From what I understand, in the case of the radon-contaminated nuclear worker, what they actually detected were the "radon daughters", the decay products of radon. Radon itself doesn't stick around very long, but when it decays it produces an atomic dust of polonium, lead, etc. That dust is what tripped the alarms.
Anything like that radioactive source from Australia would set of tons of alarms in a nuclear power plant. You wouldn't get it out the door. Incidents like that missing radioactive source in Australia happen where there are far fewer safeguards than at a nuclear power plant. Those sources generally go missing from abandoned medical equipment, food irradiation facilities, and that sort of thing. You'd be hard pressed to smuggle (let alone accidentally convey) something like a spent nuclear fuel pellet out of a power plant.
Anything like that radioactive source from Australia would set of tons of alarms in a nuclear power plant. You wouldn't get it out the door. Incidents like that missing radioactive source in Australia happen where there are far fewer safeguards than at a nuclear power plant. Those sources generally go missing from abandoned medical equipment, food irradiation facilities, and that sort of thing. You'd be hard pressed to smuggle (let alone accidentally convey) something like a spent nuclear fuel pellet out of a power plant.