Thermodynamics and transport processes in reactor fuel

Abstract: Chemical thermodynamics and transport processes are inextricably linked in light-water reactor fuel rods. Two regimes can be identified, separated by their temperatures. During normal operation, the temperature at the center of the U02 pellet usually does not exceed lOOOOC, and most of the important chemistry takes place at the periphery, which is separated from the Zircaloy cladding by a thin(tens of microns) gas-filled gap. The temperatures here are typically 350-6OOOC. In a serious accident resulting in loss of cooling water circulating in the reactor's primary circuit, Severe fuel damage may occur. Conditions in this regime encompass temperatures from-1000 to 3000OC, the state of water is steam rather than liquid, and the system total pressure may be as low as 1 atm. This paper reviews the important chemistry-transport phenomena that occur in the normal-operation and severe-fuel-damage regimes. I Normal Operation Normal operation includes two sub regimes: operation with intact fuel rods and operation with defective rods. Intact Fuel Rod