Videometric void measurement in counter-current and stratified tow-phase flows

Due to a small leak (SBLOCA) in the cold leg of a PWR reactor with long failure of all coolant injection systems the reflux condenser mode can be important. This can occur if due to the loss of coolant only steam from the upper plenum flows into the hot leg into the steam generator. The steam condensate and flows at least partially back through the hot leg into the reactor pressure vessel (RPV). This counter-current two-phase flow in the hot leg can induce flow instabilities that impede the backflow of the water into the RPV. This counter-current flow limitation (CCFL) phenomenon is studied by a new videometric method. The determination of the local gas volume fraction was compared with electrical contact probe measurements.