A walk-away safe, Very-Small, Long-LIfe, Modular (VSLLIM) reactor for portable and stationary power

Abstract

This paper describes a Very-Small, Long-LIfe, and Modular (VSLLIM) reactor design, developed at the University of New Mexico’s Institute for Space and Nuclear Power Studies, which offers passive operation and decay heat removal and redundant control. 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. It also has two independent systems for safe passive removal of decay heat after shutdown, and following an unlikely malfunction of in-vessel HEX. These are liquid metal heat pipes (LMHPs) embedded in the primary vessel wall, and natural circulation of ambient air along the outer surface of the guard vessel wall. The LMHPs are thermally coupled to thermoelectric elements for generating 10 s of kW of auxiliary DC power, independent of on-site and off-site sources, both during nominal reactor operation and after shutdown. The sodium coolant enters the fast-neutron energy spectrum core at 610 K and exits at ≤755 K, depending on the reactor thermal power. At these temperatures, Na is compatible with the HT-9 Ferritic-Martensitic steel cladding, core structure and reactor vessel. The reactor would be fabricated, assembled and sealed at the factory, and transported by rail, truck or barge to a permanent site and installed underground, to protect against an airplane or a missile impact, and mounted on seismic isolation bearings, to resist earthquakes. At the site, the VSLLIM module could use a superheated steam Rankine cycle or a supercritical CO2 Brayton cycle for electricity generation at high thermal efficiency. Alternatively, a VSLLIM power module, with an open air Brayton cycle, could be deployed on a portable platform or a truck, to provide both electricity and/or process heat at remote sites, hospitals, data centers, natural disaster areas, arid or desert regions, and advanced military bases.