Yes, it's never been profitable. The first photovoltaic device was built in the 1830's, and mass photovoltaic deployment only became profitable in the last decade. R&D in fission is absolutely not complete. The investment in it has been pathetic since before computer modeling existed, there's no way there aren't efficiencies to find. So much of the field references papers from the 50s and 60s, because that was the last time there was money and a non-strangling amount of regulation. Thorium reactors, theoretically much safer and cheaper, have barely even been tried.
It would take a huge capital investment to get a program like this off the ground, so it's too risky for the market. The invisible hand's rejection is not the same as impossibility.
> The first photovoltaic device was built in the 1830's, and mass photovoltaic deployment only became profitable in the last decade.
This is a bizarre comparison. The US invested about $1.5T total in developing nuclear power. Almost nothing was invested in developing PV. If only 1% of the money wasted on developing nuclear power had instead been invested in PV, nuclear power would have been dead by 1970. A recently passed bill earmarks $6B to keep nuclear plants open. Compare to recent DoE announcement to spend $82M on PV manufacturing. Even with this nearly two orders of magnitude imbalance of spending, PV is going to beat the pants off nuclear by making tons of money compared to nuclear power losing mind-boggling amounts of it.
R&D can not make nuclear energy cheaper. It is simply commercially unviable. If you can figure out a way to make it profitable, you can have all the nuclear energy you want, but a lot of smart and capable people spanning 4 generations have already tried and failed.
It would take a huge capital investment to get a program like this off the ground, so it's too risky for the market. The invisible hand's rejection is not the same as impossibility.