Five years of production of a guaranteed ten percent of your power already being used while you transfer energy grid tech is pretty significant and a much simpler hurdle than reducing ten percent of your power across the grid.

Given that the average Californian household uses around 7200kWh a year a single facility providing 9% of the state's energy needs or 2.89 million homes isn't that bad...

For a 1.2 billion dollars investment, that is about 415 dollars per household to keep it running for 5 years more.

Not saying that new nuclear generators are the best way since we have better alternatives, but you can't knock the benefits that nuclear energy has given us. If we were to reduce energy use by 10% today wouldn't we want to burn that much less natural gas and that little share of coal first if we cared about health impact? This buys us more time to have renewables displace the most harmful of generation methods.

Last operating nuclear power plant.

Which means this one plant provies 9.3% of the state's power generation. It's entirely reasonable to think that cutting that power generation without having other sources to replace it with would be a "bad idea," especially considering how Enron royally fucked California by playing games with power.