[en] A major concern in the design of power reactors is that sufficient cooling capability be provided to keep fuel element clad temperatures below specified values, even for a postulated break in principal coolant loop components such as the main recirculation loop pipe. Therefore, it is necessary to be able to predict reactor system performance in such a loss-of-coolant accident (LOCA) and to evaluate accident preventing and/or mitigating steps in the design of he system. As a part of the continuing effort for improving and advancing safety technology, the C-E/EPRI Two-Phase Pump Performance Project is designed to provide basic data on the reactor coolant recirculation pump performance under two-phase flow LOCA conditions. Present pump analytical models generally in use for LOCA calculations employ homologous flow relationships to derive head and torque behavior in the two-phase flow regimes, and an empirical head degradation factor based on limited experimental information is generally used. This project is aimed at providing sufficient steady-state and transient two-phase empirical data to improve the presently used analytical modeling. Pump overspeed characteristics will also be examined