I did this in metasequoia. It probably can be done in many modelling programs. Open a primative torus, increase size til it looks like a bagel, then extrude with bevel applied just extrude slightly or you get a real explosion spikes everywhere and it takes forever to render. you'll get it I did it by accident then went back to find out what I did. then just export back to bryce to color and render. have fun