Maybe worry less about the power plant and more about where the spent fuel pools are located because when the power is down for "a long time" those 40' deep pools are going to warm up real quick and there will be a spectacular explosion. Without power that water is going to not be cooled and will warm, and warm, and heat up, and then *BOOM*
www.ips-dc.org/files/3200/spent_nuclear_fuel_pools_in_the_US.pdf
www.ips-dc.org/files/3200/spent_nuclear_fuel_pools_in_the_US.pdf