Somebody expressed displeasure at the idea of just crashing nuclear engines on your home planet, so I made a modification to the Mark Twain by putting radial separators and parachutes on the nuclear engine side pods. A test showed that the small parachute was not sufficient, so I put on the large chute used by the 3-kerbal capsule:
Then I did a fractional orbit mission to drop a Twain into the big desert area on Kerbin. After descending to 35 km, I cut loose the landers, the nuke sidepods, and the capsule. Around 20 km the chutes popped out on the pods just as planned.
Here the capsule and the four nuke side pods are descending gently.
The landings looked great...but then the side pods fell over, and the full fuel tanks on top of them exploded. But the nuclear engines survived just fine. Later tests showed that a water landing is gentler and does not explode the fuel tanks even if they land full.
So, for the extra expense of carrying some additional weight around the planetary system, I can be more environmentally friendly to Kerbin.