A Sensor for Oxygen in a Potassium-Sodium Alloy

This project supports a research project to determine the configuration for heat exchanger welds in a space reactor. The reactor is a sodium-potassium (NaK) cooled reactor for use on future missions on the lunar surface or on Mars. Various types of welds in Type 316L stainless steel have been positioned in a furnace which is part of a NaK test loop. The specimens are bathed in circulating NaK at 600 degrees centigrade.

Since the oxygen concentration in the NaK is a major factor in corrosion of the weld specimens, it must be carefully monitored and controlled. However, few techniques are available for analysis of oxygen in alkali metals, and perhaps only one is reasonably available for continuous monitoring of oxygen. Electrochemical potential is the method selected to monitor oxygen concentration in the NaK loop, and this research project is to design and fabricate an electrochemical sensor to determine the oxygen concentration in NaK.

An existing automotive oxygen sensor was extensively modified for use in the NaK system. It incorporates a reference cell consisting of Bismuth/Bismuth Oxide and molybdenum electrodes. A system for calibration of the sensor at elevated temperatures was developed, and a calibration curve generated for use in the NaK test loop.