Fuel irradiated, porosity

Any particular fuel cycle might employ some, or all of these features, as needed. In addition, advanced characterization techniques will help to elucidate the relationship between fuel properties and fuel performance for advanced fuels. Examples of such innovative techniques include the measurement of thermal diffusivity, porosity, density, or the oxygen potential of irradiated fuel, use of advanced techniques for measuring the diffusion coefficient of fission gases (Hocking et al. 1998), and methods to accurately determine plutonium distribution in MOX fuel. 

The thermal conductivity of the fuel varies with temperature and is affected by manufacturing methods, the percentage of the porosity of the fuel, bumup, fission gas release, and deviation firom stoichiometry. As such, there are uncertainties in the reported thermal conductivities. For UO2, the uncertainty is about 10% for temperatures below 1727°C (2000 K), while the uncertainty increases up to 20% for temperatures between 1727°C (2000 K) and 2847°C (3120 K) (IAEA-TECDOC-1496, 2006). Fig. 18.2 shows UO2 thermal conductivity profiles as a function of fuel temperature for various percentages of theoretical fuel density, manufacturing, stoichiometry, and irradiation. Fig. 18.3 shows the impact of porosity and irradiation on thermal conductivity of UO2. Thermal conductivity is shown for unirradiated UO2 and irradiated UO2 with a neutron flux of 1.16 x 10 neutrons/cm at 527°C (800 K) before testing. In addition. Fig. 18.4 shows the uncertainty associated with the thermal conductivity of UO2 for various percentages of fuel porosity. In these figures, the TD of UO2 is considered to be 10,960 kg/m. ... 

---