I think there are other ways of getting large payloads off Earth other than Orion, and I don't think we have to resort to it under normal circumstances. For one thing, who needs the political grief.

However, as a low-tech, quickie solution to launch something real important, say, a large mass driver designed to divert an asteroid in a limited time window, it might be the first choice.

As for fallout, when I was a kid they told me not to eat the snow because of the Strontium 90. I did anyway, and somehow it didn't kill me. I did avoid the yellow stuff though.

For the record, low doses of radiation (0 - .1 Sv or about 10 rems--about 200 chest X-rays worth if my numbers are right) have not been found to significantly increase cancer risk in test populations (Hiroshima, Chernobyl).