Testing shadow shields.

[Skript88]

Blocking radiation is something that typically done with very dense and heavy materials. So when you using a nuclear thermal rocket, while it would be safest to encapsulate the engine or even construct the engine out of dense radiation blocking materials It isn't practical as it adds a ridiculous amount of mass.

The low mass option is to place a disk (or bowl) of said material between said radiation source (NTR) and the rest of your ship. This disk would cast a cone shaped shadow of safety.

Img source : http://www.projectrho.com/public_html/rocket/radiation.php "From NUCLEAR SPACE PROPULSION by Holmes F. Crouch."

This is not something modeled in KSP or even in most KSP mods that add NTR's, and so what, after all it wouldn't be very fun to throw a ship together with a Nerv engine only to throttle up and find you gave your kerbals suden death syndrome. 

However because of this cone shaped safe region It could give NTR propelled spacecraft a signature look with propellant tanks or radiators tapering off toward the engines. examples:

Both images grabbed from same link as above. Left is artwork by TauCeti Deichmann shows propellant tanks a little better. Right is part of atomic rockets realistic fusion designs. http://www.projectrho.com/public_html/rocket/realdesignsfusion.php#asteroidcrewtransport <= some cool stuff here too.

Interested In how I could accurately make a realistically shaped nuclear rocket myself in blender I followed the steps here : http://www.projectrho.com/public_html/rocket/advdesign.php under Radiation Backscatter. However rather than given in steps its more of a narrative of how one guy figured out how to do it so I decided to make a little tutorial. (vid is very brief like 4:30)

I've come to like this more pointy look to nuclear rockets and if anyone else is interested in hard scienceifying their models this should come in handy.

[Vanamonde]

Skript88, I'm not seeing your pictures. Are you copying a link from an image hosting site? 

[Nibb31]

There was a Russian concept for a military version of Soyuz (Soyuz VI) that used RTGs instead of solar panels. The RTGs dangled off the side in their own reentry capsules and could be recovered after the mission. Interestingly, they were oriented to use shadow shielding to protect the crew from radiation: