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Organisationseinheit der BAM
Germany had been transporting spent fuel to the reprocessing plant in Sellafield and La Hague for decades until around 2005. Resulting from the obligation to take back the vitrified high-level waste from reprocessing six CASTOR® HAW28M filled with 168 canisters with radioactive waste in vitrified form were transported from Sellafield to the interim storage facility Biblis in 2020. Rail wagons were used for the transport to the port in Barrow-in-Furness, where they were loaded into a dedicated seagoing vessel, certified as INF Class 3 according to the INF Code. This was the first time that vitrified high level waste with considerable heat load was transported under a German design approval certificate.
BAM was involved in the authority assessment of the conditions for the sea transport. For the first transport BAM required among others, assessment of temperature distribution during transport, logging of temperatures of cargo bays and graphical imaging of temperatures of the bay with the cask in order to ensure compliance with temperature specifications, e.g. maximal neutron absorber and gasket temperatures. Special interest was taken in the identification of possible events exceeding the specified temperatures considering the different philosophies of IMDG code and its supplement INF code regarding temperature control of hatches. Results show compliance with assumed conditions.
Federal Institute for Materials Research and Testing (BAM) is the responsible authority for the
assessment of mechanical and thermal safety as well as quality issues within the licensing procedure
for transport casks for radioactive materials. The assessment includes a brittle fracture analysis of all
relevant cask components.
For cask bodies where a steel bottom is welded to a steel shell, specimens for testing of sufficient
fracture resistance can normally not be extracted directly from the welding seam area of the cask.
Therefore, a methodology has to be developed to ensure compliance with the safety analysis
considerations and the approved design specification. This paper describes such a methodology
including brittle fracture analysis and de-termination of required material properties as well as aspects
of quality assurance during manufacturing.
BAM Federal Institute for Materials Research and Testing is the competent authority for mechanical safety assessment of transport packages for radioactive material in Germany. The further development of state-of-the-art technology concerning assessment methods is essential for a qualified work of involved designers and authority experts. The paper gives an example of current development done to improve understanding and modeling capabilities of wood filled impact limiter. In order to reduce the loads applied to the package containment, which result from regulatory drop tests, most packages are protected by energy dissipating impact limiter. Wood, encapsulated by steel sheets, is one of the materials typically used for energy dissipation in these impact limiter. Very often, mechanical safety cases regarding the 9 m drop test are performed computationally, where it is essential to use reliable and verified computational methods and models. In this context, the paper presents an approach for a finite element material model for wood. Thereby, the mechanical behavior of wood under compression loading is the focus of the development work. Additionally, material orientation as well as strain rate, temperature and lateral constraint may vary. A large number of experiments, particularly compression tests, was designed and performed to establish an adequate experimental database for modeling verification. The experimental results enabled the derivation of necessary requirements: The material model has to take into account strain rate and temperature dependencies as well as the anisotropic characteristics of the material, a proper yield criterion, flow rule and hardening law. Such a material model is currently not available in established commercial dynamic finite element codes. Thus it is necessary to create a user-defined material model considering the mentioned requirements. A first step was done by determining a yield surface as well as detecting flow and hardening mechanisms from experimental force-deflection curves. In a next step the LS-DYNA material model MAT_75 was altered according to conclusions of former BAM development work, regarding the modeling of post-peak softening as a function of lateral constraint. Future research will contain the further development, implementation and verification of a material model for wood.
The moisture content of wood is known to have a significant influence on the woods mechanical properties. Using wood as an energy absorber in impact limiter of packages for the transport of radioactive material, it is of particu-lar importance to ensure the moisture content and thus relevant mechanical properties to be in specified limits. The paper surveys the influence of wood moisture content on the mechanical properties of wood. Different measuring methods are discussed with respect to in-situ applicability, accuracy and effort. The results of an experimental ana-lysis of the accuracy of hand-held moisture meters using the electrical resistance method are discussed. Conclu-sions are drawn regarding the measurement of moisture content of wood upon delivery as well as of complete im-pact limiter assemblies. Requirements for quality surveillance during manufacturing of wood filled impact limiter are derived and it is exemplified how to meet them. Construction, manufacturing and inspection of impact limiter encapsulation with regard to leak-tightness are addressed.
Using Scale Model Impact Limiter in the Type Assessment of Transport Casks for Radioactive Material
(2007)
Simulation of the Crushing of Wood Filled Impact Limiters for Packages of Radioactive Material
(2008)
Mechanical and thermal safety assessment of packages for transport of radioactive material in Germany is carried out by the Federal Institute for Materials Research and Testing (BAM). Both experimental and computational (analytical, numerical) methods combined with material and/or component tests are the basis for the state of the art safety assessment concept at BAM. The required mechanical tests according to IAEA regulations include, among others, a 9-m-drop-test on an unyielding target. Impact limiting components, which are attached to the cask at both ends, limit forces applied on the cask body and lid system by absorbing a major part of the impact energy. In Germany, impact limiters of packages for transport of radioactive materials are typically of steel-wood-sandwich construction, combining a relatively stiff steel structure bolted to the cask body, outer steel plates and different types of wood. By crushing the wood-steel-sandwich-structure between an unyielding target and the cask, the kinetic energy of a 9-m-free-fall is absorbed. The main energy absorber is wood under a high level of deformation. Wood under large deformations exhibits destruction of the fibre matrix. By analysing compression of the impact limiter wood after the drop tests with prototype casks for radioactive material, underlying mechanisms of wood crushing and corresponding energy absorption under large deformations are identified. Softening occuring at compression of the wood is a function of the lateral strain restriction of wood. Against the background of continuum mechanics an analogous model for compression of the fibre bundle is presented. The model takes the lateral strain restriction as triaxiality of the stress state into account. Further modelling possibilities for wood with a continuum approach are described. Different material laws in the explicit finite element code LS-DYNA are analysed for possible application using the analogous model for the fibre bundle. Small scale compression tests with wooden specimens are modelled in order to evaluate the ability of different modelling techniques to simulate softening. Although modelling of the compression of wood under large deformations is possible, softening could not be simulated purposefully. A drop test of a cask with impact limiting devices similar to existing impact limiters is simulated with different material laws for wood. The behaviour of impact limiting devices could not be simulated universally including the influence of the lateral strain restriction; nevertheless loading of the cask by crushing of the impact limiter could be simulated purposefully. Verification with experimental results is essential.