[en] The major initial objective of the in-core molten fuel pool program at Sandia has been to develop a versatile experiment in which relative heat fluxes and structural ablation could be studied using real materials under typical temperature and heating conditions. The initial experiment series is designed to prove containment design, test ultrasonic thermometers, and provide material interaction data. The first two molten fuel pool experiments, MP-1 and MP-2, were successfully conducted in the Annular Core Pulse Reactor (ACPR) on June 24 and July 29, 1977. These first two experiments demonstrated the adequacy of the experiment package for heating and containment of UO₂ to melt. They have shown the usefulness of ultrasonic thermometry for making multiple temperature measurements to the melting point of UO₂, but also indicated that some problems remain to be solved in this application of the technique