The U.S. Nuclear Regulatory Commission (NRC) has adopted safety goals that provide high-level guidance with regard to severe accidents. The U.S. nuclear industry is developing evolutionary advanced light water reactor designs that incorporate changes to improve operability, reliability, and safety. The NRC Advisory Committee on Reactor Safeguards has recommended a number of safety improvements for future light water reactors, many of which are receiving attention. Against this backdrop, questions are posed concerning problems in gaining assurance of the relative safety and economics of radically new reactor concepts employing new technologies.