ON MICROWAVE EXPERIMENTS IN DIELECTRIC MEDIA TO SIMULATE NUCLEAR VOLUMETRIC HEATING

The use of microwave experiments in normal fluids is proposed for the approximation of the volumetric heating distribution in cryogenic flow of radiation heated deuterium in the advanced neutron source (ANS) co ld neutron source (CNS) planned for construction at Oak Ridge National Laboratory. The potential of such experiments is investigated by solv ing Maxwell's equations for microwave propagation and absorption in se veral noncryogenic model fluids. Included are an analytical Mie series solution for an idealized ANS CNS geometry and a solution in a more c omplex and realistic geometry by the computational finite difference t ime domain (FDTD) technique. Though data and anecdotal evidence sugges t difficulty with specifying a given volumetric heating distribution i n a boiling liquid in a microwave cavity, the computational results su ggest that CNS-like heating distributions can be obtained by using mic rowave irradiation. Two aspects of microwave heating are examined. The first is scale dependence of heating across various fluid particle si zes in a potentially complex multiphase flow, and the second is detail ed heating distribution across a realistic three-dimensional ANS CNS g eometry. By using a Mie series solution in spherical geometries to ind icate dependence of microwave heating on fluid particle size for flow scales relevant to ANS CNS flows, several fluids, including n-propanol and n-butanol, are found to show <20% variation in heating on scales from 0.01 down to 10(-7) m. By using FDTD computations, the expected A NS heating distribution in liquid deuterium is compared with heating d istribution under microwave irradiation for several different model fl uids. Good qualitative agreement is found between expected ANS heating distribution and microwave heating in the n-propanol and n-butanol fl uids including the heating asymmetry expected in ANS CNS flows. By usi ng this simulated heating distribution, volume-heated flow can be inve stigated. Expected results from such an investigation include flow reg ime determination, effects of nucleation phenomena, and other physical characteristics such as heating distribution, container shape, and fl uid properties.