A coordinate transformation method to simulate non-uniform radial deformation of nuclear reactor cores

• Modelling non-uniform mesh deformations with nodal diffusion. • Test cases ranging from simplified geometries to a real experiment with flowering. • Demonstration of dynamic simulation for pressure wave-induced core deformations. • Straightforward implementation into existing solvers. This paper presents the development of a neutronics modeling methodology for handling non-uniform mesh deformations in a deterministic 3D reactor core dynamics simulator. Coordinate transformation is applied to solve physical problems in deformed geometries, while using a numerical solver originally derived for regular geometries. Specifically, this paper introduces and evaluates a method based on coordinate transformation to simulate non-uniform deformations of nuclear reactor cores and their impact on the reactor physics behavior. The method, developed for the 3D reactor core simulator DYN3D, is applicable to any nodal diffusion-based reactor physics solver. It was tested in four stages using sodium-cooled fast reactors: (1) proof of concept on a simplified core; (2) feasibility of modelling flowering scenarios in a realistic core; (3) performance evaluation through the Phénix reactor core flowering experiment; and (4) applicability to dynamic deformation scenarios, such as pressure wave propagation.