Simulation test on interactions of zircaloy claddings deforming in fuel assembly under LOCA conditions

In a hypothetical LOCA of LWR, it is assumed that Zircaloy claddings of fuel assemblies occur ballooning and cause thermal and mechanical interactions among themselves. To investigate the phenomena, burst tests were conducted with a single rod fuel simulator placed in the center of eight non-pressurized external heater pipes. It was found that the deformation and rupture behavior of ballooning cladding which made contact with the pipes depends on the following conditions: (1) temperature difference between cladding and heater pipes; higher temperature in the cladding than in the pipes produces an extended deformation and contact area, (2) internal pressure of cladding, and (3) temperature level at which ballooning takes place. It was observed and analyzed that cladding hoop tensile stress is largest at the inflection points generated in the contact surface of the expanding cladding. (author)