First reason is natural gas, or to be more precise falling natural gas prices. By the current looks of it natural gas could be connected with low costs for at least next few decades as the new technologies (such as shale gas extraction) have hugely increased the amount of natural gas that is recoverable.
The second reason is skyrocketing cost of building new nuclear reactors. Almost every new nuclear power plant costs at least 100% more than initially projected and this is something that can’t be tolerated in energy market for a very long time. It seems like nuclear power has all of the sudden lost its competitiveness with fossil fuels, and US taxpayers do not want to pay more for renewable energy, whether alone nuclear power.
The third main reason is the recent trend of falling consumer demand for electricity which has significantly decreased the need for new nuclear power plants. Falling consumer demand for electricity is not only the result of recent recession woes but also the result of significantly improved energy efficiency. Energy efficiency is thought by many energy experts as the best energy option there is, and compared to nuclear power has more than obvious advantages such as significantly lower costs, and no safety issues, waste disposal problems and length construction delays.
From the current point of view it certainly looks like nuclear power industry will likely struggle in years to come, not only in United States, but also on global level. The only safe oasis for nuclear power looks to be France, and up to some point Japan.