Yes somewhat harmful to the environment but not as harmful to the environment as a nuclear war.
I feel we as a species need to get better at weighing up the costs of our action or inaction, making hard choices rather than everyone just fighting blindly for one half of the equation. /rant
Unfortunately, we've set up all our systems - governance, markets - to work through fighting. Politics, business and negotiations all work the same way: every side fights for their immediate short-term interest. One team wins this battle, other team wins that battle, and it goes on and on, until the cost of fighting outweighs any marginal improvement any side could get - and a "compromise" is reached.
I think it all comes down to the fact that we don't trust each other at scale. Because I can't trust that you'll approach searching for solutions honestly, that you'll optimize globally, I have to fight for my own interest at expense of rationality. For the same reason, you end up fighting for yours.
It's ridiculously wasteful, and I think most of humanity's problems stem from it. I can't think of a way out of it, at scale.
The general rule of thumb is that the radiation in the fallout from a bomb goes down by a factor of 10 for every factor of 7 the time since the detonation increases. So it's 10 times less radioactive after a week as it was after a day. 100 times after a month and a half, 1000 times less after a year, etc.
Under the linear-no-threshold dose model we'd expect several death from fallout induced cancer per test. But on the other hand we know that the linear-no-threshold model is false. If you give some fruit flies a 50 REM dose of xrays all at once they get cancer. If you give them 50 REMs spread out over the course of a month they don't. But we don't really know what the actual model is very well so that's not a risk I'd be happy to take.
Bombs can be "tuned" to burn nearly all or very little of their fissable material. Radiation from the blast dissipiates nearly immediately, but the bomb would need to be designed to provide little fallout(it's doable is what I'm trying to say).
Amount of fallout depends on more things, not just settings of the bomb. Mainly on where the bomb detonates. If close to ground/water, then it's bad, lots of fallout. If in stratosphere, very little fallout.
If you burn less, you lower the yield. Burning more means you turn more mildly-radioactive plutonium or U235 into intensely radioactive fission products. Strontium-90, for example, accumulates in bones and has a half-life of 28 years.
I feel we as a species need to get better at weighing up the costs of our action or inaction, making hard choices rather than everyone just fighting blindly for one half of the equation. /rant