Small reactors are still being designed and built. the trouble with large light water reactors is that utilities won't build new ones these days. It's not just the permitting issue but also the potential liability to the power company post Three Mile Island; Chernobyl; and Fukishima. No locality wants them around any longer even though new reactor designs are far safer than the older ones. Toshiba just took a $6B write-down on its US nuclear power business (they bought Westinghouse some years ago).
The safety of nuclear power plants is dependent upon the competence of the people involved in the design, construction and maintenance of such plants. When economic issues are involved, the competence of those involved can be compromised. People to tend to take risks in the interests of an economic gain.
For example, the Fukushima disaster is obviously a very tragic event caused by an unpredictable but natural geological event; a tsunami resulting from an earthquake, a once-in-a-hundred-years event in terms of severity, or perhaps even the worst tsunami in a thousand years in that location.
But the facts remain, that the east coast of Japan has been subject to many tsunamis during the past millenium. There are even stone monuments on that east coast, with inscriptions advising future generations not to build their homes below the level of the monument.
The people who made the decision the build the Fukushima reactor close to sea level, surely must have been aware of the historical record of those past tsunami events, but because there was no such event in living memory, they took the risk, presumably assuming that it might be another hundred or 2 hundred years before another tsunami hit.
Those who are alarmed about tiny increases in a clear and odourless gas called CO2, which is essential for all life, would naturally be alarmed at the prospect of future nuclear catastrophes, so the option of efficient nuclear plants as an alternative energy source is not on the table.
Climate change alarmists might be a bit dumb, but they are not
that dumb.