The result would be [drum roll] not very much.
At present the material remaining in the reactor building ruins has been decaying for 33 years. In another 50 years it will have been decaying fully 80 years.
This is trinity crater, the site of the first atom bomb. I've been there. It was exploded in 1945, so is now just over 80 years old. The radiation is round about double normal background, as measured by a guy wandering around with a Geiger counter. A guy in shorts and sandals. No special radiation protection is required. It's a tourist site with kids and old people wandering around.
The only real protection needed is to prevent people taking chunks of Trinitite as souvenirs. I bent down, picked up a chunk, looked around at the guy in army gear and carrying a machine gun. And he was looking at me. So I carefully put the chunk back, and he relaxed.
By the time of the beginning of your scenario, the material from Chernobyl will be marginally more radioactive than the Uranium that was mined to produce the fuel. By the end date of your scenario it will be round about the same. If you dumped roughly 100 tonnes of Uranium out of a rocket the result would be much more worrisome from the standpoint of heavy things falling from the sky than it would from radiation.
The real question is, why would anybody bother shooting this stuff into space? The energy costs would be huge, and the benefit is minimal.
Edit for comments.
Only a small fraction of the Uranium in a nuclear weapon fissions, typically a few percent.
The fission products from a weapon are similar to that in a reactor. There are minor differences in the concentration of different isotopes. The Uranium that does not fission goes through very similar reactions as in a reactor.
The danger of an isotope depends on the half life and the amount, but also the kind of radiation it emits, and how well absorbed it is by living things.
If the half life is very short then the isotope is dangerous but decays quickly, so after several half lives it becomes much less dangerous.
If the half life is very long then it produces very little radioactivity per hour.
Neptunium has isotopes with half lives of 396 days or less, or over $1.54\times 10^5$ years. So at 80 years pretty much all the dangerous stuff is gone.
Plutonium is primarily an alpha emitter. Unless you eat it, it's not really a problem. Similarly, Uranium is primarily an alpha emitter.
The dangerous items are the fission products with intermediate half lives, that are gamma emitters, and that are also absorbed by living things. The big ones are usually Strontium and Cesium. Scroll down this article to Health Concerns.
From the same article comes this graph. 10 thousand days, has already passed, and the total gamma dose is already less than 1% of what it was shortly after the accident. The decay continues, and in another 50 years will be much smaller than that, probably about .01 percent of the first day dose.
