Devices to Mitigate Gas Entrainment in the Surge Tank of PFBR

Surge tank is one of the important components in the secondary circuit of a typical sodium cooled fast breeder reactor, provided to take care of pressure surges in case of a sodium water reaction in Steam Generators (SG). The blanket of argon cover gas at the top of the tank acts as a cushion for the surges. The argon gas above the free surface of sodium in the tank is a source of entrainment into the sodium which is undesirable from the consideration of effective heat transfer in Inter mediate Heat Exchanger (IHX) and SG cavitation in pumps and operational problems of continuous feed and bleed of cover gas, thus leading to unfavourable reactor operating conditions. To investigate the phenomenon of gas entrainment in surge tank, hydraulic experiments were conducted in water using 1/12 scaled model. The minimum height of liquid column in the tank when gas entrainment is completely avoided was established. Different methods to mitigate gas entrainment were tested in the model and a combination of porous plate and stiffener ring was found to be optimum in reducing the liquid column required to mitigate gas entrainment in surge tank.