UO 2 properties affecting performance

Abstract

UO 2 has become the basic reference fuel material for the power reactor industry. The most widely used form is cylindrical, sintered pellets with finished densities in the range 92 to 97% of theoretical. This selection of UO 2 over other potential fuel materials is based on its excellent combination of chemical stability, especially to water reactor coolants; compatibility with potential cladding materials such as stainless steel and zircaloy; dimensional stability under irradiation; very high melting point; and straightforward, economical production from diffusion plant enriched, uranium hexafluoride. These desirable characteristics were recognized at a very early stage in the development of power reactors, and, as a result, the properties of UO 2 have been under intensive study for about 20 years. There has probably been more development work on UO 2 than all other fuel materials combined. The data cited are those most familiar to the authors that are believed to fairly represent a property or illustrate the relationship under consideration. In the first part of this report the basic UO 2 property data are presented and the effect of important variables such as density, temperature, stoichiometry, etc., are discussed. In the second part the property data are discussed in the context of their role in various fuel life-limiting mechanisms that have been shown to be of practical significance for UO 2-containing fuel rods.