Power plants, including nuclear power plants regularly employ tanks whose contents need to be kept isolated from atmospheric conditions. One way to satisfy these requirements is to provide a liner for the tank which completely fits the interior shape of the tank but floats on top of the tank contents when the tank contains fluid. As the volume in the tank changes, the liner or diaphragm accommodates the changes in volume by sliding along the tank walls. To allow free movement of the diaphragm, management of the gas volume above the fluid and behind the diaphragm is of prime importance. The work described in this paper elaborates on the conditions required to prevent the tank diaphragm from becoming damaged. To develop potential failure modes, the kinematics of the diaphragm and the interaction with the gas volume between the diaphragm and the tank fluid are considered in detail. The developed model is applied to the case of a condensate storage tank at Comanche Peak Nuclear Power Plant (CPNPP). Two physical scale models of the tank were constructed and tested to validate the model and allow the safe operation principles to be quantified for use in the operation of the condensate storage tank at CPNPP. The work allowed CPNPP to design appropriate periodic checks and maintenance activities to ensure the diaphragm will not be damaged due to tank volume changes while still ensuring the required water chemistry criteria for the tank contents can be met.
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