The in-pile measurement of thermal conductivity of UO2 vibratory compact

This report describes the measurement of thermal conductivity of UO2 vibratory compact directly in-pile by aiming to measure at high temperature near to melting point of UO2 and also to measure for longer irradiation period. The instrumented capsule made use of a tantalum gas bulb thermometer and null-balance diaphragm type pressure transducer to monitor fuel center temperature. The fuel specimen was doubly contained in two concentric thin walled stainless steel shells. The annulus between these two containers was filled with stacked niobium sleeves, in which three pairs of stainless steel sheathed, Al2O3 insulated chromel-alumel thermocouples were positioned 120 degrees apart for the purpose of measuring heat generated in fuel. A secondary gas was introduced into the transducer on the upper side of the diaphragm from an out of pile control system. When the secondary gas pressure exceeded the primary gas pressure, an electrical contact was broken and the pressure was recorded. The center temperature was measured as a function of gas pressure in the primary system. The measurement of thermal conductivity was made up to 24000C. In addition, the measurement was made, although at lower temperature such as below 8000C, continuously for fifteen days. (Auth.)