The biggest risk I've seen is that unanticipated events (including financial events) will completely shutter a unit, like San Onofre and Indian Point 2.
If your average cost overrun is around 100%, then it absolutely is financially risky. And selling years in advance is not just possible but necessary for nuclear plants - people would never agree on such prices 10-20 years from now so the have to be locked in even as the plant is being built.
Some real costs are hardly predictable: hot waste long-term management, decommission (see the UK case) and especially any boo-boo (Fukushima cleanup costs will be in the ~500bn USD range) do threaten the financial model.
By all means go to current financial markets and ask for huge loans in this low-interest-rate high-inflation market. It isn't even about risk (though risks caused by regulation/government oversight are manifold). It's about return, or the lack thereof.
