If you completely scrap and strip down a microwave and remove the magnetron from the microwave then the microwave will not be radioactive or set off any radioactive alarms at scrap yards.
I've taken microwaves to the scrap yard before and they said it had to have the magnetron removed otherwise it would be radioactive.
Once the magnetron was removed and thrown away in the trash then the microwave was accepted by the scrap yard and no longer radioactive.