Computations of three-dimensional deformations of hexagonal ducts compared with experimental results

A fuel pin cladding failure resulting in fission gas release will create a pressure-pulse loading on the internal walls of a subassembly hexcan duct. This pressure pulse will attenuate as it travels towards the ends of the hexcan with the result that a three-dimensional, transient pressure loading is exerted. A three-dimensional, finite-element structural code SADCAT (Structural Analysis for 3-Dimensional Core Assembly Transient) has been developed to compute the hexcan response to such loadings. The dynamic response of an EBR-II hexcan to a fuel pin failure was simulated experimentally by gas-pressurizing a centrally located tube to the bursting point. The hexcan test rig was immersed in water. The gas escaping from the tube rupture created a pressurized bubble in the surrounding liquid, and under the action of the internal loading the walls of the hexcan deformed. The resulting pressure, strain, and deflection data were recorded. The gas discharge from the rupture is described in an analytical model, the corresponding bubble formation and pressure-pulse distribution within the hexcan subassambly are computed with an implicit hydrodynamics code called ICECO (Implicit Continuous Eulerian Code). The resulting computed pressure distribution provides the input to the SADCAT computation for the dynamic response of the hexcan. An FFTF out-of-pile hexcan was slowly pressurized to failure and the deformation response as a function of pressurization was measured. These deflection data were compared with the three-dimensional code computations. Within the elastic range, computations by a two-dimensional code STRAW, with suitably modified elastic moduli to account for the stiffening effect of the end constraints, compared well with the full three-dimensional SADCAT computations