New Design Core Options of Micro-Modular Lead Cooled Fast Reactors (MMLFR) for Facilitating Natural Circulation

초록

This study extends previous work on the reference core model of a micro-modular lead-cooled fast reactor by introducing new core designs that aim to facilitate natural circulation through the increased fuel pin diameter, higher pitch-to-diameter (P/D) ratios and reduced active core height. The reference core features a 1.6 cm pin diameter, a 1.18 P/D ratio and 130 cm active core height, while the new cores have 2.0 cm fuel pin diameter, 1.30 P/D ratio and 110 cm height. Four core options are designed to have longer cycle lengths than 38 EFPYs (Effective Full Power Years), higher burnups than 50 MWd/kg burnup, and smaller burnup reactivity swing than 1 $ at BOC. The single region core using uranium fuel offers a longer cycle length and a more negative void worth than the reference core. However, it exhibits lower discharge burnup and a more skewed power distribution. In two-region core models, the radial and axial regions of the inner fuel are optimized to increase cycle length and burnup. As the results, it was possible to significantly increase cycle length up to 51 EFPYs (70 MWd/kg) with uranium fuel only and up to 70 EFPYs (95 MWd/kg) using TRU-containing fuel in the inner region. The two region cores using only uranium fuels have negative or small positive coolant void worth but the one using TRU-containing fuel in the inner region has a slightly higher positive coolant void worth. © 2024 AMERICAN NUCLEAR SOCIETY. All rights reserved.