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For validation of structural integrity under normal and hypothetical accident conditions during transport and storage of radioactive material the Federal Institute for Materials Research and Testing (BAM) focuses its safety related scientific research on advanced mechanical safety assessment methods including simulation of high rate impact of model components and structures. A drop and crash test facility with an unyielding target and a load capacity of 1.200 kg was designed for materials testing of component size specimen under impact conditions at elevated and higher loading rates. The maximum drop height is 12 meters which enables impact velocities up to 15 m/s. An exactly falling test object or drop weight allows impact, bending, compression as well as crash and crush tests with maximum input energy of 118 kJ. An arresting unit has been developed to avoid multiple impacts during instrumented drop tests. The paper presents experimental techniques and examples of various measurement methods and advancements in order to assess assumption of materials and components behavior by definite displacement and stresses within mechanical testing. Instrumented drop weight tests are performed to complete materials data base and energy absorption of shock-absorbing materials and structures as well as to implement materials and structural parameters into FEA of reference structures. Furthermore, fracture mechanics parameters of thick walled DCI containers by means of dynamic bending tests are characterized by crack initiation and crack resistance behavior at the lowest operational temperature depending on the strain rate.
Finite element analysis (FEA) has been carried out for investigation of damping concrete under different impact loading conditions with a built-in material model and damage criteria available in FEA code ABAQUS.
At first, all parameters for the selected material model had been derived from compression Tests of cubic specimens. After that, a validation was carried out with different static and dynamic penetration tests. Finally, a 5 meter real drop test with a 23 Mg cylindrical cask could successfully be simulated.
Zur numerischen Simulation von Transport- und Lagerbehältern für radioaktive Stoffe unter mechanischen Unfallbedingungen sind geeignete
Materialmodelle und zugehörige Parametersätze für alle relevanten Behälterbauteile und den Aufpralluntergrund sowie gegebenenfalls für weitere am Störfall beteiligte Komponenten erforderlich.
Sie bilden eine wesentliche Grundlage um für unterschiedliche Belastungsvarianten und Temperaturen zuverlässige Berechnungsergebnisse zu ermitteln, die umfangreiche experimentelle Erprobungen zumindest in Teilen ersetzen und damit einen zentralen Bestandteil von sicherheitstechnischen Nachweisen in gefahrgut- und atomrechtlichen Zulassungs- und Genehmigungsverfahren bilden können. Für die Auslegung der Behälter von besonderer Bedeutung ist die Effizienz der eingesetzten energieabsorbierenden Elemente, wie beispielsweise Stoßdämpfer am Behälterdeckel oder -boden bzw. äquivalente Strukturen auf oder im Fundament von Zwischen- und Endlagern.
Diese Bauteile, die häufig aus Holz, Polyurethan (PU) - Schaum oder Dämpferbeton hergestellt werden, erfahren beim Auf- oder Anprall erhebliche plastische Deformationen, deren Verteilung und Größenordnung u.a. von der Belastungsgeschwindigkeit, dem Belastungsverlauf und der Temperatur bestimmt werden. Die Berücksichtigung dieser Faktoren in dynamischen Finite Elemente (FE) Berechnungen, die den heutigen Stand der Simulationstechnik repräsentieren, setzt eine systematische Datenbasis für den stoßdämpfenden Werkstoff voraus und die Implementierung dieser Informationen in numerischen Materialformulierungen.
An der BAM wird seit Ende 2008 im Rahmen des vom BMBF geförderten Forschungsvorhabens ENREA (Entwicklung rechnerischer Analysemethoden für stoßdämpfende Strukturen beim Anprall oder Absturz von Abfallgebinden) die experimentelle Bestimmung derartiger Daten sowie die Anpassung und teilweise Neuentwicklung geeigneter Materialmodelle betrieben.
The numerical Simulation of transport and storage casks for radioactive waste in accidental scenarios requires adequate material models and input parameters for all relevant structural cask elements, the Impact foundation as well as possibly further components involved in the incident. They form the basis for reliable analysis of different loading situations allowing substituting, at least in parts, experimental investigations that are needed in safety Reports submitted for nuclear licensing procedures.
Hereby, the efficiency of the energy absorbing components, such as cask Impact limiters or equivalent structures placed onto or into the foundation of storage buildings, determine to a large extend
the performance and thus the design of the casks. The limiters, which are usually made of wood, polyurethane foam (PUF) or damping concrete, are subjected to Major plastic deformations, whose Distribution and magnitude strongly depend on loading speed, course and temperature.
Consequently, it is necessary to establish a systematic data basis and implement this information in advanced numerical material formulations in Order to enable finite element simulations to account for all relevant factors.
Mechanical loading conditions of transport and storage casks for radioactive materials in accidental scenarios are highly affected by the behavior of both: the impact limiters and the footing materials. To minimize potential damages during the handling of casks, a so called damping concrete is frequently used for the footings in interim nuclear facilities. It obtains its shock absorbing properties through admixing of polymer cells. For a comprehensive mechanical evaluation of casks, advanced material models are also needed for damping concrete. In order to characterize the mechanical properties and to develop numerical material models, penetration tests were carried out at different test facilities of BAM. The tests contain static and dynamic penetration tests on cubic specimen with an edge length of 100 mm as well as mortared specimen with a size of 240 x 240 x 50 cm³. Indenters with different geometries and diameters were used for these model-sized penetration tests. Subsequently a full-scale cylindrical cast-iron indenter with a diameter of 110 cm was dropped of 5 m height on a realistic damping concrete footing.
The safety and integrity of casks for radioactive waste in accidental scenarios is analysed by BAM Federal institute tor Materials Research and Testing. An accidental scenario in German interim storage facilities is the drop from a crane during the handling operation. To reduce the mechanical loads to the cask a shock absorbing footing with high energy absorption capability is used in these areas. In order to analyse and evaluate such impact scenarios of casks, numerical simulations are performed. For a comprehensive simulation of an accidental scenario the behaviour of the damping concrete footing has to be taken into account as well and therefor a material model is needed. Material parameters under different loading conditions are the basis for a numerical model. For that reason a government funded research project (Kasparek, 2012) was conducted to characterise damping concrete under quasi-static as well as highly dynamic impact loading conditions. The performed tests include compression tests with and without lateral constraint small-scale and midscale penetration tests with different indenters, and finally a full-scale drop test onto a damping concrete footing.
Polyurethane foam used as impact limiter material undergoes high plastic deformations, whereat the resulting stress-strain relations strongly depend on loading speed and temperature. This paper discusses the efforts necessary to develop a reliable numerical foam simulation model focussing on generation and implementation of temperature- dependent yield curves
Ermittlung dynamischer Kennwerte von Dämpferbeton für die Simulation des Beanspruchungsverhaltens
(2016)
Die Sicherheit und Integrität von Verpackungen radioaktiver Stoffe wird anhand von numerischen Berechnungen bewertet. Bei einem Anprall oder Absturz sind die mechanischen Beanspruchungen auf die Behälter auch von den Eigenschaften des Untergrunds abhängig. Um potentielle Gefahren während der Verladung zu minimieren, wird energieabsorbierender Dämpferbeton in den Handhabungsbereichen nuklearer Lager eingesetzt.
Zu einer umfassenden sicherheitstechnischen Analyse und Bewertung gehört die Berücksichtigung des Beanspruchungsverhaltens von Dämpferbeton. Hierfür ist ein numerisches Materialmodell notwendig, das in der Literatur bisher nicht vorlag. Die dafür notwendigen dynamischen Kennwerte sind in verschiedenen Druck- und Eindringversuchen ermittelt worden. Dazu wurden dynamische Druckversuche an würfelförmigen Prüfkörpern durchgeführt, sowie Eindringversuche mit unterschiedlichen Eindringkörpern und Dämpferbetonproben. Die experimentell ermittelten Kennwerte wurden verwendet, um ein Materialmodell für Dämpferbeton zu entwickeln und kritische Beanspruchungsszenarien numerisch zu berechnen. Um die Qualität des Materialmodells zu überprüfen, wurde ein realitätsnaher Fallversuch eines Behälters in Originalgröße auf ein lagertypisches Dämpferbetonfundament durchgeführt.
In dem Beitrag sollen die unterschiedlichen Untersuchungen zur Ermittlung dynamischer Kennwerte sowie deren Ergebnisse dargestellt werden. Gezeigt werden ebenso numerische Nachberechnungen einzelner Versuche sowie die ausführliche Berechnung des Fallversuchs im Originalmaßstab. Experimentelle und numerische Ergebnisse aus der Simulation werden hier gegenübergestellt.
The shock absorbing material damping concrete is for the foundation in dry interim storage facilities for radioactive waste in Germany. In case of a potential cask drop damping concrete minimizes the mechanical loads to the cask. In course of safety analyzes this accident scenario is considered by numerical simulations using the finite element method. To get reliable results of numerical simulations a suitable material model is needed to take the characteristics of damping concrete into account. Due to the lack of sufficient material knowledge a research project was started to characterize the material’s behavior under different load conditions. This paper presents the test program to analyze the material behavior of damping concrete which is characterized by large volume change and
strain rate hardening dependence. The determined Parameters were used to adapt an existing material model of the FE-code ABAQUS®. This model has to handle the mechanical damage behavior of damping concrete which occurs under compression and shear loads during a potential cask drop. To verify the material model numerical simulations are compared with dynamic penetration tests, which were conducted with specimens assembled similar to the real application of the damping concrete footings. The transferability of the material
model to a real accident scenario was verified by a drop test with a full-scale cask on a damping concrete footing.
The shock absorbing material damping concrete is for the foundation in dry interim storage facilities for radioactive waste in Germany. In case of a potential cask drop damping concrete minimizes the mechanical loads to the cask. In course of safety analyzes this accident scenario is considered by numerical simulations using the finite element method. To get reliable results of numerical simulations a suitable material model is needed to take the characteristics of damping concrete into account. Due to the lack of sufficient material knowledge a research project was started to characterize the material’s behavior under different load conditions. This paper presents the test program to analyze the material behavior of damping concrete which is characterized by large volume change and
strain rate hardening dependence. The determined Parameters were used to adapt an existing material model of the FE-code ABAQUS®. This model has to handle the mechanical damage behavior of damping concrete which occurs under compression and shear loads during a potential cask drop. To verify the material model numerical simulations are compared with dynamic penetration tests, which were conducted with specimens assembled similar to the real application of the damping concrete footings. The transferability of the material
model to a real accident scenario was verified by a drop test with a full-scale cask on a damping concrete footing.