Burst Strength of EBR-II Irradiated Fuel Pin Sections

Abstract

Burst tests were conducted at 900°F on specimens prepared from 75% UO₂ −25% PuO₂ fuel pins clad with 0.250-in. o.d. × 0.016-in. wall Type-304 stainless steel (PNL 1-3 and 1-6) that were irradiated in EBR-II to ∼8500 MWd/MTM at 8 to 9 kW/ft. Argon gas was used internally to pressurize the fuel pin sections. The fuel was left intact in order that the effects of the fuel and fission products on the properties of the cladding could be determined. Specimens taken from above the midplane but within the fuel column exhibited brittle, intergranular fracture at drastically lower stresses (∼30 000 psi) than would be expected from Type-304 stainless steel irradiated under similar conditions. The measurable strain in these specimens was 23C₆ and sigma phase at the grain boundaries of the cladding whereas the cladding of specimens from below the fuel midplane was free of grain boundary precipitates. From the test results and examinations it is concluded that: