Calandria Tube Buckling During a Reactor Core Collapse

Abstract

An experimental test campaign was conducted at Canadian Nuclear Laboratories (CNL) simulating a core disassembly event during a postulated severe accident scenario. In such an event, falling moderator levels would expose fuel channels located near the top of the calandria vessel. These fuel channels would heat up, soften, and collapse onto still-submerged fuel channels below, forming a suspended debris bed. The collapse of a column of fuel channels to the bottom of the calandria vessel would occur when the ultimate strength of the submerged calandria tubes and their rolled joints is exceeded. The tests performed at CNL quantified the strength of these structures under various transverse and axial loads. The results from these experiments can be used to improve core disassembly models such as those in the severe accident code MAAP-CANDU. This will lead to improved predictions of the accident progression, hydrogen generation rate, and radionuclide source terms.