An Expanding Plug Test Method for Determining Hoop Stress-Strain Curves of Irradiated Nuclear Fuel Cladding

A method, referred to as the expanding plug test method, for determining the roomtemperature hoop stress-strain curves of irradiated nuclear fuel cladding has been developed and applied to evaluate tensile strength and ductility in the hoop direction of clad material irradiated to high neutron fluences. The test utilizes an incompressible plug fitted within a tubular cladding specimen. A cylindrical punch is used to compress the plug axially, which generates a radial displacement that acts upon the inner diameter of the specimen. Position sensors track the radial displacement of the specimen outer diameter as the compression proceeds. An auxiliary compression test of the plug alone is also performed. Using these two sets of data, a procedure was developed to determine the hoop stress in the clad specimen. The development of this simple, cost-effective, highly reproducible test method to determine stressstrain curves in the hoop direction of irradiated clad specimens represents a significant advancement in the mechanical characterization of irradiated cladding. This paper will present an overview of the expanding plug testing technique and will discuss tests performed on irradiated clad specimens to date.