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Eingeladener Vortrag
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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.
Many substances react with water in such a way that flammable gases are formed. For transport issues this reaction may possess a considerable hazard especially if the cargo is wetted by rain or by water from other sources. In the UN Recommendations on the Transport of Dangerous Goods these kinds of problems are addressed. The UN test N.5 'Test method for substances which in contact with water emit flammable gases' corresponds to this hazard. Classification according to the test method is done by measurement of the gas evolution rate of the flammable gas by any suitable procedure. At BAM a gravimetric approach is used to measure the gas evolution rate. In this paper we present the evaluation of the apparatus by means of an absolute calibration routine utilizing a reaction where a known amount of gas is produced as well as the evaluation of important parameters influencing the gas evolution rate using different substances. It can be shown that the apparatus is capable of measuring absolute gas volumes as low as 6 mL with an acceptable error of about 17% as determined from the reaction of Mg with demineralized water.
Amuay refinery disaster (2012) is another recent example of Vapor Cloud Explosion (VCE) and fire accidents preceded by Buncefield (2005), Puerto-Rico (2009) and Jaipur (2009), respectively [9]. The incident has left many safety issues behind which must be repeatedly addressed. Unfortunately, the lessons taught by previous similar events are just not understood carefully. It reveals that the proper safety measures for such facilities were either underestimated or were not accounted seriously. Consequently, the resulting overpressures from explosion and the subsequent thermal radiation from tank fires have once again proved to be disastrous to both mankind and infrastructure. This article highlights the aftermaths of Amuay incident and addresses the challenges put forward by it. Furthermore, a comparative study is performed between such incidents to analyze the similarities and how they could have been avoided.
Two-phase CFD (Computational Fluid Dynamics) model for characterising the spill-over/dispersion of peroxy-fuels is presented. The model is independent of type and burning rate of the spilled/dispersed fuel and considers only overflow Reynolds number (Re) to characterise the spill/dispersion behaviour. Additional simulations are performed for LNG (Liquified Natural Gas) dispersion and it is found that the model can be used for different fuels within a defined range of Re. Different scenarios with Re = 100 to 3 × 105 are investigated covering a wide range of mass flow rates, opening sizes and viscosities. Depending on Lower Flammability Limits (LFL) of the fuels spill/dispersion (vapour cloud) diameters (DCFD) and heights (hCFD) are predicted. A generalised correlation between DCFD and Re is established to predict the dispersion occurring at varying scales. The model is validated by: (1) conducting an extensive grid independent study; (2) comparing the results with the existing analytical methods and (3) comparing against the standard field test data on LNG dispersions.
Industrial fire and explosion hazards are most often also associated with the dispersion of toxic substances.
These substances can be gases, liquids, solids or in form of aerosols. The critical toxic exposure limits to People and enviroment from such substances are regulated by the concerned authorities of the countries. In order to comply with the defined regulation estimation of such critical limits must be carried out by different semi-empirical and phenomenological models/methods for risk assessment.
Many of such methods provide a qualitative estimation of time and space dependent extrimities of toxicity. The overwhelm development of computational capacity has made it possible to perform Computational Fluid Dynamics (CFD) simulation by solving the three-dimensional transport equations for mass momentum and species in lower and upper atmosphere, respectively. CFD simulation not only provides a detailed 3D distribution of toxic particulates/gases in the neighbourhood of the plant but also helps to study the worst-case sceanrios. In the past several small- and large-scale accidents occured in oil and gas plants in different parts of the world including the recent one in Rheinland refinery near Cologne in Germany. This work deals with this accident and provides a methodology to predict the critical exposure limits of smoke emitted by a toluene tank fire by means of CFD simulation.
We read the paper by Guo et al. [1] with interest. The authors have investigated the thermal decomposition kinetics and thermal hazards of 2,2′-azobis(isobutyronitrile), AIBN, by differential scanning calorimetry (DSC) and used the Advanced Kinetics and Technology Solutions (AKTS) software to predict the thermal stability of AIBN in ton and kg scale. The main conclusion of interest is that the self-accelerating decomposition temperature (SADT) of a 50-kg standard package is 63 °C.
Experiments according to a test specified in the UN Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, and numerical simulations by means of a finite element method are employed to determine the self-accelerating decomposition temperature of acrylic acid in a railroad tank car. The results demonstrate that the transport of acrylic acid in big tank cars is safe as long as some basic conditions are taken into account.