Strömungsmechanische Simulation und experimentelle Validierung des kryogenen Wasserstoff-Moderators für die Europäische Spallationsneutronenquelle ESS
Beßler, Yannick; Natour, Ghaleb (Thesis advisor); Singheiser, Lorenz (Thesis advisor)
Aachen (2020) [Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (XXIV, 154, xxxiii Seiten) : Illustrationen, Diagramme
The European spallation neutron source ESS is currently under construction and should start part-load operation in 2023. With an average proton beam power of 5 MW, it will become the most powerful spallation neutron source worldwide. A key component of a spallation neutron source is the cold moderator. At the ESS, the cold moderator will be operated with liquid parahydrogen at a temperature and pressure around 20 K and 10 bar respectively and is intended to slow down (moderate) the fast neutrons, released by the spallation process, to the required low velocity level. Latest particle-transport-simulations show that the neutron yield can be increased by up to 30 % by optimizing the existing cold moderator. The present dissertation therefore examines the technical feasibility of this new moderator for full-load operation of the European spallation neutron source ESS. The primary goal is to verify whether the cold moderator can be operated at full proton beam power or up to which beam power a safe operation is possible. In addition, the feasibility from the structural mechanical and manufacturing point of view will be assessed. In order to investigate the flow behavior in the cold moderator, a numerical flow simulation was first carried out. The flow guiding has been optimized for the best possible heat transfer because the pulsed proton beam causes an enormous fluctuation in thermal load. Furthermore, sources of errors of the simulation were identified and minimized. For this purpose, the model error of the flow simulation was determined by particle image velocimetry (PIV) comparison measurements. As part of the parameter studies, it turned out that the cold moderator can only be safely operated up to a proton beam power of approx. 3.4 MW under the given requirements and with a conservative consideration of all errors. Therefore, a several additional options were shown, by which the proton beam power might be significantly increased, and the goal of 5 MW would still be possible. The structural mechanical part of this work, in which the cold moderator was designed according to the nuclear code RCC-MRx, showed that the pressure vessel withstands all static and dynamic loads. Thereby the radiation as well as all loads in normal and abnormal operation were considered. Finally, an initial prototype of the optimized cold moderator has been manufactured and tested. The joining technology for the selected aluminum alloy AW 6061-T6 was of special importance, since this alloy is generally difficult to weld. Electron beam welding was used because it leads to lowest possible distortions and minimized local heat input. Finally, non-destructive tests were carried out to confirm the high quality of the manufacturing, and thus the suitability of the cold moderator for a safe operation under the extreme operating conditions.