Development and application of a multi-physics and multi-scale coupling program for lead-cooled fast reactor

In this study, a multi-physics and multi-scale coupling program, Fluent/KMC-sub/NDK, was developed based on the user-defined functions (UDF) of Fluent, in which the KMC-sub-code is a sub-channel thermal–hydraulic code and the NDK code is a neutron diffusion code. The coupling program framework adopts the "master–slave" mode, in which Fluent is the master program while NDK and KMC-sub are coupled internally and compiled into the dynamic link library (DLL) as slave codes. The domain decomposition method was adopted, in which the reactor core was simulated by NDK and KMC-sub, while the rest of the primary loop was simulated using Fluent. A simulation of the reactor shutdown process of M 2 LFR-1000 was carried out using the coupling program, and the code-to-code verification was performed with ATHLET, demonstrating a good agreement, with absolute deviation was smaller than 0.2%. The results show an obvious thermal stratification phenomenon during the shutdown process, which occurs 10 s after shutdown, and the change in thermal stratification phenomena is also captured by the coupling program. At the same time, the change in the neutron flux density distribution of the reactor was also obtained.