Abstract: A fluid cooled heat exchanger molten core retention and solidification apparatus (10) is a vertically oriented array of tube assemblies located beneath a reactor vessel. Water under forced circulation flows through inlet tube (18) into an inlet plenum (20) beneath the heat exchanger (10) up through the inner vertical tube (22), down through the annular space between the outside of the inner tube (22) and the inside of the outer tube (24) into an outlet plenum (28), then through tube (30) to a heat exchanger outside containment building (16) where heat is released. The array of vertical tube assemblies provides heat transfer surface within a few centimeters of all molten material and sufficient volume between the exterior surface of outer vertical tubes (24) to accommodate all expected molten material in the event of a meltdown of the core of the nuclear reactor.

Abstract: A bi-metallic spacer grid having a Zircaloy perimeter strip consisting of oppositely facing, thin walled metal plates for closely surrounding the array of fuel rods. A rigid, stainless steel cross member extends between internal surfaces of the oppositely facing perimeter plates. In the preferred embodiment, the perimeter plates have cantilevered portions extending above and below the main body of the perimeter strip. The cross members interact with the enlarged portion by urging them outward relative to the perimeter strip as the fuel assembly heats up during operation. The outwardly projecting interface surfaces of each assembly mechanically interact with the interface surfaces of adjacent assemblies providing a mechanical restraint which limits bowing of the assembly. The effectiveness of the spacer grids in limiting bowing is therefore not dependent upon controlling the mechanisms responsible for causing bow.