What is nuclear fission?

I think this article has a typo. It says "Nuclear power now provides an estimated 85 percent of the electricity we use." But, I do not know of a single country where that is true, today. A few do have over 50%, for instance Belgium at 51% and France at 60%. Ukraine had 55% before the Russian invasion. But, for the world, this source https://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-power-in-the-world-today.aspx says "Nuclear energy now provides about 10% of the world's electricity from about 440 power reactors."

After years of public activists and politicians fighting the concept of using nuclear power, the fraction of electricity produced with it has been decreasing steadily. But, the combined priorities to reduce CO2 emissions while providing reliable supplies of electric power have made people and politicians rethink the issue. And the energy supply disruptions caused by the Russian invasion of Ukraine and the resulting sanctions has governments that have been phasing out nuclear power making U-turns to keep some old reactors going or even restarting some that have recently been shut down. For example, the Palisades nuclear power plant in Michigan is now 50 years old, and was "permanently" shut down this spring, but is being supported for restart by the Michigan government. See https://www.mlive.com/news/kalamazoo/2022/09/plan-emerges-to-reopen-palisades-nuclear-power-plant-but-federal-grant-key.html .

So, basically, the world lost several decades of being able to use nuclear power to reduce greenhouse gas emissions from the 1980s to the present, as projects were cancelled. Much of that lapse was due to public fear that that was caused by the accidents at Three Mile Island, Chernobyl, and Fukushima and the tone of the media coverage of those events. Whether the public can be convinced to accept nuclear power again, now, will depend largely on how well the safety record of the current crop of power reactors holds up until they are decommissioned.

The U.S. regulatory agency for nuclear power (first the Atomic Energy Commission, and then the Nuclear Regulatory Commission) has been publicly proclaiming for many decades that the probability of a nuclear reactor having an accident that melts its radioactive core in on the order of one-in-a-million per reactor per year of operation, based on numerical risk modeling. However, the actual statistical probability is closer to one-in-a-thousand per reactor per year, to date. And the probability that those events will cause major releases to the public areas is calculated at one-in-ten but has been more like one-out-of-two.

New plant designs are configured to make melt accidents less likely and releases less serious if a melt occurs. For instance, one new design has the reactor naturally circulate its cooling water so that it is not dependent on electric power to keep its cooling capability, and it's containment building is completely submerged in a large pool of water so that the water would "scrub" much of the radioactivity out of any gases releases.

But, with the Zaporizhzhia nuclear power plant in Ukraine currently being threatened by the Russian army capture and ongoing battles in that area, we are probably very close to having yet another nuclear incident that could sour the public against use of nuclear power to make electricity without making CO2.