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Air flow in CNGS tunnel structures at CERN: a study for ensured operational safety
2002 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

CERN, the European Laboratory for Particle Physics, is an international collaboration formed by 20 member-states in Europe to provide hi-tech research facilities for physics. CERN offers state of the art particle accelerators, detectors and research areas for probing into the mysteries of our smallest constituents. The second largest experiment presently being prepared at CERN is the CERN Neutrinos to Gran Sasso (CNGS) project. By allowing neutrinos to travel a far distance, scientists hope to be able to prove that neutrinos have a mass by showing the existence of neutrino oscillation. One of the most crucial parts of the project is the decay of unstable particles into neutrinos. This takes place in a one kilometre long evacuated tunnel. This tunnel is connected to a control room and the rest of the underground accelerators at CERN. Having such a large evacuated volume connected with areas where people will be situated imposes great security risks that have to be evaluated. The final aim of the study is to determine parameters describing the flow, such as pressure and temperature variations as well as velocities, arising in the case of a rupture of the structure separating the low- and high-pressure areas. These parameters are to be used to determine whether the risk of any danger to the personnel or structures can be ruled out or whether a full study, with more exact geometry and complex flow conditions, is needed to ensure the operational safety. From the model implemented, it is possible to obtain reliable results for the flow connected with the rarefaction wave progressing in the tunnels. This gives rise to a pressure drop of 24kPa over slightly less than one second, and a velocity increase of the air from zero to 67 m/s in the area of the control room. The velocity increase corresponds to an acceleration of 6.2 g. The change in temperature is more moderate, with a drop of 21 Kelvin. Due to numerical instabilities imposed by the positioning of a pressure boundary in the model, no reliable results are obtained for the progression of the expected shock wave in the area of the control room. This is not dependant on complications arising from the shock, but on the errors transferred from the pressure boundary to the area of the control room. The flow generated by the shock itself is well captured in the code. On basis of the values for the pressure gradient and the acceleration of the air in the area of the control room, the evolved flow is judged to be severely dangerous to any personnel in the area. However, these predictions are based on a simplified simulation model, which gives over estimations of the flow effects. This lead to the conclusion that the simulations need to be developed further to be able to determine whether it is safe to implement the project with the present design, or whether safety measures need to be taken.

Place, publisher, year, edition, pages
Keyword [en]
Technology, air flows CNGS CERN safety shocks rarefactions fluids gas, dynamics
Keyword [sv]
URN: urn:nbn:se:ltu:diva-50830ISRN: LTU-EX--02/024--SELocal ID: 80ce66e0-aed3-45bf-a8cf-37100ee1e143OAI: diva2:1024193
Subject / course
Student thesis, at least 30 credits
Educational program
Mechanical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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