Thermal fissions, percentages

The last cause of neutron loss is the absorption of the thermal neutrons by the rather than the. Only the latter absorption leads to fission and the creation of daughter neutrons. The relative amount of absorption by the cannot be diminished except by increasing the percentage of in the U or by adding 49, i.e., by enriching the U. 

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. ... 

Even though the above equations capture the variation in thermal conductivity of Th02 as a function of temperature, the thermal conductivity of Th02 also changes due to manufacturing methods, the percentage of the porosity of the fuel, bumup, fission gas release, and deviation from stoichiometry. Rg. 18.5 shows the variation in thermal conductivity of Th02 for various porosities and densities as a function of temperature. 

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