A core physics design and analysis of micro-modular lead cooled fast reactor (MMLFR) cores for autonomous ultra-long-life operation

Minimizing core size with keeping an ultra-long-life operation cycle is very interesting for improving the inherent safety and sustainability of nuclear energy systems. Additionally, minimizing the excess reactivity change to less than 1$ for the small core is very helpful to make the small nuclear reactor to be safer by removing the prompt critical accident and to make it easy for autonomous operation by minimizing the movements of the control rods. In this work, Micro-Modular Lead-cooled Fast Reactor (MMLFR) cores of 35 MWth are neutronically designed by using the superb neutronic properties of the lead coolant and considering simple two-region cores of different fuel compositions. The results of the analysis showed that the final candidate cores have cycle lengths longer than 30 EFPYs (Effective Full Power Years) over which the burnup reactivity swings are less than 1$, achieve high burnups exceeding 58 MWd/kgHM, and possess all negative reactivity coefficients except for reactivity coefficients by coolant expansion. Also, it was shown that the final candidate cores can maintain the integrity of fuel rods from point of view of DPA, peak cladding and fuel centerline temperatures, and internal pressure and hoop stress for the fission gas plenum over the operation life.