Nuclear history is much stranger than “big concrete power station.” Some reactors went under ice, onto military trailers, onto barges and into orbit. Here are the most interesting examples — with the place, year, scale and source attached.
These are not all the same kind of “power” record: some are individual reactors, one is a whole multi-unit site. The logarithmic scale is deliberately used so the extremes can fit on one line.
70 MWe total · Pevek, Chukotka, Russia · Commercial since May 2020
The first and only U.S. fission reactor flown in space. It produced about 500 watts of electricity and operated for 43 days before a spacecraft fault shut it down.
Experimental Breeder Reactor-I became the first power plant to produce usable electricity from atomic fission. On the first day it lit four 200-watt bulbs; the next day it powered its building.
The Army wanted a compact plant that could travel by standard military trailer, rail, ship or aircraft. ML-1 proved that a reactor package could be made truly transportable, although the programme never became an operational fleet.
Radiant moved its Kaleidos reactor hardware more than 1,000 miles on a trailer to Idaho for installation in the DOME test bed. It was transport for testing — not a reactor operating while driving down the highway.
Built for a remote Arctic base beneath the ice, PM-2A showed that a reactor could be shipped in modules, assembled far from conventional infrastructure, operated for several years and then removed.
The MH-1A reactor was installed in a converted World War II Liberty ship and supplied electricity while moored in Gatun Lake. The U.S. Army Corps of Engineers describes Sturgis as the first floating nuclear power plant.
Two KLT-40S reactors provide electricity and heat from a moored floating power unit. World Nuclear Association identifies it as the only floating nuclear power plant currently in operation.
The EPR unit entered regular electricity production in 2023. Operator TVO describes OL3 as the most powerful nuclear power unit in Europe.
TEPCO lists seven units with a combined plant capacity of 8.212 million kW. It is one of the world’s largest nuclear power stations by total site capacity; unit-by-unit operating status must be checked separately.
Single-unit output, gross electrical output, net output to the grid and total capacity of a multi-reactor site are different measurements. That is why this page labels Kashiwazaki-Kariwa as an 8,212 MW site total, while Olkiluoto 3 is a roughly 1,600 MWe single unit.
There is another current wrinkle: EDF reported that Flamanville 3 reached 1,669 MW of gross electrical power in December 2025 during its start-up programme. Gross and net figures are not interchangeable, and commissioning status matters, so we avoid turning one number into a misleading “world champion” headline.
The point is not just trivia. Seeing a 500-watt space reactor, a 300–500 kW mobile prototype, a 70 MW floating plant, a 1,600 MW unit and an 8,212 MW multi-unit site on one page makes the enormous range of nuclear applications intuitive in a way a definition of “SMR” cannot.
Freshness: current-status claims on this page were checked on 21 September 2026. Historical dates are linked to NASA, DOE, U.S. Army Corps of Engineers, INL/NRIC, TVO, TEPCO and World Nuclear Association sources directly on each record.