Powder metallurgy development at SRL

The Savannah River Laboratory (SRL) is developing a powder metallurgy (P/M) process for manufacturing reactor-grade fuel tubes containing high wt % U3O8-Al cores clad with 8001 aluminum. The P/M cores are made by isostatic compaction. They are assembled in billets, outgassed, and hot-extruded using conventional coextrusion techniques. Cores have been compacted with up to 100% U3O8 and tubes extruded with 80 wt % oxide cores. Irradiation tests have been made using P/M core tubes in the Savannah River reactors. These tubes contained U3O8 concentrations up to 59 wt % and no significant swelling or blistering occurred. The tubes were irradiated to ∼ 40% burnup or 1.6x1021 fissions/cc of core. This report discusses both small-scale and production tests for high-density P/M fuel development. The purpose of the P/M development program at SRL is to: determine the maximum U3O8 content that can be fabricated into thin wall tubes, irradiate high-density tubes to high burnup and assess irradiation and dimensional stability, continue metal forming studies for extrusion and drawing, and evaluate hydrostatic extrusion and hydrostatically assisted drawing of P/M core tubes. Experimental results of testing the fuel assemblies performance so far indicate that: cores containing fine (-325 mesh) U3O8 and aluminum powders can be made practically free of high-density areas using the outlined P/M pre blending and sieving techniques. U3O8-Al cores can be isostatically compacted with up to 100 wt U3O8 and tubes successfully extruded with up to 80 wt oxide; fission gas blistering of U3O8-Al P/M tubes as indicated by the blister tests is a function of fissions/cc of U3O8 in the core; Decreasing the fission density of oxide increases the threshold temperature for blister formation; U3O8-Al P/M fuel tubes with up to 59 wt U3O8 have been successfully irradiated in SRP reactor to 1.6 x 1021 fissions/cc of core or 7 x 1020 fissions/cc of U3O8 small-scale metal forming tests sufficiently mock up production operations so that variables can be initially tested in the laboratory; parametric metal forming studies show a relationship between measurable variables of tooling temperature, half die angle and core composition. Lower temperatures and larger die angles 50-60 deg C favor extrusion of high density fuel tubes