Analytical and Numerical Assessment of Thermally Induced Pressure Waves in the IFMIF-DONES Liquid-Lithium Target

The intended steady-state operation conditions of the International Fusion Materials Irradiation Facility-DEMO Oriented Neutron Source (IFMIF-DONES) target system are based on the D+ beam stationary running at full nominal power (5 MW). Nevertheless, critical situations can occur in the case of unavoidable sudden events like beam trips. The instantaneous variation in the heating power deposited in lithium when the beam is rapidly switched between ON-and OFF-states leads to thermal expansion, which is compensated by the compression of the target material, resulting in locally high pressures and a pressure wave propagating through the target toward the back wall. Besides the tensile stress of the back wall structure caused by shock pressure waves, undesirable cavitation may occur, when pressure waves are reflected leading to negative pressures. For this purpose, analytical and numerical thermohydraulic analyses of the effects generated in lithium during the beam-on/beam-off switches are performed. The pressure wave development inside the Li-target has been analyzed numerically with the computational fluid dynamics (CFD) code Star-CCM+. The simulation of the thermally induced pressure in the Li-target shows that for normal operation conditions, peak pressures of about 0, 3 MPa can be reached. In both 'beam-on' and 'beam-off' cases, a zone with a negative static pressure flow forms in the Li-target. The results obtained from the analytical and numerical analyses of the thermally induced pressure waves are discussed concerning potential cavitation and stability of the lithium free-surface flow. The simulation results served as input for the analysis of fatigue effects occurring in the target structure during sudden beam-on/beam-off events.