My money's on nuclear. Advanced nuclear designs regularly claim 25 year timeframes for design, qualification testing, licensing activities, supply chain develop

My money's on nuclear. Advanced nuclear designs regularly claim 25 year timeframes for design, qualification testing, licensing activities, supply chain development, and construction. Transatomic is proposing concepts that require long qualification and licensing developments, many of which could make meaningful progress in a small lab with a $10M initial budget. You have to produce your salt fuel and do materials testing with surrogate fission products (e.g. stable isotopes) over long periods of time. They also have to do hydride transport experiments which can be done on a pretty small scale.