That's a weird metric (one meltdown is quite a catastrophe) and the calculation seems suspicious too. Between Chernobile and Fukushima I don't see how this could be correct.
I do find your other points more convincing, though with some "citation needed" wrt. coal.
And that's before we consider the environmental and health risks of ash ponds[2], which can (and have caused) heavy metal pollution in nearby groundwater supply. The largest industrial spill in US history happened barely a decade ago, and was an ash pond[3].
Edit: I can personally recommend "The Buffalo Creek Disaster" (ISBN 9780394723433) as a writeup by a lawyer involved in a similar coal ash accident (one that directly killed over 100 people).
[1]: https://www.pnas.org/doi/10.1073/pnas.2017936118
[2]: https://en.wikipedia.org/wiki/Ash_pond
[3]: https://en.wikipedia.org/wiki/Kingston_Fossil_Plant_coal_fly...
In Finland's case, the realistic alternatives are burning coal or burning Russian gas. (If the Finns dedicated a substantial chunk of their forests to this one generator, they could maybe use biomass.)
Coal kills two orders of magnitude more people per GWh than nuclear--and it does that when operating nominally, not when malfunctioning--and it produces three or four orders of magnitude more waste and more environmental harm from mining.
Russian gas has geopolitical/national security problems.
Biomass is a roundabout way of burning diesel fuel and gas, while degrading and eroding forest soils and polluting watersheds.
The number of new meltdowns per decade rounds to zero, to five significant figures.