A new simulated transient test capability is introduced that allows controlled biaxial strain-rate (CBSR) tests on fast reactor cladding to be performed at constant test temperatures ranging from 425 to 650°C and constant diametral strain rates between 10−5 and 10−3/s. The CBSR test results from both irradiated and unirradiated 20% cold-worked Type 316 stainless steel are reported. A mathematical expression describing CBSR strengths was developed from tensile data. The CBSR ductility was generally found to be reduced from corresponding tensile results by roughly an order of magnitude. For unirradiated cladding, diametral failure strain was relatively strain-rate independent below 650°C, and at 650°C, failure strains increased with decreasing strain rate. Following fast reactor irradiation at 370 to 680°C cladding, diametral failure strains increased with increasing irradiation temperature. The sensitive diameter measurement apparatus allowed strain determinations showing the importance of anelastic effects at low plastic strains.