Liquid metals, in our case sodium, may be used for heat storage in a tank on a commercial scale. One of the possibilities is to store the hot and the cold sodium in the same tank and to separate them by a movable plate. The axial position of the plate varies with the varying amount of hot and cold sodium. The axial position of the plate varies with the varying amount of hot and cold sodium. The plate should have a low thermal conductivity to reduce conduction between the upper and the lower part and hence to increase the efficiency of the device.
With such a construction, only one tank is necessary for the whole sodium inventory instead of two for hot and the cold one separately. It can be filled completely, because the external expansion tank that is necessary in any case in the related circuit is used to account for thermal expansion. As benefits for such a design, the walls keep wetted all the time during operation, and a permanent inert atmosphere in the storage tank can be avoided.
Due to the compact construction, this layout limits the sodium inventory and reduces the risk of leakages. Since the plate moves slowly, when the design is appropriate, thermal loads on the tank are limited. As the plate moves with the flat surface of the cold sodium, it should be impossible to be tilted.