Abstract US nuclear reactors have demonstrated that they can continue to operate well beyond their thirty or forty year operating licenses which, at the time they were issued, were based on criteria for large fossil fuel power plants. Accordingly, a longevity criterion for 21st century reactors is proposed here, designed to last 100 years or more. Cheap electricity from a fully amortized long-life reactor is a gift from the generations that paid for the reactor to future generations that benefit from it, and they compensate (to a degree) for the burden of geologically sequestered wastes.