I have worked in several correctional facilities. I do not see how this could occur to the scope the inmate says given the level of observation applied to the inmates. I have no doubt it does happen, but I believe less than indicated here. Still, such barbarism has no place in the correctional system.
Chain gang?
I agree - allowing rape has no place in prisons. I think it depends on the prison, some places rely more heavily on inmate self-policing to keep order than others, and I suspect those are the places where this sort of thing is most common. Still, it should not happen. And prisoners who engage in sexual assault of other prisoners should be publicly castrated in the prison yard....