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Autor*in

  • Zencker, Uwe (115)
  • Völzke, Holger (43)
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  • Qiao, Linan (29)
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Organisationseinheit der BAM

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Relevance of cladding failure mechanisms due to zirconium hydride precipitation under extended dry storage conditions in Germany (2017)
Orellana Pérez, Teresa ; Völzke, Holger ; Wolff, Dietmar ; Zencker, Uwe Zencker
The German nuclear waste management strategy consists of dry interim storage of spent fuel inside dual purpose casks and its subsequent direct final disposal in a deep geological repository. Interim storage is limited to 40 years so far, but will have to be extended until repository site selection and operation is concluded, potentially up to 100 years. In this context, research on the long term performance of safety relevant cask components and fuel rod integrity during such extended periods of time is of outmost importance. The barrier function of the fuel cladding depends on its integrity under operational and accidental conditions along with storage and subsequent transportation and is mainly affected over time by altering of the cladding microstructure and by thermo-mechanical conditions during reactor operation and subsequent wet and dry storage. This paper focuses on failure mechanisms regarding cladding embrittlement caused by physical phenomena concerning hydrogen dissolution and precipitation of hydrides in the zirconium matrix. Within this context, potential cladding integrity issues under extended interim storage conditions followed by transportation are emphasized. Delayed hydride cracking (DHC) is a well-known time-dependent temperature-activated phenomenon failure mechanism of the fuel cladding during reactor operation. The phenomenon consists of hydrogen diffusion and hydride precipitation at the tip of an initial crack and the propagation of the crack to an approximate distance equal to the length of the hydride. This failure mechanism is temperature-activated phenomenon and enhances along with thermal cycling of the fuel cladding, e. g. during reactor shutdowns. DHC shows limited relevance under quasi static storage conditions with continuously lowering temperatures. However, the literature points that DHC may occur when the temperature during storage decreases to a certain level after some decades and in combination with stress concentrations in the cladding material. When spent fuel is transferred to dry storage by vacuum drying, the cladding temperature raises up to peak temperatures of ~370°C. Under these conditions, hydrides dissolute into the zirconium matrix up to the solubility limit defined by the peak temperature and this amount of hydrogen can precipitate in a radial re-oriented fashion due to the temperature decrease during storage. Cladding materials with radially precipitated hydrides show significant embrittlement. Radially oriented hydrides are perpendicularly oriented to hoop stresses representing the most critical configuration. Brittle failure of the cladding then occurs by crack propagation through radially oriented hydrides and finally through the zirconium matrix. The susceptibility to radial hydride precipitation depends on cladding material type and microstructure, hydrogen content, pre-drying hydride distribution, irradiation conditions, and temperature and stress histories during drying and storage operations. This paper addresses major considerations concerning spent fuel cladding embrittlement due to hydride precipitation with regard to the boundary conditions of dry spent fuel storage in Germany. Analytical, numerical, and experimental approaches are to be discussed by BAM in order to identify the specific needs for future R&D work in that area with the purpose to provide the necessary data base for proper safety demonstration and evaluation along with future extended storage licensing procedures.
Numerical analysis of cask accident scenarios in storage facilities (2014)
Weber, Mike ; Zencker, Uwe ; Wolff, Dietmar ; Völzke, Holger ; Herbrich, Uwe ; Nagelschmidt, Sven
Mechanical drop test scenarios for Type B (U) packages according to the IAEA regulations have to be carried out onto the so-called “unyielding target” (usually with cask impact limiters) and onto the puncture bar respectively. They are predefined and do not require any further investigation of scenarios that really could happen on transportation routes. Cask accident scenarios in the framework of approval procedures for interim storage sites are derived from a detailed analysis of the handling procedures necessary from arrival of cask at the site to its storing position. In that case, casks are usually handled without impact limiters. Dependent on possible drop heights, drop positions and floor properties, conservative cask accident scenarios are derived for further safety proofs. According to the mechanical assessment concept of the considered approval procedure numerical calculations have to be provided by the applicant to demonstrate mechanical cask safety. Stresses and strains in the cask body as well as in the lid System have to be identified and assessed. Using the example of a 3-mvertical-drop of a transport and storage cask for spent fuel elements onto the floor construction made of damping concrete covered by screed, BAM developed a finite element model. The finite element code ABAQUS/Explicit™ was used. Results of experimental investigations are not available. Therefore parameter studies are necessary to identify the sensitivity of the finite element model to significant Parameters and to verify the finite element models according to the requirements of the Guidelines for the Numerical Safety Analyses for the Approval of Transport and Storage Casks for Radioactive Materials (BAM GGR-008). The paper describes the modeling of the material behavior and attachment of bottom side cask components. Questions concerning the modeling of a crack length limiting reinforcement in the screed layer are discussed. The influence of the mesh density of the screed layer and its strength is considered as well. Finally, the developed finite element model can be used for a numerical safety assessment. It can help to understand the complex mechanisms of the interaction between the cask components and floor construction.
Numerical analysis of cask accident scenarios in storage facilities (2013)
Weber, Mike ; Zencker, Uwe ; Wolff, Dietmar ; Völzke, Holger ; Herbrich, Uwe ; Nagelschmidt, Sven
Existing spent nuclear fuel (SF) and high active waste (HAW) management policies and practices worldwide are the result of past presumptions that sufficient reprocessing and/or disposal capacity would be available in the near term. Consequently, in the past many countries have developed specific solutions for different periods of time due to their individual national nuclear policies. In Germany the concept of dry interim storage in dual purpose metal casks before disposal is being pursued for SF and HAW management and transport and storage licenses have been issued accordingly. The current operation licenses for existing storage facilities have been granted for a storage period of up to 40 years. This concept has demonstrated its suitability for over 20 years so far. Relevant safety requirements have been assessed for the short-term as well as for the long-term for site-specific operational and accidental storage conditions. But in the meantime significant delays in the national repository siting procedure occurred which will make extended storage periods necessary in the future.
Dynamic fracture mechanics assessments for cubic ductile cast iron containers (2000)
Zencker, Uwe ; Zeisler, Peter ; Droste, Bernhard
Strategien zur Bestimmung von Temperaturen von Transport- und Lagerbehältern für radioaktive Stoffe (2010)
Bletzer, Claus W. ; Zencker, Uwe ; Völzke, Holger ; Nehrig, Marko
Mechanical design assessment approaches of actual spent fuel and HLW transport package designs (2010)
Wille, Frank ; Droste, Bernhard ; Müller, Karsten ; Zencker, Uwe
Numerical and experimental studies of polyurethane foam under impact loading (2011)
Kasparek, Eva Maria ; Zencker, Uwe ; Scheidemann, Robert ; Völzke, Holger ; Müller, Karsten
Proper predictions of the behaviour of shock absorber materials are of utmost importance in safety assessments for licensing casks for transport and storage of highly active waste. After having identified significant discrepancies between numerical results and the actual response of polyurethane foam limiters subjected to accidental scenarios, a new research project ENREA was established by BAM. A major objective is to enhance and to develop advanced material models intended to simulate limiters under impact loading. They should account for all major factors influencing the load–deformation relationship like temperature, strain rate and specific stress state. The corresponding test program, applicable plasticity models, the overall parameter identification strategy based on local and global optimization techniques as well as experimental and numerical results are presented here in particular for closed cell foams.
Mechanical and thermal safety analyses and demonstrations for cubic DCI multipurpose containers (1997)
Völzke, Holger ; Wieser, Günter ; Zencker, Uwe ; Droste, Bernhard
Mechanical and thermal safety analyses and demonstrations for cubic DCI - multi-purpose containers (1997)
Völzke, Holger ; Wieser, Günter ; Zencker, Uwe ; Droste, Bernhard
Entwicklung von Beurteilungsmethoden für Transport- und Lagerbehälter mit erhöhten metallischen Reststoffanteilen (EBER) - FEM-Berechnungen zum Aufprall kubischer Gußcontainer (1997)
Zencker, Uwe ; Völzke, Holger ; Droste, Bernhard
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