I've heard any fruit or nut wood is good to use besides the old standbys.
Try it and see how you like it. Experiment! We'll need a full report on the Walnut. ;D
Weber WSM, Weber GA, Weber Spirit S-320
Charbroil Oilless Turkey Fryer
Wife LuzziAnn 1956 model.
Maverick ET-732, Superfast LSU Purple Thermapen