It's pretty interesting to see the effects of this type of reactor when it goes critical.If i remember right i think one of the problems in the past was what happens if something goes wrong during launch time. if the rocket crashes instead of making it all the way into space there could be nuclear waste just about anywhere on the planet depending on where it crashes. I just hope this never happens. Maybe launch it into space in a conventional way, then kick start it (fire it up, start the reaction) once it is actually in deep space.
https://www1.grc.nasa.gov/historic-facilities/rockets-systems-area/7911-2/
IV. THE REACTOR ERUPTION
https://fas.org/sgp/othergov/doe/lanl/docs1/la-3449.pdf