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Highlights • A new method was proposed to simulate thermal deformation of subassembly in SFR. • Assembly deformation analysis code FADAC was developed and applied in the present study. • Free bowing was analyzed under different temperature conditions and displacement field of the subassembly was obtained. • Restrained bowing was analyzed in detail and maximum deflection was calculated. Abstract Due to the special geometry and compact arrangement of subassemblies in the sodium-cooled fast reactor, thermal deformation of the assemblies are easily triggered by uneven temperature distribution in the reactor core, which is negative for reactor safety. Therefore, it is necessary for researchers and engineers to conduct quantitative analysis towards thermal deformation behaviors of subassemblies, and furthermore, give reliable evaluation results on aftermath of the assembly thermal deformation. In the present study, thermal deformation analysis code FADAC, which was developed based on Euler-Bernoulli beam theory, was applied to make numerical investigation for thermal deformation behaviors of a single subassembly in sodium-cooled fast reactor. In order to preliminarily assess the capacity for thermal deformation, different temperature gradient conditions were considered and analyzed in detail for free bowing of the subassembly, furthermore, with the aid of numerical analysis for thermal axial forces and thermal bending moments, axial displacements and deflections were calculated finally. Besides, in order to predict the comprehensive results of the assembly deformation under both thermal load and mechanical load, restrained bowing were also analyzed for different temperature conditions. All of the simulation results were in good accordance with the experimental data. The present numerical research is of great significance to assembly deformation research in the sodium-cooled fast reactor, and will surely lay a solid foundation for deformation analysis towards multi-subassemblies. [ABSTRACT FROM AUTHOR]

• Equilibrium equations and compatibility equations were conducted respectively to consider coupling effects of subassemblies in SFR. • Calculation for row bowing was performed with the aid of FADAC code in the present study. • Row bowing was analyzed in detail under different geometric parameters for wrapper tube, even core baffle was taken into consideration. • Reaction forces and deflection parameters were obtained by calculation, which are meaningful for safety evaluation and core structural design. Subassemblies in sodium-cooled fast reactor are different from pressurized water reactor in both geometry and assembly arrangement. In sodium-cooled fast reactor, assembly thermal deformation and narrow clearance between adjacent assemblies would cause them contact with each other, and reaction force between neighboring pads would occur. Under that circumstance, assembly deformation would be decided by both thermal load and mechanical load, which means significant coupling effect would lead to more complicated deformation behaviors. Therefore, so as to deeply study such thermal–mechanical coupling effect in reactor core, it is meaningful to conduct theoretical analysis and numerical simulation on such behaviors, which is indispensable for reactor safety analysis and structural design. In the present study, equilibrium equations and compatibility equations were conducted respectively for acquiring deformation parameters of assemblies in the row, which were already implemented into FADAC code and can perform calculation for row bowing. Furthermore, reaction forces and assembly deflections were analyzed in detail. Besides, sensitivity analysis were performed for row bowing calculation, in which wrapper tube thickness, distance across flat for wrapper tube, pad clearance and effects of core baffle were all taken into consideration. The present theoretical research for assembly deformation in SFR is essential for reactor safety and structural design, and will lay a solid foundation for assembly deformation analysis in the whole core. [ABSTRACT FROM AUTHOR]