FEM-based estimation of reactivity change due to core deformation in SFR

In sodium-cooled fast reactors, the fuel assembly deformation due to thermo-mechanical effects, irradiation, and structural restrictions results in very tangled behaviors. Reactivity feedback caused by this deformation or distortion of the assembly is a key parameter in the inherent safety analysis of fast reactor systems. However, to date, there has been no accurate and efficient deterministic way to compute directly the reactivity change caused by actual local perturbations. To overcome this difficulty, the multi-group diffusion equations are solved by the Galerkin finite element method (FEM) with linear shape functions to directly estimate the reactivity change due to local core deformations in sodium-cooed fast reactors. Assessment of reactivity changes were conducted for 5 types of deformation scenarios, and it is shown that diffusion analysis based on FEM with linear shape functions can properly estimate the reactivity change by geometric perturbation in fast reactors with less than ∼2.5 pcm error. (authors)