As someone else already said - there wasn't really any risk of that, the reactor wasn't "shedding" enough radioactive material or even emitting enough radioactivity to be a danger to anyone standing on the ground. Maybe if you made it fly in a loop around one place it would start to add up, but it wouldn't be anywhere on the scale of "making the entire soviet union a nuclear death zone" - you'd need thousands and thousands of these flying across their entire landmass 24/7 for weeks if not months, which

1) is just a stupid idea

2) if you have the capability to do this, you also have the capability to detonate actual nukes which can be tuned to produce maximum amount of fallout if that's your goal.