Abstract

Fuel bundles in nuclear power plants are subjected to severe operation conditions, such as highly turbulent coolant flow, high temperatures and excessive irradiation doses. These irradiation doses affect the microstructure of the material in terms of segregation and precipitation in addition to swelling. For instance, densification occurs when material pores are removed after irradiation. In contrast, swelling occurs when gaseous pores of fission products start to fill materials used in the reactor core components. All these effects influence the mechanical properties of the material and consequentially its dynamic characteristics. The present study aims at developing a fully-coupled three dimensional numerical model that utilizes the irradiated fuel bundle material as a non-linear material rather than a linear one. The non-linearity is accounted for with the aid of a constitutive model that describes the thermal and irradiation effects on the mechanical properties. Then this constitutive model is integrated in an in-house finite element code that is capable of predicting the dynamics of non-linear material. The model is applied to a CANDU fuel bundle, in which each fuel element is discretized using 12-DOF beam elements and the endplates are discretized using plate elements. The dynamic response of the fuel bundle is investigated under turbulence excitation, which is generated by the coolant flow inside the pressure tube. Moreover, the fuel-to-fuel and fuel-to-pressure tube contact is also included using the single point contact method (SPC). The dynamic response of the fuel bundle along with the associated impact forces and work rates are investigated over a range of flow velocities that are typical to those in an actual CANDU power plant. A summary of the results is presented in this paper.

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