How green/seasoned is it? If it's freshcut or recently cut you'll need to season it carefuly and slowly to have any chance at all of it drying without splitting. If it's seasoned you'll need to use it clad to something else for strength, sort of a backing to glue it to for support and strength. Somebodyt else will probably be along with more specific advice about Walnut in particular, I don't know if it might be suitable for a stool seat or some such.
I've never been fortunate enough to get hold of a piece of any size.
What are it's age, dimensions etc.?