"Slow down progress?" That's just terribly obvious framing.
Actually by voting this way they're speeding up progress towards modern renewables. After all, nuclear fission technology is not a "modern" technology, it's over a half century old and it's simply not needed anymore (Bonneville Power Administration shut down its nuclear plant for refueling and their coal plant was shut down because it was unnecessary and still had excess power to export -- 100% from renewables so please, please don't post stupidly about "baseline" power.)
They're in a particularly sunny climate, there are already rolling out solar thermal storage systems so that their solar can generate 24 hours per day, They have tidal sources which France used to generate hundreds of megawatts back in the 60's out of a single installation -- ignoring the efficiency increases of what we can do today.
Fuel is finite, so fuel based sources are out of date. Meanwhile, renewables just keep coming down in price. Solar dropped 20% last year alone, and is expected to drop another 20% this year. Meanwhile, nuclear keeps increasing in cost. Costs for implementation, fuel, owner's costs, massive grid tie-ins, and let's not even discuss the fact that they don't pay for their own insurance and push that on to the public purse in the event of a catastrophe.
So "progress?" I don't think that word means what you think it does. The first world has made it's decision and you can flog the dead horse of nuclear, but the only new adopters will be the third world and powers that want to refine for nuclear weapons, such as arabic countries, Pakistan and Bangladesh.