DISSOLUTION OF BeO-AND Al$sub 2$O$sub 3$-BASE REACTOR FUEL ELEMENTS. PART I

Aqueous methods for recovering uranium from BeO- and Al/sub 2/O/sub 3/- base gas-cooled-reactor fuel elements are being evaluated. Two methods for processing Hastelloy-X--clad pelletized BeO-base fuels containing 60 to 70% UO/ sub 2/, such as the GCRE and MGCR, seem feasible. One method involves mechanical stripping or chopping of the cladding followed by leaching of the uranium from the fuel pellets with boiling 6-l3M HNO/sub 3/. In the other method the cladding and UO/sub 2/ are dissolved in boiling 2M HNO/sub 3/-4M HCl. In either case, most of the BeO matrix remains as an undissolved residue. Pellets containing 70% UO/sub 3/ dissolved completely in less than 20 hr in boiling 8M HNO/sub 3/ containing either 2M H/sub 2/SO/sub 4/ or 0.5M HF, producing solutions containing 4 g of uranium per liter. Fuels of high BeO content, e.g. BeO--5% UO/sub 2/, dissolved only slowly in boiling aqueous reagents. Highest initial rates were in sulfuric acid solutions, log (Rate, mg min/sup -1/cm/sup -2/) = 0.223 (H/sub 2/SO/ sub 4, M) - 2.8l and in HF--NH/sub 4/F solutions. ln boiling 5-8M NH/sub 4/F the initial dissolution rate increased from 0.07 to 3.5 mg min/sup -1/cm/sup -2/ as the HF concentration increased from 0 to 20M. Leaching, with boiling l0M HNO/sub 3/, of uranium from UO/sub 2/--Al/sub 2/O/sub 3/ fuel pellets was studied briefly. In 4 hr leaching uranium recoveries from pellets containing l0- mu grains of UO/ sub 2/ dispersed in an Al/sub 2/O/sub 3/ matrix decreased from 99.99 to 11.6% when the Al/sub 2/O/sub 3/content of the pellets increased from 3.7 to 61.1%. The uranium concentration was l.0M in the case of complete dissolution. (auth