Thursday, 28 April 2016

The first step is accomplished!

Hello readers,

Today, I would like to talk about the first part of my research project. Every good researcher, and here I include my TRUSS colleagues, consecrate time to refresh technical concepts and perform a literature review. Fortunately, nowadays we have internet and thousands of articles are accessible online. It makes the search for technical information much easier but, on the other hand, reading and filtering that information still takes a lot of time. You can imagine how tedious can this work be, but it is critical to get into the state of the art, become aware of your level of knowledge, discover interesting approaches and set your own path.

In my case, this stage lasted for about 6 straight months due to the complexity of the topic. However, it doesn’t bother me since I truly believe that successful results only come from the right initial conditions. Just like in structural transient analysis! Even if my research topic is a very specific problem in a special domain, I have been able to find out interesting information about the different complex problems that affect the racks seismic behavior. Actually, one could spend his entire life reading about structural dynamics, fluid-structure coupling, computation algorithms, uncertainty analysis, etc. However, besides that general bibliography, there also exist some works particularly focused on the seismic behavior of racks. Since the free-standing concept has been developed quite recently, most of these articles have been written during the last 25 years. It is not surprising that this kind of research was carried out in countries where the nuclear industry is well established as USA, France and Japan. The ground-breaking authors where constrained by the computing capacity of their time, so they used rudimentary numerical 1-rack numerical models occasionally supported by real scale physical models. As a consequence, very few studies take into consideration the interaction effects between the different racks nestled in the depths of the spent fuel pool. Nevertheless, this a priori hidden interaction caused by the inertial coupling of the water volume has proved to be decisive when clearance between units is small. In other words, there is still much work to do!

Installation of a rack unit as a part of a rack system

In the same time, I have approached the ENSA’s analysis methodology currently applied in the dynamic analysis of the nonlinear response of HDSFS racks. This cost-effective methodology considers the Fluid-Structure Interaction (FSI) through the hydrodynamic mass concept and takes advantage of the thermal analogy to perform the ensemble of calculations in unique software. It is in agreement of the international guidelines, validated by the nuclear authorities and implemented in ANSYS Mechanical thanks to the expertise of my supervisor Mr. Costas.

In order to summarize all of this work, I have written two technical papers highlighting my personal conclusions. The first describes 6 sources of uncertainty in design identified to date, and the second details the current analysis methodology and provides some numerical results. They are already submitted for approval to a couple of international congress planned for this summer. I promise to keep you posted on the progress.

See you down here soon!

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