Long term performance of metal seals for transport and storage casks

Dual purpose casks for the transportation and storage of spent nuclear fuel and other radioactive materials require very high leak tightness of lid closure systems under accident conditions as well as in the long term to prevent activity release. For that purpose metal seals of specific types with an inner helical spring and outer metal liners are widely used and have shown their excellent performance if certain quality assurance requirements for fabrication and assembling are satisfied. Well defined surface roughness, clean and dry inert conditions are therefore essential. No seal failure in a loaded cask happened under these conditions until today. Nevertheless, the considered and licensed operation period is limited and all safety assessments have been performed and approved for this period of time which is 40 years in Germany so far. However, in the meantime longer storage periods might be necessary for the future and therefore additional material data will be required. BAM is involved in the qualification and evaluation procedures of those seals from the early beginning. Because long term tests are always time consuming BAM has early decided to perform additional tests with specific test seal configurations to gain a better understanding of the long term behaviour with regard to seal pressure force, leakage rate and useable resilience which is safety relevant mainly in case of accidental mechanical loads inside a storage facility or during a subsequent transport. Main test parameters are the material of the outer seal jacket (silver or aluminium) and the temperature. This paper presents the BAM test program including an innovative test mock-up and most recent test results. Based on these data extrapolation models to extended time periods are discussed, and also future plans to continue tests and to investigate seal behaviour for additional test parameters are explained.     

Ultrahigh-pressure consolidation and deformation of tantalum carbide at ambient and high temperatures

The deformation mechanism of the ultrahigh-temperature ceramic, tantalum carbide (TaC), consolidated at room temperature at a very high hydrostatic pressure of 7.7 GPa is investigated using high-resolution transmission electron microscopy. The deformation behavior of TaC at room temperature is also compared with that consolidated at high temperature (1830 °C) at a similar pressure. TaC could be consolidated to a bulk structure (90% theoretical density) at room temperature. The deformation mechanisms operating at room temperature and 1830 °C are found to be significantly different. The room-temperature deformation is dominated by the short-range movement of dislocations in multiple orientations, along with nanotwinning, grain rotation, crystallite misorientation with low-angle grain boundary formation and lattice structure destruction at interfaces. In contrast, at high temperature, the strain is accommodated mostly by a single slip system, forming a parallel array of dislocations. The consolidation at room temperature occurs by heavy deformation with the support from short range diffusion, whereas the consolidation at high temperature is mostly diffusion dominated, indicating a classic sintering mechanism. The improved degree of consolidation with fewer defects results in significantly improved elastic modulus and hardness in the case of high-temperature consolidate.     

Specification of hardware for interval arithmetic

Interval arithmetic, as it is standardized by the IEEE working group P1788 can be implemented by using floating point arithmetic units with directed rounding modes. The easiest way to represent an interval is by its two bounds. Simple formulas for the arithmetic operations can be applied. Our goal is to perform interval operations as fast as their floating point counterparts. Hence, we provide at least two units per operation. We also specify the operation for reverse multiplication (Neumaier in Vienna proposal for interval standardization, 2008) which can be implemented with the division unit. In this paper we do not care about optimization. Our primary intention is to give an easily understandable specification of hardware for interval arithmetic.     

Implementation of an algorithm for general material behavior of steel taking interaction between plasticity and transformation‐induced plasticity into account

In this article a semi‐implicit algorithm (predictor–corrector approach) for incorporating the interaction between plasticity and transformation‐induced plasticity (TRIP) in steel is developed. Contrary to the usual elasto‐plasticity, the underlying model of material behavior of steel is far more complex. The interaction between plasticity and TRIP requires extensions of algorithms developed in Doghri (Int. J. Numer. Meth. Engng 1993; 36 :3915–3932) and in Mahnken (Commun. Numer. Meth. Engng 1999; 15 :745–754). A particular feature of the algorithm is that the inner iteration can be reduced to a single scalar equation. Numerical examples illustrate the algorithm's capabilities. Copyright © 2011 John Wiley & Sons, Ltd.     

Shape-Optimized Photoacoustic Cell: Numerical Consolidation and Experimental Confirmation

The signal of photoacoustic sensors depends considerably on the shape of the sample cell. Taking advantage of acoustical resonances results in a signal boost and enables highly sensitive analyzers with low detection limits. A numerical optimization of the cell geometry has been performed with the objective being maximization of the photoacoustic signal. The resulting shape consists of a thin central pipe with flaring ends to both sides and is called an ??hourglass cell.?? In this article, the stability of the results and the limitations of the model are investigated. Influences of the absorbing molecule concentration and of the matrix gas are numerically examined. The results predict a stable signal increase of 32% to 36% compared to the well-established H cell and, thus, consolidate the model. A dependence on the absorption coefficient is not observed. The influence of matrix gas parameters (density, compressibility, speed of sound, specific heat, etc.) is small. Furthermore, an hourglass cell was manufactured and its performance for the detection of nitric oxide was compared to an H cell. These investigations demonstrate enhancements factors of 13.3% for the signal, 14.7% for the resonance quality, and 14.8% for the signal-to-noise ratio and adequately confirm the simulations.     

Groups of services delivered by Brazilian branchless banking and respective network integration models

Over the last decade, Brazil has pioneered an innovative model of branchless banking, known as correspondent banking, involving distribution partnership between banks, several kinds of retailers and a variety of other participants, which have allowed an unprecedented growth in bank outreach and became a reference worldwide. However, despite the extensive number of studies recently developed focusing on Brazilian branchless banking, there exists a clear research gap in the literature. It is still necessary to identify the different business configurations involving network integration through which the branchless banking channel can be structured, as well as the way they relate to the range of bank services delivered. Given this gap, our objective is to investigate the relationship between network integration models and services delivered through the branchless banking channel. Based on twenty interviews with managers involved with the correspondent banking business and data collected on almost 300 correspondent locations, our research is developed in two steps. First, we created a qualitative taxonomy through which we identified three classes of network integration models. Second, we performed a cluster analysis to explain the groups of financial services that fit each model. By contextualizing correspondents’ network integration processes through the lens of transaction costs economics, our results suggest that the more suited to deliver social-oriented, “pro-poor” services the channel is, the more it is controlled by banks. This research offers contributions to managers and policy makers interested in understanding better how different correspondent banking configurations are related with specific portfolios of services. Researchers interested in the subject of branchless banking can also benefit from the taxonomy presented and the transaction costs analysis of this kind of banking channel, which has been adopted in a number of developing countries all over the world now.     

Procedure to determine the impact of the surface film resistance on the hygric properties of composite clay/fibre plasters

The experimental determination of dynamic mass transfer properties of porous materials such as eco-efficient clay plasters is greatly influenced by the convective conditions at the surface of the material during the test. The measurement of the intrinsic vapour permeability of highly porous materials has shown to present wide discrepancies when the surface film resistance is not known. Therefore, a proper assessment of the hygric properties of clay plasters requires the determination of such resistance to vapour flow. An adapted experimental procedure was used to determine intrinsic water vapour permeability taking into account the influence of the surface film resistance. The moisture buffering test was used to measure dynamic exchange behaviour. The results gave evidence on the thickness of the active layer in the material and the impact of surface resistance on the exchange behaviour. A 1D mass transfer model was used to verify the validity of corrected vapour permeability by the surface film resistance and discuss its nature and influence on dynamic results.     

x-y-Recording in transmission electron microscopy. A versatile and inexpensive interface to personal computers with application to stereology

An interface for IBM XT/AT-compatible computers is described which has been designed to read the actual specimen stage position of electron microscopes. The complete system consists of (i) optical incremental encoders attached to the x- and y-stage drivers of the microscope, (ii) two keypads for operator input, (iii) an interface card fitted to the bus of the personal computer, (iv) a standard configuration IBM XT (or compatible) personal computer optionally equipped with a (v) HP Graphic Language controllable colour plotter. The small size of the encoders and their connection to the stage drivers by simple ribbed belts allows an easy adaptation of the system to most electron microscopes. Operation of the interface card itself is supported by any high-level language available for personal computers. By the modular concept of these languages, the system can be customized to various applications, and no computer expertise is needed for actual operation. The present configuration offers an inexpensive attachment, which covers a wide range of applications from a simple notebook to high-resolution (200-nm) mapping of tissue. Since section coordinates can be processed in real-time, stereological estimations can be derived directly “on microscope”. This is exemplified by an application in which particle numbers were determined by the disector method.