Neutron diffraction study of radiation damage in U{sub 3}Si at 30{degrees}C and 350{degrees}C

Abstract

Neutron diffraction has been used to follow damage evolution in U{sub 3}Si produced by neutron irradiation at 30{degrees}C and 350{degrees}C. Increasing neutron irradiation dose at 30{degrees}C results in monotonic expansion of the a-axis and contraction of the c-axis that transforms the crystal structure from tetragonal to cubic. Additional irradiation results in amorphization. Neutron irradiation at 350{degrees}C results in little change to the a-axis and expansion of the c-axis. The complete alteration in lattice dilatation during irradiation is interpreted as due to modification of surviving defect configurations at the higher temperature. The high temperature lattice dilations can be explained by defect loop formation in the a-b plane. TEM observations have shown that ion irradiation at temperatures below 280{degrees}C results in amorphization while twin boundaries dissolve and new subgrains form at higher temperatures. Confinement of lattice strain to the c-axis during irradiation at 350{degrees}C may be the mechanism that prevents the total lattice dilatation from exceeding the critical level required for amorphization. High-density uranium silicides have potential uses in the nuclear industry for use in high power or low enrichment applications. However, U{sub 3}Si exhibits a mechanical instability during reactor irradiation that results in catastrophic swelling. Such behavior would preclude use ofmore » these materials as reactor fuels.« less