Improved sodium pool temperature control in a sodium exposure test cell

In this paper we discuss a design change to the sodium exposure test cell (SETC) developed by JPL for evaluating alkali metal thermal to electric conversion (AMTEC) electrodes. This change, the addition of an antechamber to contain the sodium pool, was made to improve the control of the sodium pool temperature in the test, in order to improve the consistency and repeatibility of the electrode performance measurements. Experimental results and post test analysis showed that the change was very successful in controlling the location and temperature of the sodium pool. Using heater tape capable of higher temperature operation, we were able to duplicate electrochemical impedance spectroscopy results from earlier SETCs. These results indicate that when earlier SETC sodium pool temperatures were measured at 210-240°C, the effective sodium pool temperature was actually 385-400°C. The change in the overall length of the experimental apparatus also moved the specimens into a region in the oven with a flatter temperature profile, reducing the temperature gradient between the samples from 50-60°C to 10-20°C