Awesome simulation tool, but why is nuclear power absent from the simulation?

It's not! The strangely named "Dispatchable 2" can be turned on as an option; it's based on the economics of the EPR (although you can change all the assumptions as needed.) If you do that, you'll find the solutions tend to be either "no nuclear" or "all nuclear", depending on the cost assumptions. This is a counter to the people who suggest "renewables, but use nuclear to cover the last 20%", which is a dumb idea.