[en] A number of special issues for the Flibe design are described. The salt tubes immersed in the bed of beryllium balls must be spaced so the balls can flow into or out of the tube region with no bridging resulting in flow stoppage. We have conducted flow tests which show that if the balls are no larger in diameter than one-half of the free space between tube walls, free flow will occur. Since some balls may crack or swell and develop imperfections of shape, we prefer that the ball diameter not exceed one-third of that free space. The pebble size is picked to be large enough to avoid excessive pumping power but small enough to freely flow between the tubes during pebble changeout and during periodic pebbles movement to allow for pebble swelling