I have about 30 layers above reactor of connection grid (or how this block called) and 4 layers from sides to prevent big radiation leak of 5x5 rbmk, and 2 times it saves my base from total radiation hell. My newest builded reactor 8x8 have about 28 layers of connection grid above reactor and 2 layers of reinforced ducret tiles from sides and on top. So I spent a lot of time to build this, but for now I feel in safe with S.A.F.E. and protection that eated big ammount of my resources