Three Mile Island (1968), a power plant in Londonderry, Pennsylvania, illustrates the risks inherent in early reactor design: a partial meltdown of its No. 2 pressurized water reactor (PWR) core was followed by rising cancer rates in the surrounding area, and the reactor was decommissioned in 1979. Reactor No. 1 continued operating for four more decades, until its own decommissioning in 2019, a decision now under review after Donald Trump's administration, inaugurated in January 2025, revived plans to bring it back online.
Pathfinder, the second plant to draw lasting attention, represented a different kind of risk: not operational failure, but technological overreach. Built in Sioux Falls, South Dakota, in 1958, it saw Allis-Chalmers attempt to convert a standard pressurized water reactor into a superheated steam reactor, a far more ambitious design intended to sharply raise the plant's power output.
Until then, coal- or gas-fired equipment had been used to superheat steam, a process that leaves it free of droplets visible to the naked eye. Allis-Chalmers took a different approach, moving the superheater directly into the reactor itself, a design choice intended to save space and to put the residual heat from fission to further use, feeding it back into the steam that drove the generator.
The trade-off proved unstable in practice. Contemporary assessments from September 1967 suggested that the plant had operated at full capacity for only about 30 minutes, generating 58 megawatts of electricity in that window. This widely held claim, however, understated the reactor's intended capabilities: Pathfinder had in fact been designed to reach a far higher output, of up to 203 megawatts.
Pathfinder was decommissioned in 1968, with no plans for its restoration. Yet these two incidents mark the extent of the US nuclear industry's setbacks: no comparable failures followed. Europe and East Asia were not so fortunate, and the disasters recorded there would go on to shape the entire industry far more profoundly.
On 26 April 1986, the No. 4 graphite-moderated reactor (RBMK-1000) at the V. I. Lenin power plant near Chernobyl overheated, triggering a massive explosion that dispersed radioactive material across northern Ukraine and southern Belarus. The fallout reached beyond the former USSR, contaminating parts of Eastern Europe and Scandinavia as well.
Chernobyl's legacy proved to be as much cultural as political, resurfacing in the popular imagination through a five-part miniseries in 2019. Fukushima's, by contrast, translated directly into policy: the 2011 disaster led not only Tokyo to shut down nearly all of its nuclear facilities.
On 11 March 2011, the Fukushima Daiichi Nuclear Power Plant was struck by the six-minute Tohoku undersea earthquake and the tsunami that followed, a disaster of a kind Japan had long known to expect. Despite widespread awareness that the country lies on the Pacific Ring of Fire and is cyclically threatened by earthquakes and tsunamis, its most consequential nuclear facility was not built to comply with safety protocols designed for exactly this scenario.
While boiling water reactors (BWRs) 1 through 3 suffered core meltdowns and were shut down as early as 2011, the other three followed two years later, and Japan went on to decommission as many as 16 reactors at various power plants in the years that followed. That retreat has since given way to a partial reversal: last year, Sanae Takaichi's government revised Tokyo's strategy, moving to restart the remaining operational reactors. Of the 33 that were operational, 15 have been restarted so far.
By 31 December 2021, Germany had also shut down three of its last six nuclear power plants, namely Brokdorf, Grohnde and Gundremmingen, and in April 2023 it shut down Isar, Neckarwestheim and Emsland as well. Yet even this final step proved less final than intended: the decommissioning of Brokdorf in January 2026 turned out to be a 50-year project.
Peter Altmaier, then head of Chancellor Angela Merkel's office, admitted in an interview with the daily Neue Zürcher Zeitung that he was concerned about the consequences of a blanket phase-out of nuclear power. The criticism soon moved from private doubt to public rebuke: about two weeks after the plants were shut down, then opposition leader Friedrich Merz described the move as a "serious strategic mistake".
That critique proved politically consequential. He came to power on the strength of this message in May 2023, and one of the decisive steps that followed was Berlin's declaration that it would not block the inclusion of nuclear power among green energy sources at the European level.
Central Europe's Nuclear Ambitions
Despite having no nuclear power plants at all, Poland plans to build as many as nine BWR facilities, with the first ones scheduled to go online as early as 2030. Rather than following the large-reactor path taken by established nuclear states, these will almost exclusively be small modular reactors, a technology gaining traction across the EU precisely because it allows newcomers to skip decades of institutional experience. The BWRX-100 reactors are being built by Japan's Hitachi in collaboration with the Polish energy company Orlen.
Some of the planned reactors are to be built by the American company Westinghouse, which in October 2024 expressed its willingness to participate in the construction of a new unit at the Jaslovske Bohunice nuclear power plant in Slovakia. That interest was formalized when Bratislava and Washington signed an intergovernmental agreement on the development of the Slovak nuclear sector at the beginning of the year, launching the implementation phase in mid-February.
Diversifying the sources of Slovakia's nuclear technology is one of Prime Minister Robert Fico's key arguments in favor of the plan. Existing reactors already run on fuel from Russia, and fuel rods will now also need to be imported from the US.
In May, the Slovak nuclear regulatory authority approved the launch of the fourth unit at the Mochovce power plant. The same period saw Fico pay two visits to the Élysée Palace in March, after which the Slovak Nuclear Energy Research Institute and its French counterpart, Framatome, entered into a cooperation agreement.
That agreement, together with parallel deals between the French company and firms from the Czech Republic, Slovakia, Hungary and Finland, will allow these countries to develop VVER-440 reactors on their own, without Rosatom's involvement, giving Emmanuel Macron's government an entry point into Central Europe's civilian nuclear sector and a means of displacing Moscow as a strategic partner.
Slovakia is already a top performer in civil nuclear energy: nuclear power plants account for more than 60% of its energy mix, placing the country second globally, behind France (67.3%). Once the Mochovce plant is completed, however, studies suggest that nuclear power's share of the energy mix would rise to nearly 78% of covered consumption.
At that ratio, this small Central European country would hold the highest share of nuclear energy in the world, a position France is unlikely to concede for long. On 30 June, Slovenske elektrarne began transporting fuel to the fourth unit at Mochovce.
The Cleanest Energy Is Not Renewable
No other form of electricity generation matches nuclear energy for efficiency. The capacity factor, which measures a plant's normal output against its maximum potential output in megawatts, is higher for nuclear reactors than for any other power source.
The US Department of Energy's website notes that nuclear plants achieve a capacity factor of roughly 92%, well ahead of gas-fired plants at 56.6%. Wind (35.4%) and solar (24.9%) round out the bottom of the list.
A nuclear reactor with a maximum output of one gigawatt, for example, will typically deliver 0.92 gigawatts to the grid on an average day. A single solar panel supplies just 320 watts, a gap that explains why solar power depends on sprawling fields of panels to produce meaningful amounts of electricity.
This staggering efficiency is what keeps countries with a developed nuclear sector investing in new technologies for the long term. Small modular reactors are growing in popularity across the EU, but the agenda extends further still, to fusion reactors that fuse hydrogen nuclei rather than split uranium, from the Texatron system to the international ITER project in southern France.
Yet nuclear energy cannot be classified as renewable, for one simple reason: spent nuclear fuel cannot yet be recycled. The renewable category is reserved for resources considered inexhaustible, among them water, wind and the sun.
Even the European Commission's website draws a clear line between the nuclear and renewable sectors, a distinction that likely explains why it took the Commission so long to classify nuclear power as a green technology, though pressure from Germany and Austria undoubtedly played its part as well.
Renewable technology rests on one defining feature: it draws on a closed system, the Earth itself. A wind power plant does not consume wind the way a coal-fired plant consumes coal, and solar technologies, whether photovoltaic panels or photothermal mirrors, do not, in principle, deplete the sun, any more than hydroelectric or tidal plants deplete water.
Nuclear reactors work differently. Uranium, plutonium and thorium reactors rely on fission, a process that destroys the atoms of these elements: when struck by a neutron, the uranium-235 isotope splits into isotopes of barium and krypton, which can undergo further fission in turn. A nuclear reactor thus consumes fuel, only far more slowly than a coal- or gas-fired power plant does.
Nuclear power avoids the conventional emissions of thermal plants, but it leaves a different legacy: spent nuclear fuel. In Slovakia, this is handled by the state-owned company JAVYS, the Nuclear and Decommissioning Company, which typically stores it in sealed containers buried underground.
That is not the only option available, however. Nearly 97% of this waste still consists of uranium that can be dissolved in acid, reprocessed and converted back into fuel rods, an approach that remains costlier than mining fresh uranium.
Texatron, mentioned earlier, offers a different route, using high-temperature plasma made up of deuterium nuclei – an isotope of hydrogen with one neutron – and helium-3. As these high-energy particles move in a cyclic pattern, they undergo fusion, a process expected to yield up to 500 megawatts of power in the reactor.
Some nuclear waste, meanwhile, can be turned into nuclear batteries, something the Chinese company Betavolt managed as early as January 2024. The technology hinges on 63 different isotopes, whose radiation converts into photons that then dislodge electrons from the atoms of a conductor.
That process mirrors how solar panels work: radiation hits a metal surface, releasing electrons and producing a current. In the United States, this approach, known as photon-based direct energy conversion (PIDEC), is being developed largely under the Pentagon's research arm, the Defense Advanced Research Projects Agency (DARPA), which has already contracted several companies through its Rads to Watts program.
Nuclear power plants still run on the same basic principle as fossil-fuel plants: a heat pump, in which steam pressure from a heat source, be it coal, natural gas or uranium, drives a turbine. It is a fairly rudimentary setup, yet the prototypes outlined here suggest a genuine break from the nuclear-powered steam engine.
