Search

A new shutdown system that does not rely on absorber rods, is being developed at SCK.CEN and UCL for application in Liquid Metal Reactors (LMR). The system consists of tubes filled with absorber particles. During normal operation, these particles are kept above the active core by means of a metallic melt seal. In case of an accident, the system is activated by the temperature increase in the coolant. This leads to melting of the metal seal, releasing the absorber particles into the core. The resulting flow of the particles has been studied both experimentally, and with Discrete Element Method (DEM) simulations. This paper focuses on the second important aspect of the safety system, being the melting and flowing of the metallic seal in interaction with the solid absorber particles moving through the molten seal. [ABSTRACT FROM AUTHOR]

This paper describes a sensitivity study of the flow of granular fertiliser particles on a spinning disc using a discrete element model. The aim was to get a qualitative insight in the influences of individual physical properties of the particles (such as friction coefficient, restitution, and shape) as well as their bulk behaviour on the resulting spread pattern. The results show that certain particle properties, particularly friction coefficients, have a large influence on the spread pattern, and hence should examined carefully in the process of producing granular fertilisers, perhaps by particle coating, or taken into account when applying the fertiliser in the field. Other properties, such as particle stiffness hardly affect the results. Furthermore, it was shown that the friction coefficient and shape of a particle strongly interfere in their particular influence on the spread pattern. Overall, the discrete element model could provide a powerful instrument for the manufacturers in the development of new kinds of spreaders and fertilisers. [Copyright &y& Elsevier]

Abstract: Modeling approaches for centrifugal fertilizer spreaders have so far been based on analytical expressions for single particle trajectories derived in the early 60''s. However elegant this approach was, it suffers from several disadvantages, the most important of which is failing to incorporate the interaction between the particles in the flow. This paper is the first in a series aiming at simulating the complete spreading process based on the laws of physics and a physically meaningful model for the interactions between the particles, c.q. the contact forces. The result is a model that allows the development of a deeper understanding of the physics underlying the spreading process and provides better predictions. In this paper the model is presented in detail and a series of simple computer experiments are analysed and compared to theoretical predictions. Also, single particle trajectories from DEM simulations are compared to experimental results. Further, some effects of the model parameters are analysed. This paper demonstrates that the model is not only capable of producing realistic simulations, but also provides detailed insight in the physics of the spreading process. [Copyright &y& Elsevier]

The performance of centrifugal spreaders can be evaluated by measuring their fertiliser distribution patterns in spreading halls. Compact experimental equipment was used to measure the tangential and the cylindrical distribution of the particle flow close to the edge of the disc. Additional information on the positions and velocity vectors of the particles when leaving the disc was obtained by photogrammetry. From these data, standard distribution patterns have been computed by means of a computer program simulating the ballistic flight of the particles.Experiments were conducted with a single commercial centrifugal spreader with conical discs, which can be supplied with short or long vanes. Both vane types are combined with two different types of fertilisers. There is a good qualitative agreement between the measured and simulated distributions. Quantitatively, the difference between experimental and simulated distributions amounts to a shift and an expansion in the angular direction and a contraction in the radial direction. Conclusive evidence is reported that the predicted patterns respect trends that can also be observed in experimental patterns due to variations in fertiliser properties or spreader settings. Consequently, the predicted patterns can be used to investigate such trends. Further improvements of the simulation model and/or the implementation of the experimental facility are needed before the proposed evaluation method can completely replace spreading hall measurements. [Copyright &y& Elsevier]

Abstract: Generation IV (GEN IV) reactors promise higher safety levels compared to current generation II or III reactors, one of the most important safety aspects of any reactor is the ability to shutdown the reactor in any condition. The shutdown mechanism in current designs of liquid metal cooled Gen IV reactors is based on absorber rods. Although these rod based systems are duplicated to provide redundancy, they all have a common mode of failure as a consequence of their identical operating mechanism; possible causes being a largely deformed core or blockage of the rod guidance channel. To achieve the goal of higher safety, a complementary scram system is desirable. In this paper an overview of existing solutions of such a complementary system is given and a new concept based on absorber particles and the existing solutions is proposed. This original system, which is not rod based, is under investigation and its feasibility is verified both by experiments and simulations. [Copyright &y& Elsevier]