That's only true at low penetration of renewables. When you approach 100% clean energy, even current new nuclear actually looks just as cheap or cheaper as the combination of curtailment (i.e. over-building nameplate capacity and throwing away much of the energy), storage, and transmission you need to produce reliable power with wind and solar alone.
(and for the same reason, we should be looking at expanding hydro and geothermal)
So while I definitely think we should build solar and wind, it's ridiculous to just dismiss nuclear out of hand for cost reasons if the goal is 100% clean energy (unless you have, say, massive amounts of hydro power).
Given the climate emergency, it's silly to pit one clean energy project against another when in fact we need all we can get. Particularly in the case of variable renewables, as they benefit tremendously from being in a source-diverse power grid.
They are still in the process of building it, and it is set to become the second most expensive building built in modern times. [0]
[0] https://metropolitan.fi/entry/olkiluoto-ol3-second-most-expe...