I know there were some test engines, but none every flew to my knowledge. The problem is they spit out radioactive matter over everything they fly over and expose the occupants to a lot of radiation (since you can only contain the radiation so much when you have weight limits to make). They are badass though.

When you demand power from the reactors they make a lot more radiation. There wasn't a way to shield the crew without a lot of lead plating.

Lots of weight in an aircraft was the deal breaker. I think the ruskies did end up with something flying but I'm not confident about that.