You don't want to "dry" them!
Walnuts in the shell are good for 6-months upto 1-year as long as they shell has not dried out and split - stored in a ventilated container in a cool, dry, dark place.
Walnuts are very high in unsaturated fats - so they go rancid quicker than most other nuts. For long term storage - shell them and put the nut meats in an air-tight plastic freezer bag, something like ziplock freezer bags, squeeze out all the air you can and store them in your freezer for 6-months to a year. If you have a vacuum sealer, something like a FoodSaver, they will last even longer.
To "freshen" then up before using - you can roast them in a 150-F oven for 5-10 minutes.