I'm not a chem major but I am trained in radiological controls.

Part of the problem with radioactivity spills from bombs or reactor breaches is that there are a wide range of radioactive fission products released. Some of which decay on their own in a short time because they have short half-lives, some of which are so long-lived that they essentially "never" go away. Some short-lived elements decay to longer-lived radioactive elements too. It's a big messy mix.

This means that a chemistry based approach isn't likely to be complete.
For example, if you treat for iodine to remove it, what about Strontium? What about Co90? Will the chemistry to precipitate Iodine work on Strontium or Cobalt?(or the other dozen possible materials)?

I'm sure a chemist could concoct something to remove all the radioactive elements if you told him beforehand what they are or will be. But without this knowlege, a chemistry-based approach seems to me to be unlikely to work.

BTW- I DO have a couple of radiacs. One is a chargeable (very short term use) personal dosimeter exactly like what I used in the Navy when entering a known radioactive area (such as the shutdown reactor compartment). The other is a Civil Defense area radioactivity detector. It self-tests ok but without a radioactive test source to try it on I don't know if it works. What we had aboard ship were several additional calibrated, expensive, instruments. We also had several specially trained people who had a lot more training in the art.
Doing this at home on your own is not terribly practical.

So I personally try my best to not be present when accidents or detonations happen :-)