PVP2006-ICPVT11-93393 FEM SIMULATION OF EXTREME THERMAL AND MECHANICAL ACCIDENT LOADS ON SCREWED SPENT FUEL CASK LID STRUCTURES

ABSTRACT The complex analysis of screwed spent fuel cask lid structures under extreme thermal and mechanical loads is very important for the evaluation of cask integrity and leak tightness under such conditions. The interest of such problems has been increasing since the terrorist attacks from September 11, 2001. Due to extension experiences of BAM in calculation and experimental testing of transport and storage casks for radioactive materials, BAM in this context has developed new methods to estimate the safety margins of transport and storage spent fuel and high-level waste casks under extreme thermal and mechanical loads resulting from aircraft crashes. In case of thermal loads, a thermal heat transfer analysis has to be made, which gives the time-dependent temperature distribution of the casks. But this is not enough, while the extreme kerosene fire scenario creates a strong transient heating of the cask body and its lid system. This causes elastic and plastic deformation of the cask body, the decrease of screw forces and especially great relative displacements between the seals and its contacting flanges. This results in an elevated leak rate. To cover this case so-called thermo-mechanical analyses had been carried out. One of the most critical mechanical loads on the cask is a central impact onto the lid-seal-system. This can be caused by direct aircraft crash or its engine as well as by a following impact of building structures of a nuclear facility like a storage hall. In this situation dynamical analyses had been carried out. Although it is currently not possible to calculate the leakage rates from deformation analysis directly, for the present it is possible to estimate the behaviour of the seal based on the calculated relative displacements at its place and the behaviour of the lid bolts under the thermal and mechanical impact loads respectively, in combination with experiments where the leakage rate of the seals had been measured after radial and axial shifting of the flanges. Except of the lid bolts, the geometry of the cask and the thermal/mechanical loads are axial-symmetric, which simplified the analysis considerably by using two dimensional finite element models and parameter studies are possible. The lid bolts had been "smeared" with a special technique as twodimensional plane-stress bolt model, which has been verified with three dimensional bolt calculations. Experiments and calculation studies show that the German transport and storage casks for radioactive material have sufficient safety margins even by extreme thermal/mechanical loads. This paper will present the methodologies developed for the studies. Some of the calculation results will be presented

Introduction of a Power Law Time-Temperature Equivalent Formulation for the Description of Thermorheologically Simple and Complex Behavior

In this work, a conceptual framework is suggested for analyzing thermorheologically simple and complex behavior by using just one approach. Therefore, the linear relation between master time and real time which is required in terms of the time-temperature superposition principle was enhanced to a nonlinear equivalent relation. Furthermore, we evaluate whether there is any relation among well-known existing time-temperature equivalent formulations which makes it possible to generalize different existing formulations. For this purpose, as an example, the power law formulation was used for the definition of the master time. The method introduced here also contributes a further framework for a unification of established time-temperature equivalent formulations, for example the time-temperature superposition principle and time-temperature parameter models. Results show, with additional normalization conditions, most of the developed time-temperature parameter models can be treated as special cases of the new formulation. In the aspect of the arrow of time, the new defined master time is a bended arrow of time, which can help to understand the corresponding physical meaning of the suggested method

Study On Coexistence Of Brittle And Ductile Fractures In Nano Reinforcement Composites Under Different Loading Conditions

Experimental study on high volume fraction of metallic matrix nano composites (MMNCs) was conducted, including uniaxial tension, uniaxial compression, and three-point bending. The example materials were two magnesium matrix composites reinforced with 10 and 15% vol. SiC particles (50 nm size). Brittle fracture mode was exhibited under uniaxial tension and three-point bending, while shear dominated ductile fracture mode (up to 12% fracture strain) was observed under uniaxial compression. The original Modified Mohr–Coulomb (MMC) fracture model (Bai and Wierzbicki in Int J Fract 161:1–20, 2010; in a mixed space of stress invariants and equivalent strain) was transferred into a stress based MMC (sMMC) model. This model was demonstrated to be capable of predicting the coexistence of brittle and ductile fracture modes under different loading conditions for MMNCs. A material post-failure softening model was postulated along the damage accumulation to capture the above two different failure modes. This model was implemented to the Abaqus/Explicit as a material subroutine. Numerical simulations using finite element method well duplicated the material strength, fracture initiation sites and crack propagation modes of the Mg/SiC nano composites with a good accuracy. The proposed model has a good potential to predict fracture for a wide range of material with strength asymmetry and coexistence of brittle and ductile fractures modes

A One-Dollar, Disposable, Paper-Based Microfluidic Chip for Real-Time Monitoring of Sweat Rate

Collecting sweat and monitoring its rate is important for determining body condition and further sweat analyses, as this provides vital information about physiologic status and fitness level and could become an alternative to invasive blood tests in the future. Presented here is a one-dollar, disposable, paper-based microfluidic chip for real-time monitoring of sweat rate. The chip, pasted on any part of the skin surface, consists of a skin adhesive layer, sweat-proof layer, sweat-sensing layer, and scale layer with a disk-shape from bottom to top. The sweat-sensing layer has an impressed wax micro-channel containing pre-added chromogenic agent to show displacement by sweat, and the sweat volume can be read directly by scale lines without any electronic elements. The diameter and thickness of the complete chip are 25 mm and 0.3 mm, respectively, permitting good flexibility and compactness with the skin surface. Tests of sweat flow rate monitoring on the left forearm, forehead, and nape of the neck of volunteers doing running exercise were conducted. Average sweat rate on left forearm (1156 g·m−2·h−1) was much lower than that on the forehead (1710 g·m−2·h−1) and greater than that on the nape of the neck (998 g·m−2·h−1), in good agreement with rates measured using existing common commercial sweat collectors. The chip, as a very low-cost and convenient wearable device, has wide application prospects in real-time monitoring of sweat loss by body builders, athletes, firefighters, etc., or for further sweat analyses