NATURAL CIRCULATION Fluid FlowBoth of these actions will help ensure steam/vapor pockets are not formed in the RCS where theywould restrict RCS flow. Thirdly, maintain steam generator water level normal range. Thisprovides an adequate heat sink to ensure heat removal is sufficient to prevent boiling of the RCS.SummaryThe main points of this chapter are listed below.Natural Circulation Flow SummaryNatural circulation flow is circulation of a fluid without the use ofmechanical devices.Forced circulation flow is circulation of a fluid through a system by pumps.Thermal driving head is the driving force for natural circulation causedby the difference in density between two areas of fluid.Three items are necessary to support natural circulation:There must be a heat sink and a heat source.The heat source must be located below the heat sink.Flowpaths must exist between the warm fluid and the cold fluid.Generally, the greater the temperature difference, the higher the naturalcirculation flow rate.Natural circulation in a PWR can be verified by monitoring:RCS DT - 25%-80% full power valueTHot / TCold- steady or slowly decreasingS/G steam pressure - tracking RCS temperatureNatural circulation in a PWR can be enhanced by:maintain pressurizer level >50%maintain RCS 15oF subcoolingmaintain adequate heat sink, S/G level normal rangeHT-03 Page 40 Rev. 0
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business