Response of Liquid Lithium Layers to Neutron and X-Ray Pulses

Abstract

Many inertial confinement fusion reactors will employ liquid lithium to breed tritium, to remove heat from reactor vessels, and to protect the interior walls of the vessel. Heat loads on the liquid lithium will consist of intense pulses that are short in comparison to hydrodynamic and thermal relaxation times and therefore will generate pressure pulses and/or pressure waves. The generation process is investigated analytically and numerically. Analytic solutions are derived for liquid blankets with thicknesses comparable to the neutron energy deposition depth contained between two structural shells and for free surface layers with thicknesses much smaller than the depth of neutron energy deposition. Results indicate that the amplitudes of the neutron-generated pressure waves are comparable to the mean pressure rise that would be obtained if the energy were deposited so slowly and uniformly that the waves did not develop. Numerically investigated are pressure pulses in lithium layers, which are initially at the vapor pressure. Results indicate that rapid heating occurs at constant specific volume (isochorically) and therefore results in a sharp and intense pressure rise. However, the resulting pressure wave dissipates after propagating only a few millimetres through the layer if the lithium contains any fraction of the vapor phase.