Uncertainty accommodating dependencies

The rate-determining step in this reaction sequence is reaction (reaction (2.85)) making ozone destruction linearly dependent on [XO]. The fraction of HOX that photolyses to give back OH depends critically on the accommodation coefficient of HOX on aerosols. Currently, there is a large uncertainty in this parameter. An important side effect of Cycle II is the potential for the reduction of the [H02]/[0H] ratio by consumption of HO2. The inorganic halogen chemistry described is summarised in Figure 24. 

VI.29. Any safety factors that might be applied to Eq. (VI.3), or to the parameters that make up Eq. (VI.3) and its elastic-plastic extensions, must account for uncertainties in the calculation or measurement of these parameters. These uncertainties might include those associated with the calculation of the state of stress in the package, the examination of the package for defects, and the measurement of material fracture toughness. Thus the overall safety factor required depends on whether the values used for the different input parameters are best estimate (mean) values or upper bounds for loading parameters and postulated defect sizes and lower bounds for fracture toughness. In particular, concern about uncertainty in NDE can be accommodated by appropriate conservatism in the selection of the reference flaw. 

The mass absorption coefficient does depend on the chemical composition. Example values (m / kg) for 60 keV y rays are polyethylene = 0.020, water = 0.021 and manganese = 0.105. If the solid phase is made up of only one compound, this effect can be accommodated during calibration. However if the transported material is a variable mixture of two or more components an uncertainty will be introduced into the measurement. 

Ross et al. (1988) have developed a correlation, shown as Eq. [18.39], for the calculation of the thermal conductivity of UN, in W/mK. In Eq. [18.39], T is the temperature in K. This correlation, which has an uncertainty within 10%, calculates the thermal conductivity of UN fuel with 100% of TD. In general, nuclear fuels are manufactured with porosity to accommodate for the gaseous fission products. Therefore, it is necessary to determine the thermal conductivity of a fuel based on its porosity. Kikuchi et al. (1972) have developed a correlation, shown as Eq. [18.40], which can be used to calculate the effective thermal conductivity of porous UN fuel as a function of percent porosity. InEq. [18.40], the coefficient is independent of temperature and has a value of 1.79 0.05 for porosities below 10%. Nevertheless, becomes temperature dependent when porosity increases beyond 12%. The value of varies from 1.38 0.12 at 300°C to 0.09 0.05 at 1300°C (Kikuchi et al., 1972). 

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