The energy exchanger, or pressure exchanger, is a rotating, axial flow machine which utilizes unsteady gasdynamic processes to directly transfer work between two gas streams. This report describes a program which has provided technology required for the development of efficient energy exchangers for power operation applications. The program contained three major elements: testing of a laboratory scale device, development of an energy exchanger flow model, and analysis of potential applications in advanced power generation cycles. The test energy exchanger was developed and tested over a range of operating conditions. This device transferred approximately 100 kW of mechanical power between two gas streams by simultaneously expanding one stream and compressing the other through pressure ratios of approximately 2.5. The efficiency of this transfer process was as high as 74%. Measurements were made of overall mass and enthalpy flows through the energy exchanger and of time-dependent anthered from site visits, thmined by 28-day MCC-1 tests (90/sup 0/C) for Cs, Sr, U and Nd are 0.8, 0.4, 1 x ld as shock-like intensity and direction variations as well as in spectral modifications of high-energy electron and proton fluxes.