SARNET benchmark on QUENCH-11. Final report

In den QUENCH-Versuchen wird der Wasserstoffquellterm bei der Einspeisung von Notkühlwasser in einen trockenen, überhitzten Reaktorkern eines Leichtwasserreaktors untersucht. Ferner wird in den Versuchen das Verhalten von überhitzten Brennelementen unter verschiedenen Flutbedingungen untersucht, eine Datenbasis zur Modellentwicklung und eine Weiterentwicklung von Rechenprogrammen zu Schweren Störfällen (engl. SFD – Severe Fuel Damage) erstellt. Der Ausdampf-Versuch QUENCH-11 wurde am 8. Dezember 2005 durchgeführt. Es war das zweite Experiment im Rahmen des EU-geförderten LACOMERA-Programms. Es sollte einen Kühlmittelpumpenausfall während eines Kühlmittelverluststörfalls (hier ein sog. Small Break LOCA) oder einer plötzlichen Stromabschaltung (eng. „station blackout“) mit einer späten Druckentlastung des Primärsystems simulieren. Verbunden mit dem Unfallszenario ist das Ausdampfen eines teilgefüllten Reaktorkerns bzw. des Versuchsbündels. Das Ziel war die Untersuchung des Bündelverhaltens während des Ausdampfens und des nachfolgenden Abschreckens mit reduzierter Wassereinspeiserate. Es war das erste Experiment, in dem der gesamte Unfallablauf von der Ausdampfphase bis zur verzögerten Flutung des Bündels bei einer geringen Wasser-Einspeiserate untersucht werden sollte. Das Ausmaß der Wechselwirkungen von Thermalhydraulik und Materialien war in dem Experiment ausgeprägter als in früheren QUENCH-Versuchen. Das Experiment wurde von INRNE Sofia (Bulgarische Akademie der Wissenschaften) vorgeschlagen und zusammen mit dem Forschungszentrum Karlsruhe definiert. Nach dem Experiment wurde entschieden, die QUENCH-11-Daten für ein Rechenprogramm-Benchmark, bei dem die Rechenergebnisse mit den experimentellen Daten verglichen werden, im Rahmen des Europäischen Exzellenz-Netzwerks SARNET anzubieten, um die Zuverlässigkeit der Rechnungen für die verschiedenen Phasen von Unfall bzw. Experiment zu überprüfen. Die eingesetzten SFD-Rechenprogramme waren ASTEC, ATHLET-CD, ICARE-CATHARE, MELCOR, RATEG/SVECHA, RELAP/SCDAPSIM, und SCDAP/RELAP5. Die Koordination für den Vergleich übernahm INRNE. Als Grundlage für den Vergleich dienten die zeitlichen Verläufe von Temperaturen, Wasserstofferzeugung und anderer wichtiger Daten. Außerdem wurden Axialprofile, in erster Linie die der Temperatur zum Zeitpunkt des Flutbeginns und des Endstadiums, d. h. bei der Testzeit von 7000 s, verglichen. Für die meisten Rechenergebnisse kann ein gemeinsamer Trendverlauf angegeben werden. Größere Unterschiede zeigen die Ergebnisse für die Wasserstofferzeugung und die zugehörige Oxidschichtdicke. Der Grad der Übereinstimmung zwischen Rechnung und Experiment wird von den Schwachstellen der Rechnung und des Experiments gleichermaßen mitbestimmt. SFD-Rechenprogramme sind zur Analyse von typischen Kernreaktorunfällen entwickelt worden. Einzelne Besonderheiten der experimentellen Anordnung integraler Experimente (wie auch QUENCH-11) sind bedingt durch das Vorhandensein von Dampfführungsrohr (Shroud) und Elektrodenmaterial für die elektrische Stabheizung nicht reaktortypisch und können daher nicht in der gewünschten Einzelheit im Rechenprogramm nachgebildet werden. Hinzu kommen Effekte durch den Anwender. Da jedoch die Bandbreite der wesentlichen Rechenergebnisse einschließlich der Wasserstofferzeugung nicht extrem groß ist, kann das Ergebnis des SFD-Rechenprogramm-Benchmarks insgesamt als positiv bewertet werden. Ein Vergleich mit anderen Experimenten zeigt einen weiteren Bedarf an Verbesserungen besonders im Hinblick auf die Oxidation stark zerstörter Bündelstrukturen während des Flutens. Zusätzlich erwies sich das Rechenprogramm-Benchmark für einige Programmanwender als wertvoll, um sich mit den physikalischen Problematiken und der Anwendung von großen SFD-Rechenprogrammen vertraut zu machen. Es dient dem Erfahrungsaustausch mit jüngeren Wissenschaftlern und Ingenieuren und der Aufrechterhaltung des Standards der nuklearen Sicherheit

Benchmark study on fuel bundle degradation in the phebus FPT3 test using the severe accident codes ATHLET-CD, ICARE2, and MELCOR

This paper presents the results of pretest calculations of the Phebus fission product release experiment FPT3. The test scenario with the appropriate initial and boundary conditions was provided by the Institut de Radioprotection et de Sûreté Nucléaire. For the analyses, three severe accident codes were used: ATHLET-CD, ICARE2, and MELCOR. The calculations were focused on the main phenomena occurring in the bundle, such as the thermal behavior, the hydrogen production mainly due to cladding oxidation, the massive degradation of spent fuel and the release of fission products and control rod and structure materials. Using the predefined boundary and initial conditions, relatively small deviations between the code results were obtained, which demonstrates that the dominant processes occurring during a severe accident in the core of pressurized water reactors can be adequately simulated. By applying these codes to a large spectrum of integral tests as well as to plant analyses, one will obtain reliable results on the fuel bundle behavior. However, the spread in the calculated oxidized boron carbide masses indicates that modeling efforts are still necessary in all the codes in this respect

A high-content screen for small-molecule regulators of epithelial cell-adhesion molecule (EpCAM) cleavage yields a robust inhibitor.

Epithelial cell-adhesion molecule (EpCAM) is a transmembrane protein that regulates cell cycle progression and differentiation and is overexpressed in many carcinomas. The EpCAM-induced mitogenic cascade is activated via regulated intramembrane proteolysis (RIP) of EpCAM by ADAM and -secretases, generating the signaling-active intracellular domain EpICD. Because of its expression pattern and molecular function, EpCAM is a valuable target in prognostic and therapeutic approaches for various carcinomas. So far, several immunotherapeutic strategies have targeted the extracellular domain of EpCAM. However, targeting the intracellular signaling cascade of EpCAM holds promise for specifically interfering with EpCAM’s proliferation-stimulating signaling cascade. Here, using a yellow fluorescence protein–tagged version of the C-terminal fragment of EpCAM, we established a high-content screening (HCS) of a small-molecule compound library (n 27,280) and characterized validated hits that target EpCAM signaling. In total, 128 potential inhibitors were initially identified, of which one compound with robust inhibitory effects on RIP of EpCAM was analyzed in greater detail. In summary, our study demonstrates that the development of an HCS for small-molecule inhibitors of the EpCAM signaling pathway is feasible. We propose that this approach may also be useful for identifying chemical compounds targeting other disorders involving membrane cleavage-dependent signaling pathways

Benchmark study on fuel bundle degradation in the phebus FPT2 test using state-of-the-art severe accident analysis codes

This paper presents the results of posttest calculations of thephebus FPT2 experiment. While the exercise concentrates mainly on code-to-code benchmarking, a comparison is also made with selected experimental results. The test scenario with the appropriate initial and boundary conditions was provided by the Institut de Radioprotection et de SÛreté Nucléaire. For the analyses, seven severe accident analysis codes were used: ASTEC, ATHLET-CD, MELCOR, ICARE2, ICARE/CATHARE, SCDAP/RELAP5, and RELAP/SCDAPSIM. The calculations focused on the following phenomena occurring in the FPT2 bundle: thermal behavior; hydrogen production, mainly due to cladding oxidation; severe degradation of irradiated fuel; and the release of fission products, control rod, and structure materials. Using the same postdefined boundary and initial conditions, the code-data differences are typically within 10% for most parameters, and not more than 25%. More importantly, the codes were able to capture the major features of the transient evolution. Given that Phebus FPT2 exhibited almost all of the major low-pressure severe accident phenomena except for core cooling by water injection and late-phase core melt behavior in the lower head, the results engender a degree of confidence in the code predictive capability for sequences similar toFPT2

Analyses of the phébus FPT3 experiment using the severe accident codes ATHLET-CD, ICARE/CATHARE, and MELCOR

The aim of the Phébus Fission Product (FP) experimental program is to study the degradation phenomena and the behavior of the FPs released in the reactor coolant system and the containment building. The program consists of four in-pile bundle tests (FPTO, FPT1, FPT2, and FPT3), performed under different conditions concerning the thermal hydraulics and the environment of fuel rods, in particular, the amount of steam (strongly or weakly oxidizing atmosphere). The last test of this program, FPT3, was performed in November 2004 in Cadarache. During the FPT3 experiment, for the first time, boron carbide (B4C) was used as the absorber material instead of Ag-In-Cd, which was used in all the previous tests. Boron carbide is used in western-type pressurized water reactors, the EPR, boiling water reactors, and the WER; consequently, assessing the effects Of B4C on the main degradation phenomena and on gas release, as well as its impact on FP behavior is very important. This paper describes results from the Phébus FPT3 experiment, summarizes the test code modeling used in the different code applications, and reports the code results comparing some important experimental parameters, in particular regarding B4C control rod behavior. The severe accident codes used in these studies are Analysis of Thermal-Hydraulics of LEaks and Transients with Core Degradation (ATHLETCD), ICARE/CATHARE, and MELCOR. The first part is an overview of the experimental results (boundary conditions, temperature evolutions, hydrogen and carbon compound releases coming from the oxidation of the Zircaloy claddings and the B4C absorber, and bundle degradation). The second part summarizes the code modeling used in the different code applications, in particular, those regarding absorber rod degradation and the oxidation process. The third part summarizes the code results comparing some important experimental parameters [thermal behavior, gas releases (H 2, CO, CO2), and bundle degradation]. The conclusion focuses on the capabilities of the severe accident codes to simulate control rod behavior in a fuel rod assembly during the course of a severe accident transient

PHEBUS-FPTO Benchmark Calculations

Abstract not availableNA-NOT AVAILABL

B4C oxidation modelling in severe accident codes: Applications to PHEBUS and QUENCH experiments

Boron carbide is used in many nuclear power plants like BWR, VVER, some PWR, and EPR as a neutron absorber material. Consequently, it is important to assess its role in the core degradation phenomena during a severe accident (SA), as well as that of the carbon gas released from its degradation on the fission products behaviour. This paper describes the progresses achieved in the frame of the Network of Excellence SARNET concerning the B4C control rod degradation modelling in Severe Accident codes, such as ATHLET-CD, ICARE2, ASTEC MELCOR and MAAP. These new developments complete improvements made during the European Union 5th Framework COLOSS project. Starting from basic modelling derived from available tests reported in the literature, large improvements of the kinetic correlation for B4C oxidation were obtained from analytical experiments performed at FzK (Germany) and IRSN (France), mostly in the temperature range above 1400 K. The new modelling was considered in the analysis of experiments involving a B4C control rod in small fuel rod assemblies, such as Phebus FPT3 in-pile experiment, as well as out of pile experiments Quench 07 and 09, aimed at studying the course of severe accidents. Regarding the hydrogen generation, the results given by different code simulations are consistent with the experimental values. Concerning the control rod degradation, SA codes such as ICARE2 and ATHLET-CD, using suitable modelling of B4C oxidation, predicted rather well the total carbon release. The results of the MELCOR code, involving initially a B4C oxidation model designed to be used for BWR control blades, have been largely improved in the most recently released version, with a model extended for PWR B4C control rods. Codes still have some difficulties to reproduce the final degradation of fuel bundles involving B4C rods. Spreading of molten materials from the control rods onto fuel rods of the bundle is suspected, suggesting that the main effect of the B4C control rod materials on the bundle behaviour during degradation is connected with B4C-Stainless Steel (SS) eutectics formation and B4C-SS-Zry liquid mixture relocation. These phenomena are not accounted for in the SA codes. The need for further code developments of the early phase of core degradation is recognized, involving the absorber rod material behaviour. The BECARRE experiments, on-going in the framework of the International Source Term Program, are designed to provide in-depth understanding of these phenomena and help improving their modelling. © 2009 Elsevier Ltd. All rights reserved

Understanding the behaviour of absorber elements in silver-indium-cadmium control rods during PWR severe accident sequences

In the case of a hypothetical severe accident in a Pressurized Water Reactor (PWR), Silver-Indium-Cadmium (SIC) control rod failure occurs early during the sequence. Release of absorber melt could induce early fuel rod degradation by interaction of molten SIC alloy with fuel rod cladding, and the absorber materials could interact with the fission products, affecting significantly their speciation and transport in the primary circuit as well as their behaviour in the containment. This paper summarises the experimental and modelling progress made on this topic within SARNET over the whole project. Following a review of the status of knowledge, including the modelling in the main severe accident codes (ATHLET-CD, MAAP4, SCDAP, MELCOR, ASTEC), detailed calculations of the specific EMAIC and integral PHEBUS FPT2 experiments were performed. Accurate calculation of vapour pressure of the molten absorber elements is needed, requiring reliable values of the activity coefficients. The importance of accurate reproduction of the control rod degradation was shown, with the behaviour of absorber elements at rupture being critical as well as the thermodynamic data and speciation of the system Ag-In-Cd-Zr-H-O. The QUENCH-13 bundle experiment (FZK), conducted with a realistic integral geometry composed of 20 electrical heated rod simulators and one central SIC absorber rod, has helped to characterize the behaviour of absorber elements at the time of rod rupture, with measurements of the SIC release, using impactors (AEKI) and electrical low-pressure impactor and Berner low-pressure impactors (PSI). Coordinated pre and post-test calculations using SCDAP/RELAP5 based codes (PSI), MAAP4 (EDF), ATHLET-CD (GRS), ASTEC (IRSN) helped in defining the test and in its interpretation. Before this experiment, five tests were performed on small-scale SIC control rod samples using different designs and conditions. They helped in defining the conditions for the QUENCH-13 experiment. Five additional tests on similar small-scale samples are foreseen to help interpretation of the QUENCH-13 results. In QUENCH-13 the on-line aerosol measurements with electrical low-pressure impactors indicated control rod failure in the range 1550-1600 K; the test was terminated later at 1813 K by water reflood. Analysis of aerosols measured at sample points in the off-gas line showed significant Cd and In transport after rod failure with a smaller amount of transported Ag. Relocated SIC melt in the form of rivulets was detected in the lower part of the bundle. Investigation of SIC material properties (solidus, liquidus) by further analysis of data from QUENCH-13 is also presented. In parallel, an exhaustive review of activity coefficients of the elements in the SIC melt, including the effect of Zr was began (IRSN with the CNRS Marseille). © 2009 Elsevier Ltd. All rights reserved