I have no idea whether fission plants are competitive with gas plants, and knowing a bit about multi-decade projects, I suspect no-one does. It’s all guesswork.
What I do know is fission has a horrible cost profile. First there’s a huge build cost, which can often skyrocket unpredictably. Then you’ve got a hugely profitable part where you’re basically printing money. Then there’s an enormous cost at the end.
Huge cleanup costs, whether it’s nuclear or coal, basically means either government has its eye on the ball to an excellent extent (Australia seems to be good here.) or it’s not going to be fixed except by the same government that didn’t tie down the guys who made the money enough.
I’d call fission a bad choice for countries with weak or chaotic government. You need a rock solid civil service to allow it.
(You’ll observe the same is true of almost every mineral extraction project.)