The problem is that the pusher plate is so heavy that you really want to launch that off planet under its own power to make it worthwhile and that would generat

The problem is that the pusher plate is so heavy that you really want to launch that off planet under its own power to make it worthwhile and that would generate some fallout. There are things you can do to minimize that but it would still be as bad as an open air thermonuclear bomb test like Castle Bravo. The nuclear powers conducted lots of those but they do kill an expected 100 people each given some assumptions about the danger of low radiation doses. On the other hand nuclear-thermal, nuclear-electric, and solar-electric are all fine ways of getting to Mars faster.