A nuclear reactor system comprising a nuclear reactor, a steam generator and a mist removal separator vane assembly installed in the steam generator, the demister separator vane assembly comprising: a vane bank having a plurality of vanes spaced in close proximity to one another, and a drain trough located below the vane bank, the vane bank and the drain trough extending substantially over a horizontal length of the demister separator vane assembly, wherein the plurality of vanes which extends downwardly toward the drain trough through a vertical length of the vane bank, characterized by an in-situ cleaning fixture for removing scale from the vane bank while the demister separator vane assembly is positioned within the steam generator, the in-situ cleaning fixture comprising: an injection chamber positioned above the vane bank so that the vane bank is positioned between the injection chamber and the drain through, the injection chamber having an inlet and a plate forming a bottom of the injection chamber and extending substantially over the horizontal length of the vane bank, the plate having a plurality of openings formed therein; and a means for connecting a cleaning fluid source to the inlet of the injection chamber, wherein the injection chamber is designed to receive cleaning fluid from the cleaning fluid source, to pass the cleaning fluid through the openings in the plate, downwardly along the plurality of vanes through the vertical length of the vane bank and into the drain trough. a vane bank having a plurality of vanes spaced in close proximity to one another, and a drain trough located below the vane bank, the vane bank and the drain trough extending substantially over a horizontal length of the demister separator vane assembly, wherein the plurality of vanes which extends downwardly toward the drain trough through a vertical length of the vane bank, characterized by an in-situ cleaning fixture for removing scale from the vane bank while the demister separator vane assembly is positioned within the steam generator, the in-situ cleaning fixture comprising: an injection chamber positioned above the vane bank so that the vane bank is positioned between the injection chamber and the drain through, the injection chamber having an inlet and a plate forming a bottom of the injection chamber and extending substantially over the horizontal length of the vane bank, the plate having a plurality of openings formed therein; and a means for connecting a cleaning fluid source to the inlet of the injection chamber, wherein the injection chamber is designed to receive cleaning fluid from the cleaning fluid source, to pass the cleaning fluid through the openings in the plate, downwardly along the plurality of vanes through the vertical length of the vane bank and into the drain trough. an injection chamber positioned above the vane bank so that the vane bank is positioned between the injection chamber and the drain through, the injection chamber having an inlet and a plate forming a bottom of the injection chamber and extending substantially over the horizontal length of the vane bank, the plate having a plurality of openings formed therein; and a means for connecting a cleaning fluid source to the inlet of the injection chamber, wherein the injection chamber is designed to receive cleaning fluid from the cleaning fluid source, to pass the cleaning fluid through the openings in the plate, downwardly along the plurality of vanes through the vertical length of the vane bank and into the drain trough.