I wish I could draw you a picture. But the reality is, if you can imagine your kettle at home, inside you have a heating element. For the purpose of clarity, let's say that the heating element represents the steel tubes that are inside a boiler. What they effectively do is take the steam tubes and assume them to be contaminated. The rest of the kettle in my example would be determined to be scrap metal. It would have to pass a test that it is in fact scrap metal, in which case there is no radioactive element to it, and it would be free released.
