Strömungsmechanische Simulation und experimentelle Validierung des kryogenen Wasserstoff-Moderators für die Europäische Spallationsneutronenquelle ESS

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

Cryogenic hydrogen cooling of heated moderator vessel

In ESS, a pulsed proton beam of 5 MW mean power will hit a tungsten target to generate neutrons by spallation. The pulses are 2.86 ms long and occur with 14 Hz; the power within a pulse is 125 MW. Only centimeters from the target, the neutrons are moderated by liquid hydrogen in aluminium vessels. The deposited power heats the surrounding structures and fluids which are circulated and cooled. The hydrogen is operating at 15 bar and average temperature between 17 and 21 K, i.e. above the critical pressure 12.8 bar, but below the critical temperature 32.9 K. During the pulses, the peak heat deposition in the aluminium is 15 W/cm3 and in the hydrogen 4 W/cm3. If the cooling of the aluminium is neglected during one pulse, the temperature increases to 34 K. That is above the critical temperature, where physical properties change strongly with temperature. Therefore the conjugate heat transfer has to be investigated in detail. This work includes 1D principal transient calculations of a general configuration as well as CFD simulations of the heating and cooling of a specific design. The 1D calculations are performed using GNU/Octave and the CFD using ANSYS/CFX. It is concluded that with an inlet temperature of 17 K, the wall temperature can be kept below the critical temperature in the general configuration and sufficient cooling can be ensured in the investigated specific design

Thermal Hydraulic and Thermo-Mechanical Design of the Proton Beam Window for ESS

The proton beam window for the European Spallation Source ESS will separate the 1 bar monolith helium atmosphere and the accelerator vacuum. In medium power spallation sources like ISIS, SINQ or the SNS source in Oak Ridge, cylindrical or spherical double walled water cooled windows are used, but during the design of the beam window for the spallation source SNS it became obvious, that this concept is already pushed to its limits at a beam power of 1.4 MW. A novel design concept called pan-pipe design was proposed for the ESS-PBW, which is optimized for high coolant pressures – as helium is the designated coolant for the PBW at ESS - and the typical pressure difference of 1 bar over the window. In the present study the detailed thermo-mechanical design of the PBW made of aluminium is shown. The main focus of the investigations was set on fatigue loading due to mechanical and cyclic thermal loads and on an optimized flexible interface between the PBW and its massive frame