There are two possible junkyard assignments, simply 'Junkyard', or otherwise 'Junkyard with no visitors'.
Sims skilling up in the Inventing skill can collect scrap for their inventions, either by digging through junk piles or by detonating objects. Sims can also salvage regularly spawning burnt and broken objects. SimBots can also eat scrap at the junkyard.
Juan's Pick 'n Pull
Juan's Pick 'n Pull is one of the two default junkyards for Twinbrook. The name of the lot suggests that it is owned by Juan Darer, but he does not own the lot officially. It may refer to the fact that Lacy Darer has her grave stone on the lot. She died in a fire, presumably the fire that destroyed Juan's home.
Bayless Memorial Junkyard
Pick 'n Pull Junkyard
Pick 'n Pull Junkyard is the default junkyard in Appaloosa Plains if Pets is installed.
Grady's Junkstop is automatically placed in the player's lot bin when Ambitions is installed. It will be the default junkyard that will be placed in most neighborhoods, except Twinbrook and Appaloosa Plains.
Obtainable scrap Piles
If you put a Kleptomaniac Sim in a scrap yard there is a chance they will steal one of the scrap piles. You can then find it in your family inventory and place it on your home lot.