Supercritical water flow-through test facility (SCW-TF) for the study of hydrothermal fluids is described. The hydrodynamic behavior of the flow-through reactor is examined from ambient to supercritical water conditions by performing residence time distribution measurements. The results indicate that at 25 MPa, the employed reactor configuration exhibits plug flow behavior with a small extent of dispersion over the temperature range from 298 to 773 K. The experimentally determined effective volume of the reactor was used for the calculation of mean residence times of the fluid in the "hot zone" of the flow-through system. The thermal stability of hydrazine in aqueous solution was examined along the 25 MPa isobar from 473 to 725K. The obtained first-order rate constant for the thermal decomposition of hydrazine increases from 3.73 x 10(-4) s(-1) at 473 K to about 0.31 s(-1) at 725 K. (C) 2010 Elsevier B.V. All rights reserved.