Pease Please PLEASE! Take your Uro off of the crushed walnuts.
When I got my first Uro, almost 10 years ago, I also housed him on crushed walnuts because that is what the pet store told me to do. I had never had a reptile before, let alone a Uro and did not know any better. Once I found out what crushed walnuts could do to the inside of a Uro though, I switched him off of them immediately. Admittedly I did not have a problem with them (at least not knowingly), but when I think about the horrible things that COULD have happened I cringe.
The three (possibly 4)mainly accepted substrates are (in no particular order) 1) sterile washed playsand, 2)birdseed, 3)dirt/sand/other mixture 4) (sometimes) papertowels, tile, etc.
There are pros and cons to each, and if you search the forum you will find many discussions outlining them. If you have any questions let us know. 
Elizabeth
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1.0 Mali Uro Archimedes (May he rest in peace)
0.0.1 Egyptian Uro Zuberi Mosca Khu (Mosca)
0.0 Fish
0.1 Sulcata Minnie
1.1 Iguanas Flik and Loki
0.1 Newfoundland Jasmine (RIP)
0.1 Feline Winter
Indiana & Wisconsin