An F82H steel pressurized tube creep capsule for irradiation in HFIR

Abstract

A novel capsule design has been developed for measurement of irradiation creep in pressurized tubes and is being used to irradiate reduced activation ferritic/martensitic F82H steel creep test specimens. These tests are being conducted in the flux trap of the High Flux Isotope Reactor at the Oak Ridge National Laboratory. The capsule design uses a tight-fitting corrugated aluminum foil placed in the center of a vanadium alloy holder to conduct heat from the centrally located test specimen. The foil acts as a compressible thermal interface between the pressurized tube and holder, maintaining a constant thermal resistance (and thus a constant tube temperature gradient) during irradiation, regardless of differential thermal expansion, creep, and swelling in the test specimen. Mechanical interference with creep deformation of the specimen tube is minimized by using a thin (0.05 mm) foil with sufficient room to crush. Finite element analysis of the contact pressure between the specimen and foil, combined with thermal creep in the foil, showed little interference with specimen stress conditions. Specimens were designed to experience hoop stresses of 380, 300, 150, and 0 MPa at a temperature of 300 °C while being irradiated to a dose of 3.7 dpa. Passive SiC thermometry is located within the pressurized tube and the holder material for confirmation of experiment irradiation target temperatures. This work discusses aspects of the capsule's fabrication and design, including thermal models of the capsule during irradiation.