engineering Physics and Mathematics at Helsinki University of Technology. Part of the funding was obtained from SAFIR, the Finnish research program on nuclear power plant safety. I am grateful to VTT Processes for the opportunity to write my masters thesis on this interesting subject. I want to thank especially my instructor, senior research scientist Ilona Lindholm, and supervisor, professor Rainer Salomaa for advice and comments about the work. Thanks go also to Heikki Sjvall from TVO and Risto Sairanen from STUK for providing information about the sacrificial concrete in the EPR reactor pit and for reviewing this thesis. And finally, thanks to my parents who have supported my studies.

    Otaniemi, 13 October 2005

    Tuomo Sevn

  • 6

    Contents

    Abstract..............................................................................................................................3

    Tiivistelm.........................................................................................................................4

    Preface ...............................................................................................................................5

    1. Introduction..................................................................................................................8

    2. EPR Core Melt Stabilization Concept .......................................................................10

    3. Theory of Molten Core Concrete Interactions ........................................................13 3.1 Phenomenology ................................................................................................13 3.2 Behavior of Concrete at High Temperatures....................................................15

    3.2.1 Composition and Physical Structure of Concrete ................................15 3.2.2 Temperature Effects on the Composition of Concrete.........................16 3.2.3 Spalling of Concrete.............................................................................17 3.2.4 Thermal Properties of Concrete at High Temperatures .......................19

    3.3 Heat Transfer from Molten Material to Concrete.............................................27 3.4 Conservative Estimation of the Ablation Depth.....................