It offers passive operation and decay heat removal and redundant control to make it walk-away safe. During nominal operation and after shutdown, the VSLLIM reactor is cooled by natural circulation of in-vessel liquid sodium (Na), that is enabled using in-vessel chimney (1–2?m tall) and helically coiled tubes Na-Na heat exchanger, placed at the top of the downcomer. The reactor can generate 1.0–10?MWth, depending on the height of the chimney and the HEX design, at an average fission power density up to 23.47?MWth/m3. The VSLLIM reactor can potentially operate continuously, without refueling for ∼92 and 5.9 full power years (FPY), respectively, and slightly below atmospheric pressure, owing to the sodium low vapor pressure. The core is loaded with hexagonal assemblies of fuel rods with UN enriched to 13.76%, and has independent systems for emergency shutdown and nominal control.