What is the most exciting thing you ever did as a nuclear engineer?

I have done so many different things that were exciting.  Being involved in reviewing the design of nuclear submarines, getting involved in analyzing events that happened in other countries, creating nuclear based policy for the US and for the world through participation in IAEA activities, but the most fun and exciting thing I did in my career was to work with NASA on providing power for the Mars rovers, designing a lunar power station,  and also working with the Office of Naval Reactors on the design of a nuclear powered rocket for an exploration mission to the icy moons of Jupiter.  It really stretched my knowledge base and I met so many smart people!  That is what is so great about being a nuclear engineer - so many different opportunities!