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atw Vol. 65 (2020) | Issue 10 ı October RESEARCH AND INNOVATION 512 | Fig. 5. Correlation between the adjusted HEFF and the heating power for the axial and radial erosion of the BETA experiments with siliceous concrete without and with addition of zirconium in the melt. In the simulations with the initial modelling (Figure 3), the axial erosion in V2.1 is clearly underestimated, whereas in V1.6 – V1.8 it is over estimated. The erosion can be re presented well only in case of V1.5. In the experiments with higher heat output, in particular, the strong erosion rate at the beginning cannot be reproduced by the simulation. With increasing heating power, the difference in the early phase between experiment and simulation becomes more and more apparent. V1.8 stands out because neither the erosion depth nor the consistently high erosion speed can be simulated with the recommended values [SPE12]. The axial erosions of the adjusted simulations are shown in Figure 4. The adaption is only done on the effective heat transfer coefficients as previously explained, while the decomposition temperature and decomposition enthalpy stay constant. The variation of HEFF better simulates erosion in all experiments. The initial strong increase cannot be improved only by adjusting HEFF. However, the course of the erosion in the further experiment is reproduced much better. In order to be able to evaluate a possible connection between the heat input and adjusted HEFF, the two variables are plotted against each other shown in Figure 5. This connection is separated between the value of HEFF in the axial and radial directions. The radial values are significantly smaller than those for the axial direction due to the lower radial erosion. Using the drawn regression curves for the silicate concrete in Figure 5, the relationship between the heating power and the effective heat transfer coefficient can be better represented. It can be seen that a higher heat output results in a higher effective heat transfer coefficient. This relationship might be explained by an increased movement of the melt, which then leads to an improved heat transfer between melt and concrete. The higher velocity of the melt is, amongst other things, due to the greater erosion volume at higher heat output. Due to the larger erosion volume, a higher gas release, which additionally sets the melt in motion, can be assumed. The described effect has a greater influence on the axial direction, relative to the radial direction. In addition to the simulations with silicate concrete without additions in the melt, the variation was also carried out on the experiments with additionally added zirconium to the melt (V5.1 – V5.3). The corresponding values are also shown in Figure 5. They are higher than the values for the axial erosion in the simulations for silicate concrete without additives in the melt. Zir co nium causes an exothermic chemical oxidation reaction and introduces more energy into the melt, which can be equated with an additional heat input. This results in a higher erosion of the concrete, compared to the experiments without zirconium with the same heat input. The higher erosion, in turn, leads to an additional movement of the melt. Thereby the heat transfer from the melt to the concrete is improved. This improvement is reflected in an increased value for HEFF, as seen in Figure 5. The influence of zirconium in the melt shows a differentiated behaviour for radial erosion. In contrast to the adjusted parameter in the axial direction, it decreases in the radial direction compared to the base simulation. From this, as expected, it can be concluded that the heat output is not the only influencing parameter responsible for the heat transfer between melt and concrete. Conclusion The results for the erosion investigated here show that COCOSYS V3.0 is able to simulate the presented BETA experiments. It is possible to map erosion depths and gradients. Deviations can be recognized only at high heating power and the associated high erosion rates at the beginning of MCCI. For this effect, there is still potential for development. The investigations have also shown that the recommended modelling of a melt-concrete interaction, with constant heat transfer coefficients HEFF, between melt and concrete, at different heat outputs, is not optimal yet. Increasing heating power results in higher heat transfer coefficients. However, this is not solely dependent on the heating power, as the influence of zirconium in the melt has shown. In the adjusted simulations, HEFF increases in the axial direction with the addition of zirconium in the melt, whereas HEFF decreases in the radial direction. There must be other para meters that have an influence on the heat transfer between melt and concrete. These include the release of gas by the decomposition of the concrete, the crusting by the soli dification of the melt, as well as the temperature between the melt and the concrete. Specifically, the decompo sition temperature of the concrete is currently being investigated with the MOCKA experiments [FOI19]. First of all, the correlation between the effective heat coefficient and the heating power needs to be tested and described in more detail with in dependent experiments with similar concrete composition. The heat transfer coefficient is not constant during MCCI and it is recommended to develop a correlation Research and Innovation Simulation of Selected BETA Tests with the Severe Accident Analysis Code COCOSYS ı Maximilian Hoffmann and Marco K. Koch
atw Vol. 65 (2020) | Issue 10 ı October where the heat transfer is recalculated during the interaction, to consider the effect of a variable decay heat, for example. This requires further investigation in order to identify as many influencing parameters as possible and to incor porate them into the correlation. References [AGE18] K. Agethen, M. Hoffmann, M.K. Koch: Analyse und Bewertung der COCOSYS-Modellbasis zu Ex-Vessel Phänomenen während MCCI. Technischer Fachbericht zum Forschungsvorhaben BMWi 1501512, AG Plant Simulation and Safety, Ruhr-Universität Bochum, 2018, PSSTR3. [ALS86] H. Alsmeyer, C. Adelhelm, H.-G. Dillmann, J. Foit, M. Heinle, W. Ratajczak, H. Schneider, G. Schumacher, A. Skokan, S. Stiefel, W. Tromm; BETA experiments on melt-concrete interaction: the role of Zirconium and the potential sump water contact during melt-down accidents. Bd. 154. 61-68 No. 1. DOI: 10.1016/ 0029-5493(94)00898-9. – Nuclear Engineering und Design, 1986, S. 61–68. [ALS92] H. Alsmeyer: Proceedings of the Second OECD (NEA) CSNI Specialist Meeting on Molten Core Debris- Concrete Interactions, OECD Nuclear Energy Agency in collaboration with Kernforschungszentrum Karlsruhe, April 1992, NEA/CSNI/R(92)10. [ALS95] H. Alsmeyer, G. Cenerino, E. Cordfunke, D. Fioravanti, M. Fischer, J. Folt, L. Howe, M. Huntelaar, S. Locatelli, F. Parozzi, J. Szabo, B. Turland, M. Vidard, D. Wegener; Molten corium/concrete interaction and corium coolability - A state of the art report. (EUR16649), European Commision - Nuclear Science und Technology, 1995. [ALL07] H.-J. Allelein, S. Arndt, W. Klein-Heßling, K. Neu, N. Reinke, S. Schwarz, B. Schwinges, C. Spengler, G. Weber: Intensivierte Validierung der Rechenprogramme COCOSYS und ASTEC, Final Report, November 2007, GRS-A-3330. [CRA13] M. Cranga, C. Spengler, K. Atkhen, S. Bechta, P. Bottomley, P. Dejardin, A. Fargette, M. Fischer, J.J. Foit, R. Gencheva, P. Grudev, E. Guyez, J.F. Haquet, C. Journeau, G. Langrock, B. Michel, C. Mun, G. Ratel, T. Sevon, B. Spindler: State-of-the-Art-Report on MCCI in dry conditions: Analysis of experiments, modelling and reactor applications, IRSN, August 2013, PSN- RES/SAG/2013-00076. [FOI19] J.J. Foit, T. Cron, B. Fluhrer: Melt/Concrete Interface Temperature relevant to MCCI Process, Karlsruhe Institute of Technology (KIT), The 9 th European Review Meeting on Severe Accident Research (ERMSAR2019), March 2019 [PEE83] M. Peehs, R. Höpfl, B. Gather, R. Blachnik: Die integrale Schmelzeenthalpie von Reaktorbeton als thermophysikalische Eingangsgröße von Unfallfolgemoedellen des hypothetischen Kernschmelzeunfalls, Journal of Nuclear Materials 118 p. 206-213, 1983. [SPE12] C. Spengler, S. Arndt, J. Arndt, J. Bakalov, S. Band, J. Eckel, W. Klein-Hessling, H. Nowack, M. Pelzer, N. Reinke, J. Sievers, M. Sonnenkalb, G.Weber; Weiterentwicklung der Rechenprogramme COCOSYS and ASTEC – Abschlussbericht. (GRS – A – 3654), Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH, 2012. [SPE18] C. Spengler et al., “Uncertainty and Sensitivity Analyses in Support of Model Development and Validation of the Containment Module COCOSYS of the AC2 Code - Application for Molten Corium/ Conrete Interaction (MCCI),” in Proceedings of NUTHOS-12, Qingdao, China, 2018. Authors Maximilian Hoffmann maximilian.hoffmann@pss.rub.de Prof. Marco K. Koch Ruhr-Universität Bochum Plant Simulation and Safety Group Universitätsstraße 150 44801 Bochum, Germany Imprint Imprint Official Journal of Kerntechnische Gesellschaft e. V. (KTG) Publisher INFORUM Verlags- und Verwaltungsgesellschaft mbH Robert-Koch-Platz 4, 10115 Berlin, Germany Phone: +49 30 498555-33 www.nucmag.com General Manager Dr. Thomas Behringer Editor in Chief Christopher Weßelmann +49 2324 4397723 editorial@nucmag.com Managing Editor Nicolas Wendler +49 30 498555-21 nicolas.wendler@nucmag.com Editorial Advisory Board Frank Apel Erik Baumann Dr. Erwin Fischer Carsten George Eckehard Göring Dr. Florian Gremme Dr. Ralf Güldner Carsten Haferkamp Dr. Anton Kastenmüller Prof. Dr. Marco K. Koch Ulf Kutscher Herbert Lenz Jan-Christan Lewitz Andreas Loeb Dr. Thomas Mull Dr. Joachim Ohnemus Olaf Oldiges Dr. Tatiana Salnikova Dr. Andreas Schaffrath Dr. Jens Schröder Norbert Schröder Prof. Dr. Jörg Starflinger Dr. Brigitte Trolldenier Dr. Walter Tromm Dr. Hans-Georg Willschütz Dr. Hannes Wimmer Layout zi.zero Kommunikation Antje Zimmermann Berlin, Germany Printing inpuncto:asmuth druck + medien gmbh Buschstraße 81, 53113 Bonn, Germany Editor @atw_Journal @atw-international-journal-for-nuclear-power Nicole Koch +49 163 7772797 nicole.koch@nucmag.com Advertising and Subscription Petra Dinter-Tumtzak +49 30 498555-33 petra.dinter@nucmag.com Price List for Advertisement Valid as of 1 July 2020 Published 9 times a year (double issues: 6/7, 8/9, 11/12) Germany: Per issue/copy (incl. VAT, excl. postage) 23.55 € Annual subscription (incl. VAT and postage) 183.50 € All EU member states without VAT number: Per issue/copy (incl. VAT, excl. postage) 23.55 € Annual subscription (incl. VAT, excl. postage)183.50 € EU member states with VAT number and all other countries: Per issues/copy (no VAT, excl. postage) 22.43 € Annual subscription (no VAT, excl. postage) 174.77 € Copyright The journal and all papers and photos contained in it are protected by copyright. Any use made thereof outside the Copyright Act without the consent of the publisher, INFORUM Verlags- und Verwaltungsgesellschaft mbH, is prohibited. This applies to reproductions, translations, micro filming and the input and incorporation into electronic systems. The individual author is held responsible for the contents of the respective paper. Please address letters and manuscripts only to the Editorial Staff and not to individual persons of the association's staff. We do not assume any responsibility for unrequested contributions. Signed articles do not necessarily represent the views of the editorial. ISSN 1431-5254 RESEARCH AND INNOVATION 513
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