Geometric Uncertainty Analysis of Fuel Assembly Based on Sub-Channel Model

Abstract There are inevitably geometric uncertainties during the machining and installation of fuel rods, such as the pitch and diameter of each fuel rod, which can lead to changes in the thermal and hydraulic characteristics of the reactor. In this study, a method is proposed to simulate geometric uncertainties as realistically as possible for subchannel models. In this method, each rod is disturbed individually, including the diameter of the fuel rod, the offset distance and the offset Angle. At the same time, a 3 × 3 rod bundle channel model of pressurized water reactor (PWR) is established based on the subchannel model, which contains 8 fuel rods and 1 guide tube. Latin hypercube sampling (LHS) method was used to extract samples, and different perturbations were made to 9 rods at the same time, and then the influence of geometric uncertainty was refined. Coolant temperature, and fuel rod center temperature were selected as figures of merit (FOMs) because these parameters are the most concerned in the thermal hydraulic analysis of the reactor. The LHS method was used to generate 5000 groups of parameters, their relative uncertainties were measured, and the upper and lower limits of tolerance interval and the range of tolerance interval were measured by Wilks’ method. The results show that the uncertainty of output parameters is different at different locations. In general, the tolerance range of maximum coolant temperature and maximum fuel rod center temperature is about 0.7 K and 2.2 K.