In this study, lattice physics calculations were carried out to evaluate the reactor physics characteristics of different advanced fuel lattices cooled with 7 LiOH/NaOH or FLiBe and moderated externally by graphite and various types of metal hydroxides, such as 7 LiOH, 7 LiOD, Mg(OD) 2 , and ZrE(OD) 4 . The lithium in these compounds is enriched to 99.995 at. % 7 Li/Li. Such lattice fuel concepts could be used in compact, thermalspectrum, high-temperature (700°C) small modular reactors (SMRs). For an SMR with a bare core size of diameter = height = 163.3 cm, there are several lattice design concepts identified that could achieve modest power densities (up to 18 MW/m 3 ) that are higher than those found typically in high-temperature gas cooled reactors (~ 2 to 10 MW/m 3 ) [IAEA Technical Document 1382(2019; Report PNR-131-20110914, Delft University, Netherlands (2011)], although lower than those found typically in SMRs based on light water reactor technology (for example, the NuScale SMR has a volumetric power density of ~47 MW/m 3 ) [Proc. PBNC 2018, p. 270 (2018]. In addition, there are lattice designs identified for the fixed core size that could achieve high fuel burnup (up to 126 MWd/kg), long core lifetimes (up to 24 years before refueling), very good fissile utilization (up to 640 MWd/kg-fissile), and very good relative uranium utilization (up to 44% of that achieved with a conventional pressure-tube heavy water reactor using natural uranium fuel). The best lattice concept found to maximize fuel burnup with 7 LiOH/NaOH coolant was an 18-cm-pitch lattice with ZrE(OD) 4 external moderator (126.5 MWd/kg). The best lattice concept for FLiBe coolant was a 16-cm-pitch lattice with 7 LiOH external moderator (125.99 MWd/kg). Although it is recognized that there are numerous and challenging technical issues to be resolved, particularly with corrosion and materials science, the potential use of hydroxides as coolants and/or external moderators could lead to very important performance improvements for very small and compact SMRs.