Feasibility of Partial ZrO[subscript 2] Coatings on Outer Surface of Annular UO[subscript 2] Pellets to Control Gap Conductance

Abstract

The viability of depositing a thin porous coating of zirconia on the outer surface of an annular UO[subscript 2] pellet is investigated experimentally. Such a layer has been proposed to buffer the contact between the fuel and cladding, thus maintaining an appropriate balance of heat transfer from the pellet to the outer and inner cladding. MIT and Gamma Engineering commissioned laboratory studies of the feasibility of depositing a controlled thickness of porous zirconia on an oxide surface. Experiments were conducted at the Thermal Spray Laboratory at SUNY-Stonybrook to produce a thin layer of Yttria Stablized Zirconia (YSZ) on alumina wafers. The experiments concluded that it is possible to use plasma spray guns to produce 50% porous layers of 15–30 micrometer thickness. Measurements were conducted at the Vitreous State Laboratory of the Catholic University of America to determine the thermal conductance of aluminazircaloy and alumina-zircaloy-YSZ sandwiches as a function of applied pressure. A relation is developed to predict the conductance at such surfaces.