Sorry for the late reply, Esther!
I forgot that the Radial “transition” in Premiere isn’t a Video Transition at all, but instead a Video Effect, so you have to work it differently:
To go from Clip 1 to Clip 2, put Clip 1 on V2 and Clip 2 on V1.
Apply the Radial Transition effect to Clip 1 and set a keyframe for the “Transition Completion” parameter to 0 when you want the wipe to start. Make sure the Wipe Direction dropdown is set to Clockwise.
Go forward on the timeline and set another keyframe at 100 where you want the transition to end. You’ll see Clip 2 revealed by the wipe.
Now go to Clip 2, apply the same effect, and set two keyframes at the same times as V1, but make the first keyframe 100 and the second one 0, and set the Wipe direction to Counterclockwise.
Now, as you offset Clip 2 to the right on the timeline, as the V2 wipe reveals V1, the V1 wipe will reveal Clip 2 a bit later, and it will look like a black border on the radial wipe. The more you offset Clip 2, the larger the border.
That was a long way to go to get that effect, and I hope I haven’t confused you! Good luck!
Greg