Analysis Of The Effect Of PWR Bowing Fuel Assembly On The Thermal-hydraulic Characteristics

The fuel assembly is an important component of the core,and its thermal-hydraulic characteristics are closely related to the operation safety of the reactor.The operation experience of PWR shows that with the increase of operation time,the fuel assembly will produce different degrees of bowing phenomenon,which will affect the flow and heat transfer of coolant.However,there are relatively few studies on curved fuel assemblies and the influence of mixing vane is not considered.Therefore,in order to study the thermal-hydraulic characteristics of bowing fuel assemblies and their coolants,different 5x5 fuel assembly models were established.The variation trend of coolant thermalhydraulic parameters under different bowing fuel assemblies was obtained by CFD method.Firstly,a standard 5×5 fuel assembly model was established,and the optimal mesh size was obtained by mesh sensitivity analysis.The four turbulence models of SST,standard k-ε model,RNG and RSM were compared with PIV experimental results to prove the feasibility and accuracy of the CFD method.The SST model was selected for subsequent calculation considering the calculation accuracy and speed.Then,5x5 fuel assembly models with two bowing dimensions of 1mm and 2mm under three bowing shapes of C-shape,S-shape and W-shape were established respectively.The CFD calculation of the fuel assembly under six bowing conditions was carried out.The analysis results were compared with the standard straight rod for multiple parameters,including the average cross-sectional lateral velocity,temperature and normalized Nusselt number.It was found that different bowing conditions in the downstream would lead to a decrease in heat transfer efficiency.At the same time,different sub-channels are divided,and the changes of flow velocity,pressure and temperature in different sub-channels are compared.It is found that corner channels and side channels are more affected,and the relevant parameters of the edge position of the bowing component should be paid attention to during operation.After that,the outer wall of the flow field is named,and the temperature distribution of the four outer walls is compared.The results show that different bowing shapes have different effects on the upstream and downstream.The left and right sides are more affected by bowing than the upper and lower sides.Finally,the fluid-solid coupling analysis of the fuel assembly is carried out to obtain the stress concentration and the maximum displacement position.The parameters show that the fluid load has little effect on the solid domain of the assembly under different bowing shapes and sizes.In summary,the research results of this paper have reference value for the design of fuel assemblies and the operation safety under bowing conditions.