US electric utilities operate roughly 98 gigawatts of nuclear generating capacity, and almost none of it has been added in the past several decades, according to Energy Information Administration analysis of small modular reactor and microreactor designs under development. High capital costs and long licensing timelines have kept the fleet close to flat.

The size gap between existing units and the new designs is substantial. Large scale nuclear units typically produce between 550 and 1,500 megawatts each. SMR designs target about 300 megawatts per unit or less. Microreactors, a subset of the SMR category, generally come in at 20 megawatts or less and can run on the grid, off the grid, or inside a microgrid.

EIA reviewed specifications for commercial SMR and microreactor designs under development in the United States as of February 2026 and grouped them by coolant technology. Light water cooled designs, which use water as a moderator and mostly follow pressurized water reactor practice, are typically scaled down versions of existing large designs. High temperature gas reactors use graphite as a moderator and helium as a coolant. Molten salt designs use salts as fuel, coolant, or both. Sodium cooled designs substitute liquid metal for water.

Several designs run on high assay low enriched uranium, enriched between 5% and just under 20% uranium-235, compared with the sub 5% low enriched uranium used in most reactors today. Higher enrichment delivers higher burnup, which can shrink reactor footprints and reduce spent fuel volume. EIA noted that SMRs are under consideration for powering data centers and industrial sites that may not connect to the grid.

Source: U.S. Energy Information Administration - https://www.eia.gov/todayinenergy/detail.php?id=67584