Control and shutdown rods for pebble-bed reactor - having arrowhead tips to loosen bed spheres during withdrawal

摘要

Device comprises generally cylindrical rods of absorber material with tapering points, which are lowered vertically into the pebble-bed core. The lower part of each rod is so shaped that, when it is withdrawn, some of the spherical elements of the bed are raised, thus causing the bed to be loosened. Pref. lateral projections at =1 points near the tip of the rod considerably increase its cross-section. This general arrowhead shape is interrupted by vertical slits to permit free passage of vertical guide elements for the rods. In a variant, other parts of the rod may comprise indentations at =1 points, in which spherical elements tend to become lifted as the rod is withdrawn. Device is used for a pebble-bed reactor, which repeated movement of the control and shut-down rods would otherwise result in compaction of the bed. The use of a head of this type enables the bed to be repeatedly loosened in a simple manner, thus preventing irreversible compaction.