Nominal Conditions and Uncertainties

The MCSTs are evaluated for three bumup states, BOEC, MOEC (middle of equilibrium cycle) and EOEC. The nominal conditions at these bumup states are shown in Table 7.20 [1]. The nominal MCST over the cycle appears at EOEC and is 645.3°C. 

The system parameter uncertainties taken into account here are listed in Table 7.21 [1]. Calibration errors associated with measurement of the feedwater temperature are typically in the range of 2.22°C. The standard deviation for this calibratimi error is 1.27°C in a uniform distribution. The t3q ical measurement error of the feedwater flow rate is 2% of the nominal value. The standard deviatirMi of 2% error is 1.15%, of the nominal value for the uniform distributiOTi. The uncertainty of the core power level is caused by the calibration error of core total power measurement and cmitrol system dead band. A typical error (2% of the nominal value) is considered. Then, the standard deviation of the total power level is 1.15% considering the uniform distribution. The system pressure uncertainty of 200 kPa is considered. The standard deviation of the system pressure is 115 kPa, considering the uniform distribution. 

The nuclear hot factors are used to consider the power distribution in the core. It consists of three hot factors, radial, local, and axial nuclear. The radial nuclear enthalpy rise hot factor is defined as the ratio of the hot assembly power to the average assembly power. The local nuclear enthalpy rise hot factor is defined as the ratio of the hot fuel rod power to the hot assembly average power. Finally, the axial nuclear enthalpy rise hot factor is defined as the ratio of the maximum axial plane power to the average plane power. In the full statistical treatment, the nuclear enthalpy rise hot factor is not an absolute value. It also varies around the nominal value with given tolerance. The uncertainty of the nuclear enthalpy rise hot factor is mainly induced by neutronic calculatirai errors. A typical error of 2% for each component of the hot factors is considered. If the normal distribution is assumed, the standard deviation of each hot factor is 1% of the nominal value. Table 7.22 [1] shows the uncertainties of the nuclear enthalpy rise hot factors considered here. 

The engineering temperature rise hot channel factors account for flow conditions and tolerances of the hot coolant channel. They arise from the tolerances of dimensions, fissile contents, data processing, and so on. The engineering factors consist of two parts. One is the coolant temperature rise hot channel factor. The other is the film temperamre rise hot channel factor. The engineering temperature 

System parameter Nuclear enthalpy rise Engineering temperature rise Peak cladding surface temperature 

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