How to crack a Walnut
Short stubby screwdriver
Insert into the crack and twist
Bingo, 2 half shells, each with half a nut (which may need further prying to pop out of the half shell)
As for sorting, The good ones are denser. You can do something with floating in water or tossing through air. A cross-wind would sort the bad ones downwind.
Build a pneumatic nut-chucker and automate the process.
