prison design has taken leaps and bounds in the last 20 years. designs which allow for continuous observability, and few "blind spots" have slowed such issues down considerably, along with the use of cameras. the design you speak of is a "podular" design, which is what I worked in as a Corrections deputy. The block is shaped like a "Q" with the control bubble sticking into the center, which controls the cell doors and block access doors. common areas are in the middle of the circle and there are no blind spots, and are never far away fron the officers gaze. Physical plant design is very important in corrections management now.
CC
Strangely enough a similar round prison design called the "panopticon" was proposed in 1791 by the philosopher Jeremy Bentham.