Pin-by-pin and Subchannel Simulation of a Sodium-cooled Fast Reactor minicore with FENNECS and FENNECS/ATHLET

Abstract

The geometric flexibility of the GRS neutron kinetics code FENNECS and the coupled code FENNECS/ATHLET opens up high-fidelity simulations of sodium-cooled fast reactors (SFR) at pin and subchannel level for the assessment of local safety parameters. To this aim, a minicore model consisting of seven fuel subassemblies of the China Experimental Fast Reactor (CEFR) was considered. Several pin-resolved simulations with FENNECS using the diffusion and the SP₃ solvers were compared with respective Serpent Monte Carlo reference calculations. Three different radial boundary conditions were applied to gradually decrease neutron leakage: all-sides vacuum, axially reflective and radial vacuum, and all-sides reflective boundary conditions. To perform the evaluation, the effective multiplication factors were compared with the Serpent reference results and the root mean squared errors of the normalized pin power distributions were calculated. Overall, FENNECS simulations show a good agreement with the results obtained by Serpent. The FENNECS SP₃ results are closer to the reference Serpent results than the diffusion simulations. 3 Additionally, coupled pin-by-pin steady-state and transient simulations were performed using FENNECS coupled with the GRS thermal hydraulic system code ATHLET. The results demonstrate the basic applicability of FENNECS to SFR multi-physics simulations including transients for which in future the coupling FENNECS with the subchannel code CTF will be used.