Reverse flow in a pressure suppression system due to condensation instabilities

Abstract

The Vacuum Vessel Pressure Suppression System (VVPSS) is designed to protect the ITER reactor (Vacuum Vessel, VV) from an overpressurization accident. The VVPSS is mainly composed of four Vapour Suppression Tanks (VSTs) partially filled with water inside which venting pipes (spargers) are immersed to direct the steam in the subcooled pool to condense it. Since the maximum pressure allowed inside the VV is only 0.15 MPa, a sub-atmospheric pressure must be maintained inside the VSTs. During a series of experimental campaigns funded by ITER Organization to study and validate the correct operability of the VVPSS and conducted in a large-scale plant built at the B. Guerrini laboratory of the University of Pisa, pressure instability and reverse flow through the sparger holes have been observed. The analysis of acceleration signals recorded during this pressure inversion, showed large amplitude oscillations at low frequency due to the Condensation Induced Water Hammer (CIWH).