Hard to see how open source nuclear reactors would work. Open source works well for software because getting to the 80% solution is fun, and most people only need the 80% solution. An 80% nuclear reactor isn’t useful to anyone, and even getting to 80 percent is not that fun. Getting to 20% is a blast, but then it is time to do all of the tedious work.
Edit: I should have your Rickover link before posting. It captures my point in more detail, and with more pith.
How? China or India uses the opensource work and takes the design further. Then we license it from them like we do with existing designs.
It's not like you clone the plans off a Github repo and build an uncertified nuclear reactor in your basement, order nuclear fuel from Amazon and power up your house. Instead it'a bit like what happened to Android: it started as an OSS product but then Google added their services on top which make it actually useful.
Edit: I should have your Rickover link before posting. It captures my point in more detail, and with more pith.