Can you link that claim?
Take a look at the ThorCon site. The last paragraph on the page reads:
Cheaper than CoalModern nuclear plants are already competitive with coal, except for the cost of regulation and lawsuits. They produce no mercury or particulates, to boot...ThorCon requires less resources than a coal plant. Assuming efficient, evidence based regulation, ThorCon can produce reliable, carbon free, electricity at between 3 and 5 cents per kWh depending on scale.
Why Molton Salt Reactors will Probably Cost a lot Less
http://nucleargreen.blogspot.com/2012/04/why-molton-sakt-reactors-will-robably_18.html
95% of all reactor grade fuel energy content ever produced is resting in storage awaiting reprocessing. Chemical processing can separate the fissionable component from contaminates. A MSR is vastly more effective at total fuel burn. Breeder versions of salt reactors should be reserved for second generation MSR development.