I don’t think it’s possible to detect the radioactive contents of an orbiting satellite from 300 miles away.
Current space radar can SEE through the Earth's surface down 30 miles to detect if not resolve tectonic plates sinking ~ Geology magazine abot 2 and a half years back had a great article on the use of space radar to look at the plate plunging underneath/near the magma plume that underlies Yellowstone.
It's all in the sensitivity of the receptors and the capability of the computer software to figure out what it is.
So, yup, you can find a shipload of ceramic floor tile from China with the requisite uranium content FROM SPACE.
Those were the usual $6 per square foot tiles ~ and they went on sale ~ once they were allowed to land ~ since that radioactivity wasn't of serious concern ~ for about $0.60 per tile. I did the basement!