Kidney biopsies & dialysis catheters are the bulk of procedures in nephrology. As Stormreaver mentioned, U/S and Fluoro guided training for tunneled catheters is becoming more common as well.
Some programs are offering training in "interventional nephrology" where training for renal angiograms and RA angioplasty and stenting is being done. I don't know where or how prevalent these programs are.