Applying the Serpent-DYN3D code sequence for the decay heat analysis of metallic fuel sodium fast reactor

Highlights: • Micro-depletion model was implemented in DYN3D. • The model enables to obtain time-dependent spatial decay heat distribution. • A 3D SFR core model was used to verify the method and compare against Serpent. • The difference in decay heat is 0.5% between DYN3D and the reference Serpent solutions. - Abstract: Recent developments of the reactor dynamics code DYN3D have introduced the micro-depletion model which allows for explicit calculation of radioactive decay heat. Such a unique combination of nodal diffusion, thermal hydraulic (T/H) and depletion solvers allows DYN3D to perform fuel cycle depletion and obtain detailed core isotopic concentration and decay heat distributions. More importantly, this capability allows for the generation of time-dependent spatial decay heat distribution, which is essential to predict the behavior of the reactor under off-nominal scenarios. The new sequence utilizes considerably less computational resources than coupled Monte Carlo-T/H-depletion systems, but with comparable accuracy. This capability was recently tested on a limited number of simple unit cell models. The main objective of this work is to further verify the decay heat calculation capabilities of DYN3D by applying it to a considerably more realistic and detailed full core model. For the purpose of the current analysis a 3D full core model of Advanced Burner Reactor (ABR) was adopted from the OECD/NEA Benchmark for Neutronic Analysis of Sodium-Cooled Fast Reactor Cores with Various Fuel Types and Core Sizes. In this work, the Monte Carlo code Serpent was used to generate macro- and microscopic parameters, and the neutron diffusion code, DYN3D, was used to perform neutronic and depletion analyses. Detailed spatial isotopic and decay heat distributions obtained with DYN3D were verified against the equivalent Serpent reference 3D full core solution. Results indicate very good agreement between the Serpent-DYN3D code sequence and the reference Serpent solutions, with a discrepancy in total decay heat on the order of 0.5%.