A Thermocouple Self-heating Test for Leak Detection in a High Level Liquid Waste (HLLW) Storage Tank

Abstract

Following the discovery of an internal leak in one of three ¼ inch diameter re-entrant thermowell tubes in an HLLW storage tank, a simple and non-invasive liquid detection method which consists of monitoring the temperature of the thermocouple inside the thermo-well before and after a brief period of thermocouple resistive heating, has been developed. The heat transfer rate, and consequently the temperature trend, is markedly different depending on whether or not liquid is present inside the thermo-well. Application of this method to determine the state of the remaining two thermo-wells of the storage tank has resulted in a significant reduction in uncertainty for controlling radiological risks and for developing and deploying investigation and remediation procedures. The method continues to be used regularly to monitor the state of one of the thermo-wells to ensure continuing safety for tank operations.